Method for calibrating total station and total station

Abstract

The invention relates to a total station and a method of calibrating a total station (500). The total station includes a central unit (510) mounted on a righting instrument (520) for rotation about a first axis (130), where the righting instrument is mounted on a base (540) of the total station for rotation about a second axis (150) orthogonal to the first axis such that an aiming axis (170) of the total station is rotatable about a point of rotation. The central unit comprises a plurality of measurement channels, where the measurement channels are associated with measurement devices (512, 514, 518) having an optical axis, where at least one measurement device is a camera (512) configured to capture images. The method includes determining a collimation error relative to the aiming axis for any of the plurality of measurement channels, thereby providing a calibrated reference measurement channel. The method includes rotating the central unit about at least a first axis to a predetermined position in which the collimated calibration beam enters the central unit through an objective lens of the central unit to further propagate toward the camera. The collimated calibration beam is associated with (i) the calibrated reference measurement channel is associated with at least one measurement channel to be calibrated if the calibrated reference measurement channel is a measurement channel associated with the camera, or (ii) the calibrated reference measurement channel is associated with the calibrated reference measurement channel if the calibrated reference measurement channel is a measurement channel other than the measurement channel associated with the camera. The method further includes capturing at least one image with the camera, where the collimated calibration beam is detectable in the at least one image; and determining a relative collimation error between a measurement channel associated with the camera and at least one measurement channel to be calibrated if the calibrated reference measurement channel is a measurement channel associated with the camera based at least on a position of an image point corresponding to the collimation calibration beam in the captured at least one image, if the calibrated reference measurement channel is a measurement channel associated with the camera, or if the calibrated reference measurement channel is a measurement channel other than the measurement channel associated with the camera, a relative collimation error between the measurement channel associated with the camera and the calibrated reference measurement channel is determined.

Description

Technical Field

[0001] The present invention relates to the field of surveying and mapping equipment, and more particularly to a total station for surveying and mapping applications and a method for calibrating the total station. Background Art

[0002] Generally speaking, surveying of land, buildings, construction sites, etc. involves determining the terrestrial (e.g., two-dimensional (2D) or three-dimensional (3D)) positions of points and / or determining distances and angles between such points. In surveying applications, a surveyor may use a surveying instrument, such as a robotic total station, which integrates an electronic distance measuring unit (EDM unit) with a movable center unit (or telescope) that is configured to rotate about at least two axes (typically a trunnion or horizontal axis and an azimuth or vertical axis).

[0003] The center unit can typically be mounted on an alidade for rotation about a first axis (e.g., a trunnion), and the alidade can be mounted on a base for rotation about a second axis (e.g., an azimuth axis) that intersects (e.g., is orthogonal) to the first axis, so that the aiming axis of the total station can rotate about a rotation point (typically corresponding to the intersection between the first and second axes).

[0004] The base is used to mount the instrument on the ground, a floor, a wall, or any other object and may comprise a tripod, for example. The base defines a first axis about which the alidade can rotate relative to the base. Typically, when preparing for surveying applications, the base is mounted so that the first axis is oriented vertically (i.e., in the direction of local gravity). The alidade defines a second axis about which the center unit can rotate relative to the alidade.

[0005] The sighting axis (or optical axis) of a total station is defined as the axis of the center unit that is orthogonal to the first axis, i.e. the axis about which the center unit can rotate relative to the alidade. The sighting axis is also the axis along which measurements are to be performed using the center unit (e.g. by an EDM unit).

[0006] To perform such measurements, the total station may further include a rotary encoder to measure the rotational position of the alidade relative to the base about a first axis and the rotational position of the center unit relative to the alidade about a second axis. The orientation of the sighting axis in a coordinate system defined relative to the base can then be determined, so that measurements performed along the sighting axis can be related to this coordinate system.

[0007] The measurement can be performed by a number of devices located in the central unit. These devices include, for example, an EDM unit for measuring the distance from the total station to the target, a laser pointer for assisting in pointing to a specific target, a reticle for aiming at the target (usually through an eyepiece), and one or more cameras for capturing images of the target or the scene around the total station and / or assisting in tracking the target. Each of these devices (or measuring devices) can be associated with an optical axis and constitute a measurement channel within the central unit, in the sense that at least one direction defined by the rotary encoder can be obtained (or measured) by these devices.

[0008] Ideally, the optical axis associated with each of these devices (or measurement channels) should be aligned with the sighting axis. However, this may not always be the case due to mechanical imperfections, such as the first axis not being perfectly orthogonal to the second axis or the sighting axis not being perfectly orthogonal to the first axis, and the situation can also change over time due to environmental influences, such as varying temperatures. Therefore, it is necessary to calibrate the total station not only at the factory but also in the field to determine any alignment errors between the sighting axis and the optical axes associated with the multiple measurement devices of the multiple measurement channels.

[0009] Traditionally, surveyors have manually measured the collimation errors of these measurement channels. However, this calibration measurement is time-consuming, requires experience, and can be prone to error.

[0010] It would therefore be desirable to provide a new and / or improved method for calibrating a total station, and a new or improved total station that facilitates such calibration. Summary of the Invention

[0011] The present invention aims to provide at least some embodiments that overcome at least some of the aforementioned disadvantages. More specifically, the present invention aims to provide at least some embodiments that provide at least one simpler and less time-consuming method for calibrating a total station. To achieve this, a total station and a calibration method are provided having the features defined in the independent claims. Further advantageous embodiments of the invention are defined in the dependent claims.

[0012] An embodiment according to a first aspect of the present invention provides a method for calibrating a total station.

[0013] The total station includes a center unit (or telescope) mounted on an alidade for rotation about a first axis, the alidade being mounted on a base of the total station for rotation about a second axis orthogonal to the first axis, such that a sighting axis of the total station can rotate about a rotation point. The center unit includes a plurality of measurement channels, wherein the measurement channels are associated with measurement devices having optical axes, and at least one of the measurement devices is a camera configured to capture an image.

[0014] The method includes determining a collimation error relative to a sighting axis for any one of a plurality of measurement channels, thereby providing a calibrated reference measurement channel. The method also includes rotating a center unit about at least a first axis to a predetermined position in which a collimated calibration beam enters the center unit through an objective lens of the center unit for further propagation toward the camera. The collimated calibration beam is associated with: (i) at least one measurement channel to be calibrated, if the calibrated reference measurement channel is a measurement channel associated with the camera, or (ii) a calibrated reference measurement channel, if the calibrated reference measurement channel is a measurement channel other than the measurement channel associated with the camera.

[0015] The method further comprises capturing at least one image with a camera, wherein the collimated calibration light beam is detectable in the at least one image; and determining, based at least on positions of image points corresponding to the collimated calibration light beam in the at least one captured image, the following relative collimation errors: if the calibrated reference measurement channel is a measurement channel associated with the camera, determining the relative collimation error between the measurement channel associated with the camera and at least one measurement channel to be calibrated, or if the calibrated reference measurement channel is a measurement channel other than the measurement channel associated with the camera, determining the relative collimation error between the measurement channel associated with the camera and the calibrated reference measurement channel.

[0016] According to an embodiment of a second aspect of the present invention, a total station is provided, comprising: a center unit mounted on an alidade for rotation about a first axis; and a base on which the alidade is mounted for rotation about a second axis intersecting the first axis, such that a sighting axis of the total station can rotate about a rotation point. The center unit includes a plurality of measurement channels, wherein the measurement channels are associated with measurement devices having optical axes, and wherein at least one measurement device is a camera configured to capture an image.

[0017] The total station further comprises at least one optical element attached to the alidade or the base, and a processing unit configured to perform calibration of the total station according to the method disclosed above, i.e., by:

[0018] determining a collimation error relative to a sighting axis for any one of the plurality of measurement channels, thereby providing a calibrated reference measurement channel;

[0019] rotating the central unit at least about a first axis to a predetermined position in which a collimated calibration light beam emitted or reflected at the optical element enters the central unit through an objective lens of the central unit for further propagation toward the camera, wherein the collimated calibration light beam is associated with: (i) at least one measurement channel to be calibrated, if the calibrated reference measurement channel is a measurement channel associated with the camera, or (ii) a calibrated reference measurement channel, if the calibrated reference measurement channel is a measurement channel other than a measurement channel associated with the camera;

[0020] capturing at least one image with the camera, wherein the collimated calibration beam is detectable in the at least one image; and

[0021] Based at least on the position of an image point corresponding to the collimated calibration light beam in at least one captured image, the following relative collimation errors are determined: if the calibrated reference measurement channel is a measurement channel associated with the camera, the relative collimation error between the measurement channel associated with the camera and at least one measurement channel to be calibrated is determined, or if the calibrated reference measurement channel is a measurement channel other than the measurement channel associated with the camera, the relative collimation error between the measurement channel associated with the camera and the calibrated reference measurement channel is determined.

