Position measuring device, position measuring system, position measurement method, and computer program product

Abstract

The invention relates to a position measuring device (10) for measuring a position (P) of an object (12) at a construction site (14), for example a building construction site or a civil engineering construction site, the position measuring device comprising at least one camera (16, 18, 20, 22, 24, 26), wherein the position measuring device (10) has at least one camera pair consisting of at least two cameras (16, 18, 20, 22, 24, 26), and wherein the device is designed to automatically correct and / or mathematically compensate for a tilt angle error (NF) between the cameras (16, 18, 20, 22, 24, 26) of at least one camera pair, in particular to limit said error to a maximum of 0.3 pixels. The invention enables particularly cost-effective and precise measurements of positions at construction sites.

Description

[0001] Position measuring device, position measuring system, method for position measurement and computer program product

[0002] Description

[0003] The invention is based on a position measuring device for measuring the position of an object on a construction site. The position measuring device has at least one camera. Such position measuring devices, for example in the form of total stations, are used on construction sites to transfer positions marked on construction plans to the construction site, to mark positions on the construction site at corresponding positions in the construction plans, or to compare positions on the construction site with corresponding positions in the construction plans.

[0004] A total station typically features a laser-based distance meter. The distance meter is coupled to high-resolution angle sensors. Its beam direction is adjustable. The distance meter can be used to locate a target position on the construction site and measure the distance to that target position. The angle sensors also allow the beam direction of the distance meter's laser to be determined. This allows the target position to be measured relative to the total station's body-based coordinate system.

[0005] Total stations often also have a camera. This camera may include a telephoto lens, for example. This allows the camera to view the target position in a magnified view, for example. It can also be used to verify that the distance meter is actually hitting the target position with its laser beam.

[0006] In order to determine the coordinates of the target position in a coordinate system independent of the total station, for example, a coordinate system used in the construction plan, the total station itself must first be calibrated separately using calibration markings measured on the construction site. In particular, a mapping of the total station's own coordinate system to the independent coordinate system must be determined. Measurement errors of up to 5 mm are typically acceptable when measuring positions on construction sites. In order for the total station to maintain this measurement error tolerance, very high accuracy requirements must be placed on the angle sensors and the mechanical stability of the total station as a whole.

[0007] Due to the high accuracy requirements, total stations are very expensive and complex to manufacture.

[0008] The object of the present invention is therefore to provide devices and methods that enable a cost-effective way of precisely measuring positions on construction sites.

[0009] The object is initially achieved by a position measuring device for measuring a position of an object on a construction site, for example a building construction site or a civil engineering construction site, comprising at least one camera, wherein the position measuring device has at least one camera pair consisting of at least two cameras, and wherein it is configured to automatically correct and / or calculate an inclination angle error between cameras of at least one camera pair, in particular to limit it to a maximum of 0.3 pixels.

[0010] Tilt angle errors correspond to relative rotations of one camera in a camera pair to another camera in the camera pair around an axis connecting the two, so that the two cameras in the camera pair span differently aligned planes due to their viewing directions and their connecting line.

[0011] The position measuring device can be configured to determine the position of the object by evaluating images from the cameras. The cameras can thus be used not only to provide a magnified view of a target region to the user of the position measuring device, but also to provide data for the position measurement itself.

[0012] Surprisingly, our own series of tests showed that, up to a certain extent, tilt angle errors only slightly influence the overall measurement error, especially cumulative measurement errors due to cumulative drift. However, if the tilt angle errors exceed a certain threshold, the measurement error can increase disproportionately. As will be explained in more detail below in connection with Fig. 6, a tilt angle error threshold of approximately 0.3 pixels was found, above which tilt angle errors had a significant impact. For example, increasing the tilt angle error from 0.3 pixels to 0.5 pixels led to a sixfold increase in the error, i.e., the cumulative drift.

[0013] For a field of view with a viewing angle of 90° for a camera that is vertically mapped to 1536 pixels, for example, an error of 0.3 pixels corresponds to an angular error of

[0014] 0.3 pixels x 90° / 1536 pixels = approx. 0.018°.