[0022] The calibration method (or calibration process) according to this embodiment includes determining a collimation error relative to a sighting axis for any one of a plurality of measurement channels, thereby providing a calibrated reference measurement channel. This collimation error can be referred to as an absolute collimation error, because the sighting axis, defined by the angle read by the angle encoder after rotation about the first and second axes, determines the axis along which measurements are to be taken. If the optical axis of the measurement device of a measurement channel is aligned with (or coincides with) the sighting axis, there is no collimation error. Determination of this absolute collimation error for a measurement channel allows correction of measurements performed by the measurement device associated with that measurement channel.

[0023] The calibration method according to this embodiment includes determining the relative alignment error between a calibrated reference measurement channel and another measurement channel. The absolute alignment error of the other channel can then be determined based on the determined relative alignment error. As described above, in the present invention, the term "absolute alignment error" refers to the alignment error determined relative to the sighting axis of the total station, i.e., the alignment error determined relative to the axis along which measurements are to be performed when the angular position of the center unit is selected relative to the first and second axes. Relative alignment error refers to the alignment error of a measurement channel relative to any measurement channel, but in particular relative to a calibrated reference measurement channel.

[0024] The calibrated reference measurement channel can be, for example, a measurement channel associated with a camera of a total station. Through the aforementioned process, which includes capturing an image in which a collimated calibration beam is detectable, a relative collimation error between the measurement channel associated with the camera and another measurement channel to be calibrated, which is associated with the collimated calibration beam, can be determined. The relative collimation error can be determined based on the position of an image point (e.g., a light point) corresponding to the collimated calibration beam in the captured image. For example, if the image point (or light point) of the collimated calibration beam is offset from the center of the camera's image sensor, a relative collimation error between the camera's measurement channel and the measurement channel to be calibrated is obtained.

[0025] It will be appreciated that the collimated calibration light beam may, for example, be associated with a measurement channel to be calibrated, in that the collimated calibration light beam propagates at least partially within the measurement channel to be calibrated.

[0026] In another example, the calibrated reference measurement channel can be another measurement channel other than the measurement channel associated with the camera, such as the measurement channel associated with the EDM unit. The collimated calibration beam detected in the image captured by the camera is then associated with the calibrated reference measurement channel (i.e., the measurement channel of the EDM unit in this example). If the image point (or light point) corresponding to the collimated calibration beam corresponds to, for example, the center of the image sensor of the camera, there is no relative collimation error between the measurement channel associated with the EDM unit and the measurement channel associated with the camera. In this case, the absolute collimation error of the camera is the same as the absolute collimation error determined for the measurement channel associated with the EDM unit. However, if the image point corresponding to the collimated calibration beam deviates from the center of the image sensor of the camera, there is a relative collimation error between the measurement channel of the camera and the measurement channel of the EDM unit. The absolute collimation error of the measurement channel associated with the camera can then be obtained based on the determined collimation error of the calibrated reference measurement channel and the determined relative collimation error.

[0027] It will be appreciated that, depending on the arrangement of the camera and its associated optics in the central unit of the total station, the position of the image point (or light point) of the collimated calibration beam may be compared to the position of another point other than the center of the camera's image sensor. More generally, determination of the relative collimation error may include comparing the position of the image point to the position of a reference point (in an image captured by the camera) representing the optical axis (or measurement axis) associated with the camera.

[0028] In this embodiment, determining the relative alignment error between two measurement channels involves capturing an image. Therefore, at least one of the measurement channels involved in the method according to this embodiment is a measurement channel associated with a camera of a total station. However, as described above, the measurement channel associated with the camera can be a calibrated reference measurement channel or a measurement channel to be calibrated.

[0029] If the calibrated reference measurement channel is a measurement channel associated with the camera, the measurement channel to be calibrated (i.e., the measurement channel for which the relative collimation error is to be determined) can be any of the other measurement channels. If the calibrated reference measurement channel is a measurement channel other than the measurement channel associated with the camera, the measurement channel to be calibrated (i.e., the measurement channel for which the relative collimation error is to be determined) is the measurement channel associated with the camera.

[0030] In some embodiments, the determination of the relative alignment error may be performed for the remaining plurality of measurement channels.

[0031] An advantage of this embodiment is that the absolute collimation error only needs to be determined for one of the multiple measurement channels (i.e., the collimation error between the optical axis of the measuring device and the sighting axis of the total station). Based on the (absolute) collimation error determined for the calibrated reference measurement channel and the image of the collimated calibration beam captured by the camera, the above-described process can be used to calibrate the other measurement channels.

[0032] Furthermore, the calibration process for the remaining measurement channels can be performed using a collimated calibration beam that enters the central unit when the central unit is rotated in a predetermined position. In other words, the remaining measurement channels (i.e., measurement channels other than the calibrated reference measurement channel) can be calibrated without requiring the surveyor to aim at, for example, an external object. Thus, by rotating the central unit to a predetermined position and executing the above-described process (including capturing the collimated calibration beam in an image captured by a camera and determining a relative collimation error based on the collimation error determined for the calibrated reference measurement channel) and the captured image, calibration of the remaining measurement channels can be performed automatically.

[0033] As described above, the center unit can be rotated to a predetermined position in which the collimated calibration beam enters the center unit through the objective lens of the center unit for further propagation toward the camera. As will be explained in more detail below, the calibration beam can originate from a light source located within the center unit of the total station, or from a light source outside the center unit, such as a light source located at the collimator of the total station, or even from a light source located outside the total station in some implementations. In any case, the collimated calibration beam enters (or re-enters) the center unit for further propagation toward the camera. It should be understood that the calibration beam originating from the light source located within the center unit (or the calibration beam passing through the center unit) becomes collimated when it leaves the center unit through at least the objective lens (or front lens) of the center unit.

[0034] The optical element, such as a retroreflector or the light source itself, can be arranged so that when the central unit is rotated to a predetermined position, a collimated beam reflected at the retroreflector or emitted by the light source enters the central unit. Different embodiments of such optical elements will be described in more detail below.

[0035] It should be understood that the optical axis of a measuring device for a measuring channel may also be referred to as the measuring axis of the measuring channel.

[0036] The predetermined position of the central unit corresponds to an angular rotation of the central unit relative to the first axis.The central unit may have any angular rotation relative to the second axis to determine the relative alignment error.

[0037] According to some embodiments, determining the alignment error of the reference measurement channel relative to the sighting axis of the total station includes aiming the center unit at the far-field object. In some embodiments, determining the alignment error of the reference measurement channel relative to the sighting axis of the total station includes performing a first measurement on a first face of the total station and performing a second measurement on a second face of the total station, wherein, in the second face, the center unit is rotated 180° about each of the first axis and the second axis of the total station compared to the first face. In other words, determining the absolute alignment error of the calibrated reference measurement channel can involve a face 1 / face 2 (F1 / F2) calibration, which includes the surveyor aiming at the far-field object. However, it should be understood that determining the absolute alignment error of the measurement channel can be performed by other methods.

[0038] Furthermore, the camera for capturing images may be any one of a camera configured to capture images of a scene around the total station and a camera configured to track a target by the total station.

[0039] According to one embodiment, the calibration method can be performed to obtain a relative alignment error between a measurement channel associated with a camera and a measurement channel associated with a measurement device including a light source. The measurement device can be, for example, an EDM unit, which typically includes a light source (which acts as an emitter to emit a light beam toward a target) and a photodetector (which acts as a receiver to detect the light beam reflected from the target). However, the measurement device can be any measurement device including a light source, such as a laser pointer that can emit a calibration beam.

[0040] Thus, in this embodiment, if the calibrated reference measurement channel is a measurement channel associated with a camera, the at least one measurement channel to be calibrated includes a measurement channel associated with a measuring device including a light source, or if the calibrated reference measurement channel is a measurement channel other than a measurement channel associated with a camera, the calibrated reference measurement channel includes a measurement channel associated with a measuring device including a light source. The collimated calibration light beam originates from the light source and (re)enters the center unit by retroreflection on an optical element of a base or an alidade attached to the total station.

[0041] In other words, in this embodiment, the collimated beam is generated by a light source located within the central unit. The collimated beam exits the central unit through its objective lens, becoming a collimated beam. It is then reflected back into the central unit by retroreflection from an optical element attached to, for example, an alidade or a base. The optical element can be a retroreflector, i.e., an optical element or device that reflects a collimated beam so that the path of the reflected beam is parallel to the path of the incident collimated beam.

[0042] According to another embodiment, a calibration method can be performed to obtain the relative alignment error between a measurement channel associated with a camera and a measurement channel associated with another camera in a central unit of a total station. It should be understood that a total station can include multiple cameras for different functions, such as one camera for imaging the total station's surroundings and another camera dedicated to tracking a target. These two cameras can be located at different locations within the central unit of the total station.

[0043] Therefore, in this embodiment, the camera mentioned in the above process can be referred to as a first camera configured to capture images within a first wavelength range. Furthermore, if the calibrated reference measurement channel is a measurement channel associated with the first camera, the at least one measurement channel to be calibrated includes a measurement channel associated with a second camera configured to capture images within a second wavelength range. Alternatively, if the calibrated reference measurement channel is a measurement channel other than the measurement channel associated with the first camera, the calibrated reference measurement channel includes a measurement channel associated with the second camera configured to capture images within the second wavelength range. The collimated calibration beam includes light of a first wavelength within the first wavelength range and light of a second wavelength within the second wavelength range. The method can then further include capturing at least one image of the collimated calibration beam with a second camera. Therefore, in this embodiment, the first camera captures a first image in which the collimated calibration beam is detectable, and the second camera captures a second image in which the collimated calibration beam is also detectable. Relative collimation error can then be determined by comparing the positions of image points corresponding to the collimated calibration beam in the image captured by the first camera with the positions of image points corresponding to the collimated calibration beam in the image captured by the second camera. It should be understood that to improve accuracy, each of the two cameras can capture multiple images.

[0044] In some embodiments, the first wavelength is the same as the second wavelength. In other words, the first camera and the second camera can be configured to detect light of the same wavelength, such as light from the same light source.

[0045] Furthermore, in some embodiments, the first wavelength range is the same as the second wavelength range. Thus, the two cameras may be sensitive in the same wavelength range.

[0046] In some embodiments, the collimated calibration beam may originate from a light source of one of the plurality of measurement devices and enter the central unit by retroreflection of an optical element attached to an alidade or base of the total station.

[0047] For example, a collimated calibration beam can originate from a light source (laser source) of the EDM unit (the beam becomes collimated when it leaves the central unit through the objective lens of the central unit). The collimated calibration beam can be directed to an optical element (e.g., a retroreflector) arranged at the collimator or base of the total station and reflected back to the central unit through the objective lens of the central unit to further propagate to each of the two cameras. Thus, an optical path can be provided within the central unit for each of the two cameras, as the collimated calibration beam is detectable at both the first camera and the second camera.

[0048] Therefore, it should be understood that a plurality of measurement channels can be calibrated at a predetermined position of the center unit relative to the first axis (as defined by the angular position of the center unit). In this example, assuming that the calibrated reference measurement channel is the measurement channel associated with the first camera, a relative collimation error between the measurement channel associated with the first camera and the measurement channel associated with the EDM unit can be determined by identifying the position of an image point in an image captured by the first camera (e.g., by determining that the image point is not centered in the middle of the image sensor of the camera), and another relative collimation error between the measurement channel associated with the first camera and the measurement channel associated with the second camera can be determined by comparing the positions of image points corresponding to the collimated calibration beam in the image captured by the first camera and the image captured by the second camera.

[0049] In some embodiments, the calibration beam can originate from a beam that enters the central unit through the eyepiece of the total station (or through a measurement channel associated with the reticle of the central unit of the total station, which typically corresponds to the measurement channel associated with the eyepiece), propagates toward an optical element attached to the collimator or base of the total station, and then re-enters the central unit (through the objective lens) by retroreflection from this optical element. This embodiment is identical in principle to the above-described embodiment, except that the calibration beam does not originate from a light source located within the central unit, but rather from an external light source located outside the central unit or the total station. In this embodiment, when the calibration beam enters the central unit through the eyepiece of the central unit, it will be affected by the front lens of the central unit and thus collimated by it. Therefore, the beam originating from this light source does not need to be collimated. However, as described above, the beam is collimated when the light is reflected back at the retroreflector and (re)enters the central unit.

[0050] Still referring to the process of performing a determination of relative collimation error between two cameras, in some embodiments, the first wavelength can be different from the second wavelength. For example, the first wavelength can be in the visible light wavelength range, which can generally correspond to the sensitivity of a camera configured to capture images of the surrounding environment of a total station, and the second wavelength can be in the range of 800nm-900nm, which can generally correspond to the sensitivity of a camera configured to track a target. It should be understood that the collimated calibration beam can include light having two (or more) different wavelengths.

[0051] As another alternative to providing a collimated calibration beam, a light source can be attached to the collimator or base of the total station. The light source can be positioned, and / or an optical path can be provided from the light source, so that when the center unit is rotated to a predetermined position, the light beam can enter the center unit through the objective lens of the total station. In one example, the light beam can be provided by a light source placed behind the pinhole or a device such as a negative crosshair / reticle so that the light beam emitted from the pinhole or the device is collimated. The light source may include a first light-emitting element (or first light source) configured to emit light of a first wavelength within a first wavelength range and a second light-emitting element (or second light source) configured to emit light of a second wavelength within a second wavelength range. From the perspective of the first camera and the second camera, the first light-emitting element and the second light-emitting element (or the first light source and the second light source) are arranged to emit light from the same optical position.

[0052] Furthermore, in the case where the first wavelength and the second wavelength are the same, the collimated calibration beam can be derived from a beam that enters the central unit through the eyepiece of the total station, propagates toward an optical element attached to the alidade or base of the total station, and then re-enters the central unit through retroreflection from the optical element. The beam that enters the central unit through the eyepiece does not need to be collimated because it will be collimated by the optical device located in the central unit (more specifically, the front lens of the central unit). The beam can be derived from a light source that emits two different wavelengths.

[0053] In another embodiment, the calibration method can be performed to obtain a relative alignment error between a measurement channel associated with a camera and a measurement channel associated with a graticule of a central unit of a total station. The graticule can be arranged in front of or near an eyepiece of the central unit.

[0054] Thus, in this embodiment, if the calibrated reference measurement channel is a measurement channel associated with the camera, the measurement channels to be calibrated include the measurement channel associated with the center unit's reticle, or if the calibrated reference measurement channel is a measurement channel other than the camera's measurement channel, the calibrated reference measurement channel includes the measurement channel associated with the center unit's reticle. A collimated calibration beam can originate from a beam that enters the center unit through a measurement channel associated with the center unit's reticle (typically corresponding to the eyepiece), propagates toward an optical element attached to the alidade or base of the total station, and then, through retroreflection from the optical element, reenters the center unit to propagate toward the camera. In this embodiment, the light source illuminates the reticle, thereby projecting an image of the illuminated reticle. The reticle can be a positive crosshair (so that the reticle casts a shadow) or a negative crosshair. The image captured by the camera will contain the image of the reticle. The image point corresponding to the collimated calibration beam will correspond to the center of the imaged reticle.

[0055] For the aforementioned embodiment where the light beam originates from a light source placed at the eyepiece of the central unit of the total station, the light beam does not need to be collimated before passing through the eyepiece into the central unit. However, the light beam will be collimated by the central unit and will remain collimated when it is reflected back at the retroreflector to be directed toward the camera.

[0056] In embodiments where the light beam originates from a light source disposed at the eyepiece of the central unit of the total station, the light source can be disposed in a protective bag of the total station or in a fixed location (e.g., a wall or ceiling) for production testing, such that when the instrument is rotated to a predetermined position, light from the light source can enter the central unit. In some embodiments, the light source can be external to the central unit but still be disposed on an element of the total station (e.g., on a handle of the total station disposed at the alidade).

[0057] As described above, the center unit is rotated to a predetermined position so that the collimated calibration beam enters the center unit for further propagation toward the camera. In some embodiments, multiple measurement channels can be calibrated from a single predetermined position, such as using a light source of a measurement device of the center unit, to determine the relative collimation error between a measurement channel associated with a camera and a measurement channel associated with a measurement device having a light source, as well as the relative collimation error between a measurement channel associated with the camera and a measurement channel associated with another camera (provided that the collimated calibration beam originating from the light source of the measurement device is detectable in images captured by both cameras).