[0015] One of the reasons for this may be that, for example, SLAM methods are often only able to successfully assign at least some of the elements contained in the evaluated images of the different cameras to one another up to the aforementioned tilt angle error threshold.

[0016] At least one of the cameras can have at least 3 MP. A 1 MP camera can be understood as a camera that has an image sensor with at least 1 million pixels. Accordingly, a 3 MP camera has at least 3 million pixels. The at least six cameras thus have a total of at least 18 million pixels.

[0017] In color cameras, a pixel can correspond to a triple point, i.e., a group of three sensor units of the image sensor for each of the three color components captured, for example, red, green, and blue. In black-and-white cameras, a pixel can correspond to a single sensor unit.

[0018] The cameras can have a field of view that covers at least 135° horizontally, in particular at least 180°, and particularly preferably at least 270°. The field of view can cover at least 90° vertically, in particular at least 135°, and particularly preferably at least 170°. The fields of view of the cameras can overlap at least in pairs, in particular both horizontally and vertically. At least one of the cameras, preferably all cameras, can have an image format corresponding to 3:2, 4:3, 5:4, 16:9, or 16:10. It can correspond to a so-called 4K standard or a higher standard, in particular at least 8K, for example 16K. A higher standard is associated with a higher number of sensor units. A higher number of sensor units, in turn, generally enables higher angular resolutions.

[0019] It's particularly conceivable that the camera is at least a black-and-white camera. A black-and-white camera can offer a high pixel resolution at a reasonable price.

[0020] It is also conceivable that at least one camera has significantly more pixels in one direction than in another. For example, the camera can have at least four times as many pixels horizontally as vertically. The camera can thus be a line scan camera, but one that offers limited resolution in its second dimension. Such a camera can thus offer a particularly high angular resolution in at least one of the two dimensions of its image sensor. Such a camera can also offer a very wide field of view in at least one of the two dimensions while still providing sufficient angular resolution in this dimension.

[0021] The invention is based, among other things, on the surprising finding that the accuracy with which positions can be determined by multiple cameras can depend very nonlinearly on the number of cameras. In particular, there is a range for the number of cameras that leads to an optimum between the achievable accuracy and the manufacturing effort, component costs, and calibration effort.

[0022] This finding as well as further improvements and embodiments are explained in more detail in the following description of the figures.

[0023] The schematic drawing illustrates exemplary embodiments of the invention and explains them in more detail in the following description. They show:

[0024] Fig. 1 a position measuring device in a schematic, perspective view,

[0025] Fig. 2 to Fig. 4 and Fig. 6

[0026] Results of our own series of studies,

[0027] Fig. 5 important sources of measurement errors,

[0028] Fig. 7 shows a position measuring system with a user thereof and Fig. 8 shows a method for measuring a position on a construction site.

[0029] In the following description of the figures, the same reference numerals are used for identical or functionally corresponding elements to facilitate understanding of the invention.

[0030] Fig. 1 shows a schematic, perspective view of a position measuring device 10 for measuring a position P of an object 12 on a building construction site 14. By way of example, the object 12 is a wall of a building. A borehole is drilled into the object 12, i.e. the wall, at position P. The position P is to be measured relative to a coordinate system K. If the position P in the coordinate system K is known, this position can be compared, for example, with planning data from a BIM model (Building Information Model) or a CAD model. Other applications for which the position P in the coordinate system K should be known are also conceivable. In order to be able to establish a reference to the coordinate system K, a plurality of position markings 102 are measured and arranged on the building construction site 14 as calibration points of the coordinate system K.

[0031] The position measuring device 10 has six cameras 16, 18, 20, 22, 24, 26. The cameras 16, 18, 20, 22, 24, 26 are each arranged in pairs on a mount 28. A camera pair with cameras 16, 18 is facing left. A camera pair with cameras 20, 22 is facing forward. A camera pair with cameras 24, 26 is facing right. The cameras together have a resolution of at least 18 MP.

[0032] The cameras 16, 18, 20, 22, 24, 26 are grayscale cameras. It is conceivable that the cameras 16, 18, 20, 22, 24, 26 are color cameras, for example, an RGB camera. In a further embodiment, at least one of the cameras 16, 20, 22, 24, 26 can be configured to record depth information. It can, for example, be a color and depth information camera, for example, an RGBD camera, which enables particularly precise image evaluations, in particular using photogrammetric methods and / or SLAM algorithms. It is also conceivable that it is a more cost-effective grayscale and depth information camera.