[0058] In other embodiments, the center unit may need to be rotated to two or more predetermined positions in order to perform a relative calibration between the measurement channel associated with the camera and the other measurement channel. Therefore, in such embodiments, to perform a relative calibration between the measurement channel associated with another measurement device and the measurement channel associated with the camera, the method further comprises rotating the center unit about at least the first axis to another predetermined position, in which another collimated calibration beam enters the center unit through the objective lens for further propagation toward the camera. The other collimated calibration beam is associated with the measurement channel associated with the other measurement device, and the method comprises capturing at least one additional image with the camera, wherein the other collimated calibration beam is detectable in the at least one additional image. The method then comprises determining a relative collimation error between the measurement channel associated with the camera and the measurement channel associated with the other measurement device based at least on the position of an image point corresponding to the other collimated calibration beam in the at least one additional image.

[0059] The total station may, for example, include a first optical element attached to the alidade or base to provide a first collimated calibration beam when the central unit is rotated to a predetermined position, and a second optical element attached to the alidade or base to provide a second collimated calibration beam when the central unit is rotated to another predetermined position.

[0060] The at least one optical element may include: a reflector, through which light emitted from a light source of a measuring device among the plurality of measuring devices is reflected (back to the central unit) when the central unit is rotated to a first predetermined position; and / or a light source for emitting a collimated calibration light beam having a first wavelength and a second wavelength.

[0061] The control unit of the total station as described above with respect to the first aspect may be configured to perform the method as defined in any one of the embodiments described herein.

[0062] The present invention relates to all possible combinations of features described in the claims and in the preceding embodiments. Other objects and advantages of various embodiments of the present invention will be described below by way of exemplary embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] One or more embodiments will be described, by way of example only, with reference to the following drawings (which should not be considered to scale), in which:

[0064] Figure 1A 、 Figure 1B and Figure 1C The collimation error of the total station is schematically shown;

[0065] Figure 2 Schematically illustrates a plurality of measurement channels in a central unit of a total station;

[0066] Figure 3A 、 Figure 3B and Figure 4 Determining the collimation error for a measurement channel of a total station relative to a sighting axis of the total station is shown;

[0067] Figure 5A and Figure 5B Determining a relative collimation error between a measurement channel associated with a camera and another measurement channel associated with a measurement device including a light source is shown;

[0068] Figure 6 schematically illustrates an image captured by a camera for determining relative collimation error;

[0069] Figure 7 A general overview of the method of calibrating a total station is shown;

[0070] Figures 8A-8C Determining a relative collimation error between a measurement channel associated with a first camera and a measurement channel associated with a second camera using an external light source is shown;

[0071] Figure 9 Determination of a relative collimation error between a measurement channel associated with a first camera and a measurement channel associated with a second camera using a light source of a measurement device of a central unit is shown;

[0072] Figure 10 Determining a relative collimation error between a measurement channel associated with a first camera and a measurement channel associated with a graticule of a central unit of a total station is shown; and

[0073] Figure 11 Determination of relative collimation errors between multiple measurement channels of a central unit of a total station using two or more calibration beams is shown.

[0074] While the present invention is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings, as described in detail herein. However, it should be understood that the detailed description and drawings herein are not intended to limit the invention to the particular forms disclosed. Rather, the intention is to cover all modifications, equivalents, and alternative forms falling within the scope of the appended claims.

[0075] The words "include", "comprising" and similar terms used in this specification should not be interpreted as exclusive or exhaustive. In other words, they are intended to mean "including but not limited to". DETAILED DESCRIPTION

[0076] The present invention is described below by way of a number of illustrative examples. It should be understood that these examples are provided for illustration and explanation only and are not intended to limit the scope of the present invention. Rather, the scope of the present invention is defined by the appended claims. Furthermore, although the examples may be presented in the form of individual embodiments, it should be appreciated that the present invention also encompasses combinations of the embodiments described herein.

[0077] Figure 1A to Figure 1B is a schematic diagram of an exemplary total station 100, wherein Figure 1A shows the vertical axis error (or vertical index error) of the total station, and Figure 1B The horizontal axis error of the total station is shown. The total station 100 may also be called a theodolite.

[0078] The total station 100 includes a center unit 110 mounted on an alidade 120 for rotation about a first axis 130, wherein the alidade 120 is mounted on a base 140 of the total station 100 for rotation about a second axis 150 that is orthogonal to and intersects the first axis 130, so that a sighting axis 170 of the total station can rotate about a rotation point (not shown, but the first and second axes intersect within the center unit). The center unit 120 includes a plurality of measurement channels, which are referenced to Figure 2 Describe it.

[0079] The base 140 may include a tripod 145, and the alidade 120 may be rotated relative to the base 140 about a second axis 150. In most surveying scenarios, it is desirable for the second axis 150 to be oriented vertically, and the tripod and centering base 145 are used to adjust the orientation of the base 140 so that the second axis 150 is parallel to the vertical direction defined by the gravity vector at the location of the total station 100. The center unit (or telescope) 110 is mounted on the alidade 120 so that it can be rotated relative to the alidade 120 about a first axis 130. The total station shown is designed so that the first axis 130 is oriented orthogonally to the second axis 150, and so that the first axis 130 intersects the second axis 150. The total station 100 also includes an objective lens (or front optics or front lens) 125, through which light can exit or enter the center unit 110.

[0080] The central unit 110 or telescope may comprise a plurality of measurement channels as provided by a plurality of measurement devices of the central unit. Each measurement channel is associated with a measurement device having an optical axis along which measurements may be performed. For the sake of clarity, Figure 1A and Figure 1B Only one optical axis (or measuring axis) 190 is shown. At least one measuring device of the central unit is a camera configured to capture images, such as in combination with Figure 2 Further described.

[0081] For example, the measurement axis 190 can be indicated by a reticle in the telescope's field of view, and the user can direct the measurement axis 190 toward the object of interest in the telescope's field of view by rotating the center unit 110 about the second axis 130 and the alidade 120 about the second axis 150. The orientation about the first axis 130 and the second axis 150 can be determined by reading scales provided on the total station or electronic signals generated by encoders associated with the first axis 130 and the second axis 150 in the total station 100. Based on these readings, the angular position of the object of interest relative to the coordinate system associated with the base 140 can be determined. The calculation of this orientation depends on the readings of the rotational position about the first axis 130 and the second axis 150 as input. The calculation also depends on assumptions about the geometry of the total station 100. The assumptions about the geometry include the orientation of the first axis, the second axis, and the optical axis (or measurement axis) of the measurement device associated with the measurement channel relative to each other. If the configuration of the total station deviates from these assumptions, the sighting axis determined by the rotation of the center unit about the first axis 130 and the second axis 150 (and thus corresponding to the reading on the encoder or scale of the total station) may deviate from the optical axis (or measurement axis) associated with the measurement channel. This in turn leads to inaccurate calculation of the orientation of the optical axis (or measurement axis) associated with the measurement channel in the coordinate system. The sighting axis can also be called the reference axis because it is the axis along which measurements are performed.

[0082] Figure 1A One type of alignment error is shown, which is called vertical index error (or vertical alignment error). The vertical index error represents the angle 180 between the sighting axis 170 of the total station and the measuring axis (or optical axis of the measuring device) 190. Assuming that the encoder or dial reads 0° when the center unit is oriented so that the sighting axis 170 is oriented upwards towards the zenith, or more generally so that the sighting axis 170 is parallel to the second axis 150, the sighting axis 170 corresponds to the axis that is strictly orthogonal to the second axis 150 when the center unit 110 is oriented relative to the alidade 120, so that according to the reading of the dial provided on the total station or the encoder associated with the rotation of the center unit 110 around the first axis 130, the angle between the second axis 150 and the sighting axis 170 should be 90°. In other words, the sighting axis 170 corresponds to a position where the rotation angle of the center unit around the first axis 130 is 90° (0° corresponds to the sighting axis 170 being parallel to the second axis 150). As Figure 1A As shown, an optical axis 190 associated with the measuring device of the central unit may deviate from the sighting axis 170 by a vertical alignment error 180 .

[0083] Figure 1BA similar type of error is shown, which is called a (horizontal) collimation error. This horizontal collimation error represents the angle 280 between the optical axis 290 of the measuring device associated with the measuring channel of the central unit 110 and the sighting axis 170 when the total station should be set so that the sighting axis 170 is orthogonal to the first axis 130. It should be understood that Figure 1B All other elements of the total station 100 shown in FIG. Figure 1A The elements of the total station 100 described are the same.

[0084] Therefore, the optical axis (or measuring axis) of the measuring device associated with the measuring channel of the central unit 110 may deviate from the sighting axis 170 by a vertical and / or horizontal collimation error. Hereinafter, this will be collectively referred to as collimation error, which may include horizontal and vertical components.