[0033] Each camera pair is thus arranged rotated by 90 degrees relative to at least one other camera pair. Thus, at least one of the cameras 16, 18, 20, 22, 24, 26 is arranged on the mount 28 rotated by 90 degrees relative to at least one other of the cameras 16, 18, 20, 22, 24, 26. Furthermore, all cameras 16, 18, 20, 22, 24, 26 are spaced apart from one another.

[0034] Each of the cameras 16, 18, 20, 22, 24, 26 has an autofocus lens. The cameras 16, 18, 20, 22, 24, 26 can thus focus automatically. They can each include a telephoto lens, particularly a motorized one. They can each have at least 3 MP. They can also have a resolution of, for example, at least 2048 x 1536 pixels, particularly with an aspect ratio of 4:3.

[0035] The mount 28 sits on a stand 30. The stand 30 can be height-adjustable. The stand 30 can have vibration damping.

[0036] The position measuring device 10 further comprises a controller 32. The controller 32 comprises a computer, for example, a tablet PC or a smartphone. The controller 32 has, in particular, a memory 34 in which a computer program product 36 is stored in a retrievable and executable manner on the controller 32. The computer program product 36 is configured to measure the position P with the aid of the remaining position measuring device 10, in particular according to the method described in more detail below, particularly with reference to Fig. 8.

[0037] The controller 32 further comprises a gravity direction sensor 38 and an acceleration sensor 40, in particular for detecting vibrations.

[0038] Extensive investigations have been carried out using variants of position measuring devices 10 in which different features have been systematically varied.

[0039] In particular, 10 circular paths with a length of approximately 80 meters were covered using such position measuring devices. For these studies, the computer program product 36 included a SLAM algorithm, for example, ORB-SLAM2 by Raul Mur-Artal et al. or SVO2.0 by Davide Scaramuzza et al., to track the path traveled by the respective position measuring device 10 relative to the starting point.

[0040] For each test run, root-mean-square measurement errors were determined, i.e., the root-mean-square cumulative drift over the entire distance traveled. To determine the measurement errors, comparative measurements were performed using a total station.

[0041] In an initial series of experiments, the extent to which the number of pixels in the cameras' image sensors influences the measurement error was investigated. For this purpose, only two cameras were used instead of six.

[0042] Fig. 2 shows a diagram of the resulting root-mean-square measurement error, measured in mm, for each of the two cameras used, for example, cameras 20 and 22, for different numbers of pixels (given in MP). It can be seen that with this two-camera solution, the total measurement error can be kept within 5 mm if cameras with at least 12 MP each are used.

[0043] Camera pairs with 3 MP each resulted in a root-mean-square measurement error of approximately 1 cm. This means that for a path length reduced to, say, 40 meters or less, the measurement error in the desired range can be expected to be no more than 5 mm.

[0044] In another series of experiments, the influence of the number of cameras used on the measurement error was investigated. Figure 3 shows a graph of root mean square measurement errors, measured in mm, as a function of the number of cameras used. Each camera had a 3 MP image sensor.

[0045] As expected from Fig. 2, two cameras again resulted in a square-mean measurement error of approximately 1 cm.

[0046] Surprisingly, it was found that increasing the number of cameras used significantly reduces the root mean square measurement error up to a number of six cameras.

[0047] However, surprisingly, increasing the number of cameras beyond six results in hardly any significant improvements. In particular, the root mean square measurement error with six cameras was kept well below the required limit of 5 mm.

[0048] Since the manufacturing costs for a position measuring device 10 increase approximately linearly with the number of cameras used, an optimum is in the range of approximately six cameras.

[0049] In a further series of experiments, the influence of the image quality of captured images on the measurement error was investigated. In particular, the effects of exposure time as a measure of possible motion blur, as well as the overall brightness and thus the influence of image noise, were investigated.

[0050] As can be seen from the diagram in Fig. 4, extended exposure times TS lead to an increasing degree of motion blur when the position measuring device 10 moves along the circular path, and thus to significantly increased measurement errors, measured in mm. Even a slight motion blur can double, triple, or even further increase the measurement error.

[0051] In contrast, image noise SNR, measured as signal-to-noise ratio, for example in dB, as long as it is below a certain threshold, influences the achieved measurement error only to a very small, negligible extent.

[0052] The result shows that blurring in the images taken by cameras 16, 18, 20, 22, 24, 26 should be minimized or even avoided as much as possible.

[0053] The blurring can result from movements of the position measuring device 10 and / or from movements of the object 12 to be analyzed, even after individual focusing of the lenses of the cameras 16, 18, 20, 22, 24, 26.

[0054] Movements of the position measuring device 10 can be detected, for example, using the acceleration sensor 40. It is conceivable, for example, to only evaluate recorded images if no vibrations or other movements are detected, or only vibrations and / or other movements of the cameras 16, 18, 20, 22, 24, 26 below a defined movement threshold.

[0055] If the acceleration sensor 40 provides data about the movement, for example a direction of movement and / or a speed of movement, it is also conceivable to calculate out at least one of the recorded images, in particular all recorded images, with regard to the movement and thus to sharpen it.

[0056] It is also conceivable to determine a value for image sharpness directly from the captured images. This is particularly feasible for images of known objects, such as the position markers 102 serving as calibration markers.

[0057] Images that fail to achieve a required level of sharpness can be discarded and / or re-captured. Further analysis can be limited to those images that meet a defined minimum level of sharpness.

[0058] Exposure times can also be limited to avoid motion blur. For example, the exposure time for capturing an image can be set to less than 1 / 500 s, especially less than one millisecond. Based on the results shown in Fig. 4, a (slightly) increased image noise may be acceptable.

[0059] In a further study, the influence of different types of positioning errors of cameras 16, 18, 20, 22, 24, 26 was compared relative to each other.

[0060] For this purpose, images from cameras 16, 18, 20, 22, 24, and 26 were simulated. In particular, the error types shown in Fig. 5—distance error AF, squint angle error SF, and tilt angle error NF—were investigated. Distance errors AF correspond to an unintentional approach or distancing, i.e., unintentional translation, of one of the cameras 16, 18, 20, 22, 24, and 26 from at least one of the other cameras 16, 18, 20, 22, 24, and 26. Squint angle errors SF correspond to an unintentional rotation about the y-axis, such that the two cameras of a camera pair are aligned in mutually non-parallel directions within the plane spanned by their viewing direction and their connecting line. Tilt angle errors NF correspond to unintentional rotations around the x-axis, so that the two cameras of a camera pair span differently aligned planes due to their viewing directions and their connecting line.

[0061] Fig. 6 shows results of the simulations in a diagram of the resulting measurement error as a function of the extent of the respective error, measured in pixels, in particular fractions of pixels.

[0062] Distance errors AF only influence the resulting root mean square measurement error to a small extent.

[0063] The measurement error is therefore mainly influenced by rotation errors.

[0064] Strabismus angle errors SF have an approximately linear effect.

[0065] Surprisingly, however, it has been shown that tilt angle errors (NF) only slightly influence the measurement error up to a certain extent. However, if the tilt angle errors (NF) exceed a threshold, the measurement error increases disproportionately.

[0066] The simulations revealed a tilt angle error threshold of approximately 0.3 pixels, above which tilt angle errors (NF) had a significant impact. For example, increasing the tilt angle error (NF) from 0.3 pixels to 0.5 pixels resulted in a sixfold increase in the error, i.e., the cumulative drift.

[0067] For a field of view with a viewing angle of 90° for a camera that is vertically mapped to 1536 pixels, for example, an error of 0.3 pixels corresponds to an angular error of

[0068] 0.3 pixels x 90° / 1536 pixels = approx. 0.018°.

[0069] One of the reasons for this may be that the applied SLAM methods are only capable of successfully assigning at least some of the elements contained in the images from the various cameras 16, 18, 20, 22, 24, 26 to one another up to the aforementioned tilt angle error threshold. A particularly advantageous position measuring device 10 can therefore be characterized in that a tilt angle error NF between cameras 16, 18, 20, 22, 24, 26 of at least one of the camera pairs is at most 0.3 pixels.