[0085] Figure 1C Shown with reference Figure 1A and Figure 1B The total station 300 is identical to the total station 100 described above. The total station 300 comprises a central unit 310 rotatably mounted on an alidade 320 which is itself rotatably mounted on a base (e.g., Figure 1A and Figure 1B shown). Figure 1C The central unit is shown around the first axis and the second axis ( Figure 1C The aiming axis 370 is determined by the rotation of the first axis (not shown). In this example, the aiming axis 370 is positioned orthogonal to the first axis and the second axis. Figure 1C Also shown are the optical axis 390a of the measuring device associated with the measuring channel of the center unit 310 in the first plane (i.e., the center unit is oriented in a first direction determined by the rotation around the first axis and the second axis) and the optical axis 390b of the same measuring device associated with the same measuring channel in the second plane, in which the center unit 310 is rotated 180° around each of the first axis and the second axis of the total station compared to the first plane, as indicated by the dashed arrows 392 and 394.

[0086] If you will refer to Figure 3A 、 Figure 3B and Figure 4 As further explained, the alignment error of the measurement channel relative to the sighting axis of the total station can be obtained by performing a first measurement on the first face (F1) of the total station and a second measurement on the second face (F2) of the total station. In the absence of any alignment error, the optical axes 390a and 390b will coincide. However, if Figure 1C As shown, in the presence of collimation errors, the optical axes 390a and 390b point in different directions.

[0087] Reference Figure 2, describing a central unit of a total station according to some embodiments.

[0088] Figure 2 is a schematic diagram of a central unit comprising multiple measurement channels. Figure 2 The central unit 210 (eg, referring to Figure 1A-1C The interior of the central unit 110 and 310) is described.

[0089] The central unit 210 includes a housing 235 having an eyepiece 218 at one end and an objective lens (or front lens) 225 at the other end. The central unit 210 includes a plurality of measuring devices, or devices that assist a surveyor in performing measurements, such as an EDM unit 214, a first camera 212 for capturing images of a scene or surroundings of the central unit 210, a second camera 216 for tracking a target, and a reticle arranged in front of the eyepiece 218 or along an optical path provided by the eyepiece 218. Hereinafter, the reticle and the eyepiece will generally be indicated by the reference numeral 218. Figure 2 As shown, the central unit also includes multiple other optical elements, such as splitters, reflectors, etc. (for example, lenses or filters) to provide an optical path between the objective lens 225 of the central unit 210 and each of the measuring devices 212, 214, 216 and 218, thereby providing multiple measurement channels within the central unit 210.

[0090] For example, an optical path for light arriving through objective lens 225 may be established within central unit 210 by redirecting light of a first wavelength (or a first wavelength range) to second (tracker) camera 216 via first beam splitter 211, redirecting light of a second wavelength (or a second wavelength range) to EDM unit 214 via mirror 217 via second beam splitter 213, and redirecting light of another wavelength range to first camera 212 via third beam splitter 215. Reticle 218 may be aligned with the optical axis of objective lens 225. As shown in FIG. Figure 1A-1C As explained, it should be understood that reticle 218, and similarly any optical axes of EDM unit 214, first camera 212, and second camera 216, may be offset from the aiming axis of the center unit as determined by the rotation angle of the center unit about the first and second axes.

[0091] although Figure 2 Four example measuring devices are shown in FIG, but the central unit may include more or less than four measuring devices. For example, the central unit may also include a laser pointer. In addition, Figure 2 The optical arrangement and position of the measurement device shown in FIG are for illustration purposes only and are therefore schematic. The measurement device can be arranged differently and other optical elements (such as filters) can be added to provide different optical paths and thus different measurement channels.

[0092] Figure 3A and Figure 3B Determining the collimation error relative to the sighting axis of the total station for a measurement channel of a total station, more specifically for a measurement channel associated with a camera, is shown.

[0093] Figure 3A An optical arrangement of a plurality of measuring devices of a central unit 311 is shown, which central unit 311 may be equivalent to the central units 110 , 310 and 210 described with reference to the embodiments shown in the previous figures.

[0094] Figure 3A Also shown are the light paths from the EDM unit 314, the first camera 312, the second camera 316 and the reticle (arranged near the eyepiece 318) to the objective lens (or front lens) 325 of the central unit 311. In this example, the central unit 310 is rotated so that an image of a portion of the town including the church tower can be captured. As already described above with respect to Figure 1C As described, a first image can be captured on a first plane (also referred to as F1), and a second image can be captured on a second plane (also referred to as F2), wherein, in the second plane, the center unit is rotated 180° around each of the first axis and the second axis of the total station compared to the first plane.

[0095] Figure 3B The figure shows a superposition of two images captured by, for example, camera 312, on the first and second sides. As can be seen, the position of the church tower in the image captured on the first side deviates from the position of the church tower in the image captured on the second side, indicating a deviation (or misalignment) of the camera's optical axis relative to the aiming axis of the center unit. This deviation therefore represents a collimation error of the camera's optical axis relative to the aiming axis.

[0096] exist Figure 3B In the example, the value "0" indicates where the top of the church tower should be placed if the camera's optical axis is collimated (i.e., corresponds to the sighting axis). In this example, the camera's optical axis appears to have a horizontal collimation error, which can be based on determining the church tower (e.g., Figure 3A The distance between the two identical image points is determined by half the distance between the top of the church tower shown.

[0097] Thus, using this process a determination of the absolute collimation error of the measurement channel associated with camera 312 can be obtained. Figure 3A and Figure 3B The example shows the determination of the absolute collimation error of a measurement channel of a central unit associated with a first camera, but the same procedure can be used to determine the absolute collimation errors of other measurement channels.

[0098] Figure 4Determining the absolute collimation error of a reticle, for example, a centering unit, is shown. As described above, the process is essentially the same as that described above for a camera, in that a surveyor (or operator of a total station) can look through the eyepiece and place the reticle (or crosshairs) seen in the eyepiece on, for example, the top of a church tower. The operator can then rotate the alidade and centering unit 180 degrees about the first and second axes (i.e., the trunnion and vertical axes, respectively) (or can initiate / cause rotation of the alidade) and then look through the eyepiece again. If the reticle is correctly aligned (i.e., there is no collimation error relative to the aiming axis), the center of the reticle (or crosshairs) remains at the top of the church tower. If the top of the church tower is displaced relative to the center of the crosshairs, there is a collimation error, which can be determined based on the vector between the top of the church tower and the origin represented by the center of the crosshairs.

[0099] The same process applies to the EDM unit and the second camera used to track the target. In the latter case, the total station can be operated to lock on a fixed target in the first plane, while the center unit can be operated in the second plane to lock on the same target. If the center unit is rotated exactly 180° around the first and second axes, there is no collimation error. However, if the center unit needs to be rotated 180.2° around one of the axes, the collimation error relative to that axis is 0.1°.

[0100] In principle, this process can be performed for all measuring devices of the central unit, i.e. all measuring channels, to obtain a calibration of all measuring channels relative to the sighting axis of the central unit of the total station. However, this process is time-consuming and requires sighting of far-field objects.

[0101] Embodiments of an improved method for calibrating a measurement channel of a total station are described with reference to the following figures.These embodiments do not require determining an absolute collimation error for each of a plurality of measurement channels of a total station.

[0102] Figure 5A Determining the relative collimation error between a measurement channel associated with a camera and another measurement channel, such as a measurement channel associated with an EDM unit, is shown.

[0103] Figure 5A 5 shows a total station 500, which includes a central unit 510 rotatably mounted on an alidade 520 of the total station 500. The alidade 510 may be rotatably mounted on a base 540 of the total station 500. Figure 5AAs shown, to determine the relative alignment error between the measurement channel associated with camera 512 and the measurement channel associated with EDM unit 514, the center unit is rotated to a predetermined position. In this example, this position corresponds to the center unit being turned downward, with the center unit's objective lens 525 positioned in front of optical element 505, which in this embodiment is a retroreflector or prism. In other words, if the center unit is oriented so that the encoder or scale of the total station reads 0° when the aiming axis is oriented upward and pointing toward the zenith, the center unit of the total station is rotated 180° about the first axis 130, pointing toward the ground (opposite to the zenith). It should be understood that this particular rotation angle is provided as an example only, and that the predetermined position may require a different rotation angle depending on the position of optical element 505 on the alidade or base of the total station. It should also be understood that this process differs from the Face 1 / Face 2 (F1 / F2) process described above for determining the absolute alignment error of one of the measurement channels. Furthermore, the predetermined position may be preconfigured such that the processing unit of the total station is configured to rotate the center unit around the first axis in order to automatically reach the predetermined position for performing calibration.