[0070] The position measuring device 10 can be configured to automatically measure, correct, and / or calculate an inclination angle error NF between at least one of the camera pairs. In particular, the inclination angle error NF can be limited to a maximum of 0.3 pixels. This can be achieved, for example, by the position measuring device 10, in particular the controller 32, being configured to calibrate the respective camera pair, in particular all camera pairs.

[0071] Calibration can be performed by recording images of known content by the respective cameras 16, 18, 20, 22, 24, 26 of the respective camera pair. In a dimension in which the two cameras of the camera pair should not be offset or rotated relative to one another, the recorded images should contain identically positioned elements. For example, if images of a point are recorded and the two cameras are offset horizontally but not vertically, and if the cameras are aligned identically vertically, the recorded element should be depicted at the same vertical position within the recorded image. A corresponding vertical offset can then be calculated out in subsequently recorded images. Alternatively or additionally, the cameras can be adjustably mounted on the holder 28. For example, they can be arranged on the holder 28 so that they can be adjusted by a motor.A mechanical correction can then also be performed, so that during subsequent calibration, only a minor or, ideally, no offset can be detected. It goes without saying that such a correction method can also be applied to dimensions other than the vertical dimension mentioned here as an example, in particular to a horizontal dimension perpendicular to it.

[0072] It is also conceivable to carry out such a calibration, in particular a computational compensation and / or, if the required mechanical components are available, a mechanical correction, repeatedly.

[0073] For example, if the position of a position marker is measured, where the appearance of the position marker, in particular, for example, the dimensions of the position marker, are precisely known, images of the position marker can be used for calibration analogously to the procedure in the aforementioned example. For this purpose, the position markers 102 provided as calibration markers can be used, for example. If the appearance of the respective position markers is known, other position markers can also be used instead of or in addition to the position markers 102.

[0074] It is therefore conceivable that the position measuring device 10 is set up to correct and / or calculate out a distance error AF, a squint angle error SF and / or an inclination angle error NF with the aid of image recordings from at least two of the cameras 16, 18, 20, 22, 24, 26, in particular a pair of cameras, of at least two objects whose position and preferably also their appearance is known, for example at least two of the position markings 102 used as calibration markings.

[0075] For this purpose, the position measuring device 10 can be configured to identify the position marking 102 in at least one image recording of one of the cameras 16, 18, 20, 22, 24, 26, in particular in several image recordings of different cameras 16, 18, 20, 22, 24, 26.

[0076] Fig. 7 shows a position measuring system 100 on a building construction site 14 with a floor 104 and a wall 106. The position measuring system 100 comprises a position measuring device 10 and a dipstick 108, which is guided or at least guideable by a user 106. The position measuring device 10 can, unless otherwise described below, correspond to one of the previously described position measuring devices 10.

[0077] The position and location of the dipstick 108, in particular its tip 109, and thus the position P contacted by the tip 109, can be measured by the position measuring system 100.

[0078] For this purpose, the dipstick 108 has three position markings 110, 112, and 114. The position markings 110, 112, and 114 each protrude from a central rod 116 of the dipstick 108. The rod 116 and the position markings 110, 112, and 114 can be made of a low-thermal-expansion material, for example, a so-called "INVAR" steel.

[0079] The relative positions of the position markings 110, 112, and 114 to each other, as well as to the rod 116 and the tip 109, are known. The position markings 110, 112, and 114 together span a volume and thus form a three-dimensional position marking 115. From the positions of the position markings 110, 112, and 114, the position of the tip 109 and thus the position P can be clearly determined, even if the dipstick 108 is not exactly vertically aligned.

[0080] The position measuring device 10 is configured to record the position markings 102 and 110, 112 and 114 with the aid of its six cameras 16, 18, 20, 22, 24, 26, in particular those of the cameras 16, 18, 20, 22, 24, 26, whose field of view captures the respective position markings 110, 112, 114, and to evaluate the corresponding images in order to determine the position P therefrom, for example photogrammetrically.