[0104] like Figure 5A As shown, in this position, a collimated calibration beam 507 enters the central unit 510 through the objective lens 525 and propagates toward the camera 512. In the present case, the collimated calibration beam originates from the light source (or emitter) of the EDM unit 512. In other words, the EDM unit 512 emits a beam 506 toward the objective lens 525 of the central unit, and the beam becomes collimated when passing through the objective lens 525. The collimated beam 506 is reflected by the retroreflector 505 disposed at (or attached to) the alidade 520 and re-enters the central unit 510 through the objective lens 525 to further propagate toward the camera 512. It should be understood that the retroreflector 505 can be disposed at other locations in the alidade, and in some embodiments, it can be attached to the base 540 or another part of the total station, as long as there is an optical path, or more precisely, a line of sight, between the retroreflector 505 and the objective lens 525 of the total station 500.

[0105] Figure 5B An example of a retroreflector is shown in more detail. A retroreflector is an optical component that reflects a collimated light beam so that the path of the reflected light beam is parallel to the path of the incident collimated light beam. As can be seen, the light beam originating from EDM unit 514 is reflected at optical element 505, thereby propagating toward camera 512 of total station 500 as a beam parallel to the original light beam.

[0106] The camera 512 may then capture an image. The above process may be performed for different measurement channels of the central unit, whether for the same predetermined position or different predetermined positions of the central unit, as will be further described below, and one or more images may be captured by the camera 512.

[0107] Figure 6 An example of an image captured by camera 512 is shown in , where image points or light spots representing collimated calibration light beams for multiple channels are shown.

[0108] Figure 6 An image 600 is shown in which a first light spot 601 may correspond to an image point of the collimated calibration beam 507 associated with a measurement channel associated with the EDM unit 514, as described, for example, with reference to Figure 5. The image 600 may also include further image points 602 and 603 representing further measurement channels.

[0109] The relative alignment error between the measurement channel associated with the camera 512 and the measurement channel associated with the EDM unit 514 can then be determined based on the position of the image point 601 in the image 600. In particular, Figure 6 The vector between the origin 610 of the axis represented in (which may correspond to the center of the camera's image sensor or, alternatively, to the coordinates of the aiming axis derived from external F1 / F2 measurements) and the image point 601 represents the collimation error between the two measurement channels. Figure 6 As shown, the collimation error or the vector representing the collimation error may include a vertical component ΔV A and the horizontal component ΔH A The position (or coordinates) of the image point 601 can be obtained by calculating the center of gravity of the pixel corresponding to (the image of) the collimated calibration beam in the captured image.

[0110] Assume (for example, using the Figure 1C 、 Figure 3A and Figure 3B If the measurement channel associated with camera 512 is calibrated relative to the sighting axis using the aforementioned process, the absolute collimation error of the measurement channel associated with EDM unit 514, i.e., the collimation error relative to the sighting axis of the total station, can be determined based on the determined relative collimation error. The same determination can be made for the other measurement channels corresponding to image points 602 and 603.

[0111] Figure 7 A general overview of a method 7000 of calibrating a total station (such as any of the total stations described herein) (such as any of the total stations described with reference to the previous and following figures) is shown.

[0112] At 7100, a collimation error is determined for any one of a plurality of measurement channels of the total station relative to a sighting axis of the total station, thereby providing a calibrated reference measurement channel. The collimation error may be determined by any process, for example, by using a method as described above with reference to Figure 1C 、 Figure 3A 、 Figure 3B and Figure 4 The process of measuring in the first surface and the second surface is determined.

[0113] At 7200, the central unit of the total station is rotated about at least the first axis to a predetermined position in which the collimated calibration beam enters the central unit through the objective lens of the central unit to propagate further toward the camera. This corresponds to, for example Figure 5A The process is shown in , where the center unit is rotated into a downward orientation.

[0114] The collimated calibration beam can then be associated with one of the following: (i) at least one measurement channel to be calibrated, if the calibrated reference measurement channel is a measurement channel associated with the camera; or (ii) a calibrated reference measurement channel, if the calibrated reference measurement channel is a measurement channel other than a measurement channel associated with the camera. Figure 5A , which means that the measurement channel associated with the EDM unit 514 can correspond to a calibrated reference measurement channel (in this case, the measurement channel associated with the camera is the measurement channel to be calibrated), or the measurement channel associated with the EDM unit 514 can be a measurement channel to be calibrated relative to the measurement channel associated with the camera (in this case, the measurement channel associated with the camera is the calibrated reference measurement channel).

[0115] At 7300, at least one image is captured with a camera, wherein the collimated calibration beam is detectable in the image, e.g. Figure 6 shown.

[0116] At 7400, based at least on the position of an image point in the captured image(s) corresponding to the collimated calibration beam (also referred to as Figure 6 ), determining a relative collimation error between the measurement channel associated with the camera and another measurement channel. As described above, the other measurement channel can be the measurement channel to be calibrated (if the calibrated reference measurement channel is the measurement channel associated with the camera) or a calibrated reference measurement channel (if the calibrated reference measurement channel is a measurement channel other than the measurement channel associated with the camera).

[0117] Figure 8A Determining the relative collimation error between a measurement channel associated with a first camera and a measurement channel associated with a second camera using an external light source is shown.

[0118] The total station 800 is equivalent to any of the total stations described above with reference to the aforementioned figures, except that in this embodiment, the total station is equipped with an optical element 805, which includes a light source for providing a collimated calibration beam 806 when the central unit 810 is rotated to a predetermined position, and the collimated calibration beam 806 enters the central unit via the front lens 825 of the central unit 810.

[0119] like Figure 8A As shown, the collimated calibration beam can be provided by an optical element 805, which includes a light source 805a, the light emitted by which is reflected by a beam splitter or a reflector 805b, passes through a collimating lens 805c, and then reaches the objective lens or front lens 825 of the total station 800. The optical element 805 can be placed in the collimator 820 of the total station 800.

[0120] Alternatively, if Figure 8B As shown, a collimated calibration beam can be provided by an optical element 895, which includes two light sources 895a placed behind a pinhole or diffuser (or negative crosshairs) 895b. Each light source 895a can emit light of a specific wavelength. The optical element 895 can, for example, include a plate 895b with a small opening so that a divergent beam is formed downstream of the pinhole. The beam can then be collimated by a lens 895c of the optical element 895. In this case, the optical element 895 can serve as a collimator 895 for the calibration beam.

[0121] All other elements of the total station 800 are identical to those described above with reference to the total station shown in the preceding figures. This includes, for example, a first camera 812, a reticle (or eyepiece) 818, and a second camera 816, which are arranged in the central unit 810 of the total station 800. An alidade 820 is also mounted on the base 840 and the tripod, as shown in FIG. Figure 1A and Figure 1B shown.

[0122] Furthermore, the collimated beam may include light of a first wavelength (e.g., visible light) to which the first camera 812 is sensitive, and light of a second wavelength (e.g., light having a wavelength of approximately 800-900 nm (e.g., 850 nm)) to which the second camera 816 is sensitive. From the perspective of the first camera 812 and the second camera 816, the collimated calibration beam originates from Figure 8A and Figure 8B Optical elements 805 and 895 are shown providing the same optical position.

[0123] Generally, the first camera 812 may be configured to capture images within a first wavelength range, and the second camera 816 may be configured to capture images within a second wavelength range.

[0124] As described in the previous embodiment, if the calibrated reference measurement channel is the measurement channel associated with the first camera 812, the measurement channel associated with the second camera 816 can be the measurement channel to be calibrated, or it can be the calibrated reference measurement channel (in this case, other measurement channels including the measurement channel associated with the first camera can be calibrated).

[0125] Still refer to Figure 8A , at least one image 816 ′ of the collimated calibration beam is captured with the second camera 816 , and at least one image 812 ′ of the collimated calibration beam is captured with the first camera 812 , wherein the collimated calibration beam is detectable in these images. Figure 8C A possible example of such an image is shown in .

[0126] The relative collimation error between the measurement channel associated with the first camera 812 and the measurement channel associated with the second camera 816 can then be determined based on a comparison between the positions of the image points corresponding to the collimated calibration beam in the image captured by the first camera 812 and the positions of the image points corresponding to the collimated calibration beam in the image captured by the second camera 816. This is determined by Figure 8C The two images shown in FIG. 5 show that the collimated calibration light beam generates image points (or light spots) at different positions in the images captured by the first camera and the second camera.

[0127] Even if the first camera and the second camera are sensitive to the same wavelength range, and even if the first wavelength is the same as the second wavelength, the same process can be used as long as both the first camera 812 and the second camera 816 can detect the collimated calibration beam of that particular wavelength.