[0081] In particular, the cameras 16, 18, 20, 22, 24, 26 of the position measuring device 10 can record images of the position markings 110, 112, and 114. From the stereoscopic or multiscopic images, the position measuring device 10, in particular its controller 32, can identify position markings 110, 112, and 114 in the recorded images and localize them at the respective image positions in the images. From the identified image positions, the positions of the position markings 110, 112, 114 can be determined. From these positions and taking into account the geometry of the rod 116, in particular the relative position of the tip 109, the position measuring device 10 can then calculate the position of the tip 109 and thus the position of position P.

[0082] To increase accuracy, the position measuring device 10 can have a distance meter 118. The distance meter 118 can comprise a laser. In particular, it can be arranged on the position measuring device 10 in an adjustable manner, preferably by motor, so that it can, for example, target and, if necessary, track a target 120 located on the rod 116, for example a prism. A distance dx of the distance meter 118 to the target 120 measured by the distance meter 118 can additionally be used to determine the position of point P. The position determinations can be made, in particular, with reference to a body-specific coordinate system of the position measuring device 10.

[0083] In order to reference the position P in the independent coordinate system K and thus compare it, for example, with a BIM model, several position markers 102 are arranged on the floor 104 and the wall 106 on the construction site 14. They are all located within the field of view of the cameras of the position measuring device 10. They have been pre-measured and have known coordinates relative to the coordinate system K. The position markers 102 can thus in turn serve as calibration markers.

[0084] To map the body's own coordinate system in the coordinate system K, images of the position markings 102 can be taken as described above, and the transformation data required for the mapping can be determined photogrammetrically from these, so that the position P is determined in coordinates of the coordinate system K. The accuracy can also be increased here by measuring the respective distances of the distance meter 118 to the position markings 102 with the aid of the distance meter 118 and taking these into account when calculating the transformation data.

[0085] In a further embodiment, one or more of the position markers 110, 112, 114, and / or 102 can also be designed as active position markers. In particular, they can automatically emit light signals. The light signals can be coded. For example, the light signals can be pulsed at one or more specific frequencies.

[0086] The cameras 16, 18, 20, 22, 24, 26 of the position measuring device 10 can take series of images.

[0087] From the image series, the light points generated by the active position markers can be filtered based on their coding, particularly to improve the signal-to-noise ratio and reduce image noise. The filtered images can then be used to determine position P.

[0088] In a further embodiment, it can be provided to calibrate, in particular to measure, correct and / or calculate out at least one inclination angle error of at least one camera pair with the aid of one or more of the position markings 102, 110, 112, 114 and preferably also the respective distances to the respective position markings.

[0089] For example, in the case of active position markers 102, calibration can be performed with knowledge of the actual relative positions and locations of the position markers 102, by comparing these actual relative positions and locations with the relative positions and locations measured from the recorded images and additionally by comparing them with the distances directly measured by the distance meter 118. If the cameras of the camera pair to be calibrated are motor-adjustable, they can be adjusted, for example, about their axis y (see Fig. 5) until deviations in the relative positions and locations from one another and from the directly measured distances are reduced to a minimum. Analogously, calibration can also be performed based on the known geometry of the three-dimensional position marker 115 and its relative position and location to the target 120, as well as the distance dx.

[0090] Instead of or in addition to a mechanical adjustment of cameras, the images recorded by the cameras can also be mathematically shifted and / or distorted according to a correction image until a mathematical correction image is determined in which the deviations are also reduced to a minimum.

[0091] Such a calibration can be performed repeatedly. For example, the calibration can be performed continuously, e.g., with each determination of position P, i.e., with each determination of the positions of the position markers 110, 112, 114.

[0092] In particular, at least one image error can be measured and / or eliminated. It is particularly preferred if an inclination angle error between cameras of at least one of the camera pairs is determined, corrected, and / or eliminated.

[0093] Fig. 8 shows a flowchart of a method 1000 that also solves the problem.

[0094] To facilitate understanding, method 1000 is explained below using the reference numerals introduced above. As an example, a situation comparable to that shown in Figure 1 is used in which method 1000 is executed.

[0095] In particular, the method 1000 is a method for measuring a position P of an object 12 on a construction site 14, for example a building construction site or a civil engineering construction site, with a position measuring system 100 of the type described above.

[0096] In a phase 1010, images are recorded by the position measuring device 10 using its six cameras 16, 18, 20, 22, 24, 26 with a total of at least 18 MP, wherein at least two of the recorded images contain the position P to be determined and at least two other or the same images contain at least one of the position markings 102 serving as calibration markings, in particular all position markings 102. If necessary, the position measuring device 10 is suitably positioned on the construction site 14 for this purpose. In a phase 1020, i.e., before the actual measurement of the position (P), at least one inclination angle error NF is first measured using images from cameras of a camera pair, which, for example, capture one of the position markings 102 designed as calibration markings and / or another, clearly identifiable image position within the field of view of the camera pair.In subsequent image processing steps, the inclination angle error determined in pixels or fractions of pixels is then automatically corrected and / or calculated out. In particular, it is limited to a maximum of 0.3 pixels by these measures. The inclination angle error NF can, for example, be subsequently calculated out by mathematically offsetting the images from one another according to the degree of the inclination angle error NF. Alternatively or additionally, it can be provided that at least one of the cameras 16, 18, 20, 22, 24 or 26 of a camera pair is arranged so as to be rotatable, in particular motor-rotatable, about the axis x. Thus, one possibility for automatically compensating for the inclination angle error NF is that the rotatably arranged camera 16, 18, 20, 22, 24, 26 or 26 is rotated around the axis x in accordance with the determined inclination angle error NF in order to compensate for the inclination angle error NF.

[0097] In a phase 1030, a sharpness level is determined for each of the images to be evaluated. If the sharpness level falls below a certain sharpness threshold, the corresponding image is acquired again. After a certain number of failed attempts, i.e., if the sharpness threshold is not reached despite repetitions, the method 1000 is aborted with an error message. Instead of or in addition to determining the sharpness, vibrations of the position measuring device 10 can also be detected and compared with a vibration threshold in an analogous manner. If necessary, image acquisitions can be repeated, or the method 1000 can be aborted with an error message after several unsuccessful repetitions.

[0098] Using the images now available, in a phase 1040, the position of at least one position of one of the position markers (102) defined as a calibration marker with respect to a coordinate system (K) is determined, for example, photogrammetrically and / or using a SLAM algorithm, taking into account the geometries of the position-measuring device 10, in particular the relative positions and orientations of the cameras 16, 18, 20, 22, 24, 26. Subsequently, the position P is determined analogously from the available images.

[0099] Based on the positions in the coordinate system K of the position markers 102 and their positions in the images, the position P is converted into coordinates of the coordinate system K.

[0100] Further variants of the method 1000 result from taking into account one or more of the design options as described in connection with the preceding Figs. 1 to 7.

[0101] Further features and advantages of the invention will become apparent from the preceding description of exemplary embodiments of the invention, from the figures of the drawing, which show details essential to the invention, and from the claims. The features shown in the drawing are not necessarily to scale and are presented in such a way that the special features can be clearly seen. The various features can be implemented individually or in combinations in variants of the invention.