[0128] Reference Figure 9 , another embodiment for obtaining the relative collimation error between measurement channels associated with two different cameras is described.

[0129] Figure 9 Shows something like Figure 8A The situation shown is the same except that the collimated light beam does not originate from an optical element (or light source) arranged at the alidade 920 of the total station 900, but rather from a light source of one of the plurality of measuring devices of the central unit 910. In this example, the light source of the EDM unit 914 can be used to emit the collimated light beam toward the front lens 925 of the central unit 910 of the total station 900, thereby becoming a collimated collimated light beam. The alidade 920 can then be equipped with an optical element 905, such as a retroreflector (e.g., as shown in FIG. Figure 5B925 ), at which optical element 905 the calibration beam originating from the EDM unit 914 (which was collimated by the front lens 925 upon leaving the center unit) is reflected to re-enter the center unit 920 through the front lens 925 for further propagation toward the first camera 912 and the second camera 916. It will be appreciated that, as described above, the optical element or retroreflector 905 is located at the alidade 920 or base 940 of the total station such that it is located in front of the front lens or objective 925 when the center unit 920 is rotated to a predetermined position where calibration is to be performed.

[0130] With respect to the present embodiment, the collimated light beam originating from the EDM unit 914 (or laser pointer) is detectable at both the first camera 912, which is sensitive to visible light, and the second camera 916, which is sensitive to light in the range of, for example, 800 nm to 900 nm. Thus, in the present embodiment, the measurement channels associated with the second camera 916 can be calibrated relative to the measurement channels associated with the first camera 912, and the measurement channels associated with the EDM unit can be calibrated relative to the measurement channels associated with the second camera 916 (or relative to the measurement channels associated with the first camera 912).

[0131] Figure 9 It is also shown that the position of the collimated calibration beam in the first image 912' captured by the first camera 912 may deviate from the position of the collimated calibration beam in the second image 916' captured by the second camera 916, thereby indicating that there is a collimation error between the measurement channel associated with the first camera 912 and the measurement channel associated with the second camera 916. Figure 9 A closer view of the reflector 905 arranged at the collimator 920 of the total station 900 (or attached to the collimator 920 of the total station 900) is also provided, wherein the incident light beam 906 received from the EDM unit 914 and the light beams 907, 908 reflected back to the objective lens 925 of the central unit 910 of the total station 900 are further propagated toward the first camera 912 and the second camera 916, respectively.

[0132] Reference Figure 10 , describing the determination of a relative collimation error between a measurement channel associated with a first camera and a measurement channel associated with a graticule of a central unit of a total station.

[0133] The principle is generally similar to that for calibrating the other measurement channels described above with reference to the previous figures, with the difference that in this case the collimated calibration beam entering the objective (or front lens) 1025 does not originate from a light source placed in front of the objective 1025 of the central unit 1010, nor from a light source located inside the central unit 1010, but rather from a light source that emits a beam that enters the central unit 1010 through the eyepiece 1018 of the central unit 1010 of the total station 1000. This beam 1006 can then propagate within the central unit 1010 to become collimated (through the optics of the central unit 1010), exit the objective 1025, and then be reflected at an optical element 1005 (e.g., a retroreflector of an alidade attached to the total station) before re-entering the central unit 1010 as a collimated beam 1007.

[0134] It should be understood that the light emitted from the external light source 1050 does not need to be collimated. The light source can be, for example, a light source provided at a protective bag or protective housing of the total station. As another alternative, the light source can be provided at the handle of the alidade.

[0135] Furthermore, it should be understood that, in order to determine the relative collimation error between the measurement channels associated with the camera or another camera, as an alternative to the solution described with reference to the previous figures, the initial beam can also come from a light source external to the total station (or external to the central unit), so that the initial beam enters the central unit through the eyepiece of the central unit. Nevertheless, as described above, the collimated beam is redirected towards the camera by re-entering the central unit through the objective lens of the central unit and by retroreflection via an optical element (such as a retroreflector).

[0136] It should also be understood that while the present invention provides embodiments in which relative alignment errors can be determined for multiple measurement channels when the center unit is rotated to a single predetermined position and a single collimated calibration beam is used, the center unit can also be rotated to different predetermined positions. Furthermore, multiple collimated calibration beams can also be used.

[0137] For example, after determining the relative collimation error between the first measurement channel and the measurement channel associated with the camera when the center unit is rotated to a first predetermined position, the relative collimation error between the measurement channel associated with another measurement device and the measurement channel associated with the camera can be determined by rotating the center unit at least about the first axis to another predetermined position (at which another collimated calibration beam enters the center unit through the objective lens to further propagate toward the camera). The other collimated calibration beam can then be correlated with the measurement channel associated with the other measurement device. The relative collimation error between the measurement channel associated with the camera and the measurement channel associated with the other measurement device can then be determined based at least on the position of an image point corresponding to the other collimated calibration beam in an additional image captured by the camera.

[0138] refer to Figure 11 , describes another embodiment using multiple collimated beams at a single predetermined location.

[0139] Figure 11 A total station 1100 is shown, which is equivalent to a reference Figure 9 The total station 900 (and the scenario) is described except that instead of having only one calibration beam 1106 originating from the EDM unit 1114 (corresponding to Figure 9 The light beam 906 of the EDM unit 914 is irradiated to the retroreflector 1105 (corresponding to Figure 9 Instead of a reflector 905 in the image sensor, there is an additional calibration beam 1109a originating from another device (e.g., a laser pointer 1199).

[0140] like Figure 11 As shown, in this example, the light source of the laser pointer 1199 can be used to emit an additional calibration beam towards the front lens 1125 of the central unit 1110 of the total station 1100. The collimator 1120 can then be equipped with an optical element 1105, such as a retroreflector (e.g., as shown in FIG. Figure 5B 11) at which the calibration beam originating from the laser pointer 1199 is reflected to re-enter the central unit 1120 through the front lens 1125 for further propagation toward the first camera 1112. It should be understood that, as described above, the optical element or retroreflector 1105 is located at the alidade 1120 or base 1140 of the total station so that when the central unit 1120 is rotated to a predetermined position where calibration is to be performed, the optical element or retroreflector 1105 is located in front of the front lens or objective 1125.

[0141] In this embodiment, first calibration beam 1106 is emitted from EDM unit 1114 and detected at first camera 1112 and second camera 1116, thereby enabling relative calibration of collimation errors between measurement channels associated with EDM unit 1114, first camera 1112, and second camera 1116. Images 1112' and 1116' captured by the first and second cameras, respectively, illustrate that the first calibration beam is detectable in both images. Furthermore, second calibration light 1109a emitted from laser pointer 1199 and detected at first camera 1112 enables relative calibration of collimation errors between measurement channels associated with laser pointer 1199, first camera 1112, and EDM unit 1114 because first calibration beam 906 and second calibration beam 1109a (reflected at optical element 1105 as beams 1107 and 1109b) are detectable in image 1112' captured by first camera 1112. Thus, if the (absolute) collimation error of at least one of the measurement channels relative to the sighting axis is known, the collimation error associated with each of the measurement channels relative to the sighting axis of the total station can be determined.

[0142] To this end, the total station may then comprise a first optical element attached to the alidade or base to provide a first collimated calibration beam when the central unit is rotated to a first predetermined position, and a second optical element attached to the alidade or base to provide a second collimated calibration beam when the central unit is rotated to a second predetermined position.

[0143] Furthermore, it should be understood that the determination of the relative alignment error between at least two measuring channels of the total station may be automatic, since the processing unit, e.g. Figure 10 The processing unit 1098, schematically shown in FIG, is configured to determine or obtain a collimation error of any one of the plurality of measurement channels relative to the sighting axis of the total station, and then rotate the central unit about at least a first axis to a predetermined position in which a collimated calibration beam emitted or reflected from an optical element attached to the alidade or base enters the central unit for further propagation toward the camera. The control unit may also be configured to capture an image with the camera and determine a relative collimation error between a measurement channel associated with the camera and another measurement channel associated with another measurement device other than the camera.

[0144] It should be understood that, unless explicitly stated otherwise, the examples shown in different figures may be combined, and elements with the same reference numerals in different figures may be the same or similar to each other. In any case, the above description is not intended to limit the scope of the present invention, which is limited only by the scope of the appended claims.

Claims

1. A method (7000) of calibrating a total station (100, 500), the total station comprising a central unit (510) mounted on an alidade (520) for rotation about a first axis (130), wherein: The alidade is mounted on a base (540) of the total station for rotation about a second axis (150) orthogonal to the first axis, such that a sighting axis (170) of the total station can rotate about a rotation point, wherein the central unit comprises a plurality of measurement channels, wherein the measurement channels are associated with measurement devices (512, 514, 518) having optical axes, and wherein at least one measurement device is a camera (512) configured to capture an image, the method comprising: determining (7100) a collimation error relative to the sighting axis for any one of the plurality of measurement channels, thereby providing a calibrated reference measurement channel; rotating (7200) the central unit at least about the first axis to a predetermined position in which a collimated calibration beam enters the central unit through an objective lens of the central unit for further propagation towards the camera, wherein the collimated calibration beam is associated with: (i) at least one measurement channel to be calibrated if the calibrated reference measurement channel is a measurement channel associated with the camera, or (ii) with the calibrated reference measurement channel if the calibrated reference measurement channel is a measurement channel other than a measurement channel associated with the camera; capturing (7300) at least one image with the camera, wherein the collimated calibration beam is detectable in the at least one image; and Based at least on the position of an image point corresponding to the collimated calibration beam in the at least one captured image, determine (7400) the following relative collimation error: if the calibrated reference measurement channel is a measurement channel associated with the camera, determine the relative collimation error between the measurement channel associated with the camera and the at least one measurement channel to be calibrated; or if the calibrated reference measurement channel is a measurement channel other than the measurement channel associated with the camera, determine the relative collimation error between the measurement channel associated with the camera and the calibrated reference measurement channel.

2. The method according to claim 1, wherein Determining the collimation error of the reference measurement channel relative to a sighting axis of the total station includes aiming the center unit toward a far-field object.

3. The method according to claim 1 or 2, wherein: Determining the alignment error of the reference measurement channel relative to the aiming axis of the total station includes performing a first measurement on a first face of the total station and performing a second measurement on a second face of the total station, wherein, in the second face, the center unit is rotated 180° around each of the first axis and the second axis of the total station compared to the first face.

4. A method according to any one of the preceding claims, wherein The camera is any one of a camera configured to capture an image of a scene around the total station and a camera configured to track a target by the total station.

5. A method according to any one of the preceding claims, wherein If the calibrated reference measurement channel is a measurement channel associated with the camera, the at least one measurement channel to be calibrated includes a measurement channel associated with a measuring device comprising a light source, or if the calibrated reference measurement channel is a measurement channel other than a measurement channel associated with the camera, the calibrated reference measurement channel includes a measurement channel associated with a measuring device comprising a light source, and wherein the collimated calibration light beam originates from the light source and enters the central unit by retroreflection on an optical element of the alidade or the base attached to the total station.

6. The method according to claim 5, wherein: The measuring device including the light source is one of a laser pointer and an electronic distance measuring device.

7. A method according to any one of the preceding claims, wherein the camera being a first camera configured to capture images within a first wavelength range, and wherein, if the calibrated reference measurement channel is a measurement channel associated with the first camera, the at least one measurement channel to be calibrated comprises a measurement channel associated with a second camera configured to capture images within a second wavelength range, or if the calibrated reference measurement channel is a measurement channel other than a measurement channel associated with the first camera, the calibrated reference measurement channel comprises a measurement channel associated with a second camera configured to capture images within a second wavelength range, wherein the collimated calibration beam comprises light of a first wavelength within the first wavelength range and light of a second wavelength within the second wavelength range, The method further comprises: capturing at least one image of the collimated calibration beam with the second camera, wherein the collimated calibration beam is detectable in the at least one image, and Wherein, determining the relative collimation error comprises comparing the position of an image point corresponding to the collimated calibration beam in the at least one image captured by the first camera and the position of an image point corresponding to the collimated calibration beam in the at least one image captured by the second camera.

8. The method according to claim 7, wherein: The first wavelength is the same as the second wavelength.

9. The method according to claim 7 or 8, wherein The first wavelength range is the same as the second wavelength range.

10. The method according to any one of claims 7 to 9, wherein The collimated calibration light beam originates from a light source of one of the plurality of measuring devices and enters the central unit by retroreflection of an optical element of the alidade or the base attached to the total station, or The collimated calibration beam originates from a beam entering the central unit through the eyepiece of the total station, propagates toward the optical element of the collimator or the base attached to the total station, and then re-enters the central unit through retroreflection of the optical element.

11. The method according to claim 7, when claim 7 refers to any one of claims 1 to 4, wherein: The first wavelength is different from the second wavelength, and / or wherein the first wavelength is in the visible wavelength range and the second wavelength is in the range of 800 nm-900 nm.

12. A method according to any one of claims 7 to 9 and 11, when claim 7 refers to any one of claims 1 to 4, wherein The collimated calibration beam originates from a light source attached to the alidade or the base of the total station; or The collimated calibration beam originates from a beam entering the central unit through the eyepiece of the total station, propagates toward the optical element of the collimator or the base attached to the total station, and then re-enters the central unit through retroreflection of the optical element.

13. A method according to any one of the preceding claims, wherein If the calibrated reference measurement channel is a measurement channel associated with the camera, the at least one measurement channel to be calibrated includes a measurement channel associated with the graticule of the central unit of the total station, or if the calibrated reference measurement channel is a measurement channel other than the measurement channel associated with the camera, the calibrated reference measurement channel includes a measurement channel associated with the graticule of the central unit of the total station, and wherein the collimated calibration beam originates from a beam entering the central unit of the total station through the measurement channel associated with the graticule of the central unit, propagating toward an optical element of the collimator or the base attached to the total station, and then re-enters the central unit by retroreflection of the optical element.

14. The method according to claim 13, wherein The light beam entering the central unit of the total station through a channel associated with the reticle of the central unit is not collimated.

15. The method of any one of the preceding claims, further comprising performing a relative calibration between a measurement channel associated with another measurement device and a measurement channel associated with the camera by: rotating the central unit at least about the first axis to another predetermined position, in which another collimated calibration light beam enters the central unit through the objective lens of the central unit to propagate further towards the camera, wherein said another collimated calibration beam being associated with said measurement channel associated with said another measurement device; capturing at least one additional image with the camera, wherein the another collimated calibration beam is detectable in the at least one additional image; and Based at least on the position of the image point corresponding to the further collimated calibration beam in the at least one additional image, a relative collimation error between a measurement channel associated with the camera and a measurement channel associated with the further measurement device is determined.

16. The method according to claim 15, wherein The total station includes: a first optical element attached to the alidade or the base, for providing a first collimated calibration beam when the central unit is rotated to the predetermined position; and a second optical element attached to the alidade or the base, for providing a second collimated calibration beam when the central unit is rotated to the other predetermined position.

17. A total station (100, 500), comprising: a center unit (510) mounted on the alidade (520) for rotation about a first axis (130), a base (540) on which the alidade is mounted to rotate about a second axis (150) intersecting the first axis so that the sighting axis (170) of the total station can rotate about a rotation point, wherein the central unit comprises a plurality of measurement channels, wherein the measurement channels are associated with measurement devices (512, 514, 518) having optical axes, wherein at least one measurement device (512) is a camera configured to capture an image, at least one optical element (505) attached to the alidade or the base, and A processing unit (1098) is configured to perform calibration of the total station by: determining a collimation error relative to the sighting axis for any one of the plurality of measurement channels, thereby providing a calibrated reference measurement channel; rotating the central unit at least about the first axis to a predetermined position in which a collimated calibration light beam emitted or reflected at the optical element enters the central unit through an objective lens of the central unit for further propagation toward the camera, wherein the collimated calibration light beam is associated with: (i) at least one measurement channel to be calibrated if the calibrated reference measurement channel is a measurement channel associated with the camera, or (ii) with the calibrated reference measurement channel if the calibrated reference measurement channel is a measurement channel other than a measurement channel associated with the camera; causing the camera to capture at least one image, wherein the collimated calibration beam is detectable in the at least one image; and Based at least on the position of an image point corresponding to the collimated calibration light beam in the at least one captured image, the following relative collimation error is determined: if the calibrated reference measurement channel is a measurement channel associated with the camera, the relative collimation error between the measurement channel associated with the camera and the at least one measurement channel to be calibrated is determined; or if the calibrated reference measurement channel is a measurement channel other than the measurement channel associated with the camera, the relative collimation error between the measurement channel associated with the camera and the calibrated reference measurement channel is determined.

18. The total station according to claim 17, wherein: The control unit is configured to perform the method according to any one of claims 2-16.

19. The total station according to claim 17 or 18, wherein: The at least one optical element includes at least one of the following: a retroreflector that reflects light emitted from a light source of a measuring device among the plurality of measuring devices when the central unit is rotated to a first predetermined position; and a light source for emitting a collimated calibration light beam having a first wavelength and a second wavelength.

Images