[0102] List of reference symbols

[0103] 10 Position measuring device

[0104] 12 objects

[0105] 14 Construction site

[0106] 16 Camera

[0107] 18 Camera

[0108] 20 Camera

[0109] 22 Camera

[0110] 24 Camera

[0111] 26 Camera

[0112] 28 Bracket

[0113] 30 Tripod

[0114] 32 Control

[0115] 34 storage

[0116] 36 Computer program product

[0117] 38 Gravity direction sensor

[0118] 40 Accelerometer

[0119] 100 Position measuring system

[0120] 102 Position marker

[0121] 104 Floor

[0122] 106 Wall

[0123] 106 users

[0124] 108 dipstick

[0125] 109 lace

[0126] 110 Position marker

[0127] 112 Position marker

[0128] 114 Position marker

[0129] 115 three-dimensional position marking

[0130] 116 Staff

[0131] 118 distance meters

[0132] 120 Target

[0133] 1000 procedures

[0134] 1010 phase

[0135] 1020 Phase 1030 Phase

[0136] 1040 phase

[0137] AF distance error dx distance K coordinate system

[0138] NF tilt angle error

[0139] P Position

[0140] SF strabismus

[0141] SNR Image noise TS Exposure times x x-axis y y-axis

Claims

Patent claims 1 . Position measuring device (10) for measuring a position (P) of an object (12) on a construction site (14), for example a building construction site or a civil engineering construction site, comprising at least one camera (16, 18, 20, 22, 24, 26), characterized in that the position measuring device (10) has at least one camera pair consisting of at least two cameras (16, 18, 20, 22, 24, 26), and wherein it is designed to automatically correct and / or calculate out an inclination angle error (NF) between cameras (16, 18, 20, 22, 24, 26) of at least one camera pair, in particular to limit it to a maximum of 0.3 pixels.

2. Position measuring device (10) according to the preceding claim, characterized in that at least one of the cameras (16, 18, 20, 22, 24, 26) is arranged rotated by 90° to at least one other of the cameras (16, 18, 20, 22, 24, 26).

3. Position measuring device (10) according to one of the preceding claims, characterized in that at least two of the cameras (16, 18, 20, 22, 24, 26) in a camera pair are oriented forward, two of the cameras (16, 18, 20, 22, 24, 26) in a camera pair are oriented to the right and two of the cameras (16, 18, 20, 22, 24, 26) in a camera pair are oriented to the left.

4. Position measuring device (10) according to one of the preceding claims, characterized in that an inclination angle error (NF) between cameras (16, 18, 20, 22, 24, 26) of at least one of the camera pairs is at most 0.3 pixels.

5. Position measuring device (10) according to one of the preceding claims, characterized in that the position measuring device (10) has at least six cameras (16, 18, 20, 22, 24, 26) spaced apart from one another, wherein the cameras (16, 18, 20, 22, 24, 26) have a total of at least 18 MP, wherein the position measuring device (10) is set up to determine the position (P) of the object (12) by evaluating images from the at least six cameras (16, 18, 20, 22, 24, 26).

6. Position measuring device (10) according to one of the preceding claims, characterized in that the position measuring device (10) has an inclination sensor, for example a spirit level and / or a gravity direction sensor (38).

7. Position measuring device (10) according to one of the preceding claims, characterized in that the position measuring device (10) has a motion sensor and / or a vibration sensor.

8. Position measuring system (100), comprising a position measuring device (10) according to one of the preceding claims and a dipstick (108) on which a position marking (102) is arranged and / or formed.

9. Method (1000) for measuring a position (P) of an object (12) on a construction site (14), for example a building construction site or a civil engineering construction site, with a position measuring system (100) according to one of the preceding claims, wherein an inclination angle error (NF) between cameras (16, 18, 20, 22, 24, 26) of at least one camera pair is automatically corrected and / or calculated out, in particular is limited to a maximum of 0.3 pixels.

10. Method according to the preceding claim, characterized in that images from a total of at least six cameras (16, 18, 20, 22, 24, 26) are evaluated, wherein the cameras (16, 18, 20, 22, 24, 26) have a total of at least 18 MP. 11 . Method according to one of the two preceding claims, characterized in that a sharpness or blur, in particular a motion-related blur, is determined in at least one image of the cameras (16, 18, 20, 22, 24, 26), and depending on the sharpness or blur - the image is used to measure the position (P) of the object (12), - the image is not used in measuring the position (P) of the object (12), in particular if the sharpness reaches or falls below a threshold or the blur reaches or exceeds a threshold, and / or - the sharpness of the image is corrected before further use.

12. Method according to one of claims 9 to 12, characterized in that it is detected whether the position measuring device (10) and / or the position marking (102) vibrate and / or move, in particular beyond a vibration threshold value.

13. Method according to one of claims 9 to 13, characterized in that in addition to determining the position (P), at least one position (P) of a position marking (102) defined as a calibration marking with respect to a coordinate system (K) is determined.

14. A computer program product (36) stored on a storage medium, which is configured to execute the method (1000) according to one of claims 9 to 14 when executed on a controller (32) of a position measuring device (10) according to one of claims 1 to 8.

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