Elliptical pattern generation for scanning instruments

Abstract

The invention provides elliptical pattern generation for a scanning instrument. The invention relates to a mobile scanning instrument mounted on a carrier vehicle and configured to acquire point cloud data representing a target area. A mobile scanning instrument includes a beam deflecting element having a first wedge and a second wedge rotatably mounted about a central axis. The wedge deflects the scanning beam at a first deflection angle and a second deflection angle. And the two deflection angles are different. The scanning instrument is configured to provide a first scanning pattern having a circular shape by rotating the wedge in the same direction, and to provide a second scanning pattern having an elliptical shape by rotating the wedge in the opposite direction.

Description

Technical Field

[0001] The present invention relates to the structure and operation of a mobile scanning instrument configured to acquire point cloud data representing a target area. The mobile scanning instrument is configured to be mounted on a carrier vehicle, particularly an aerial vehicle, and to acquire point clouds while the carrier vehicle is moving at a carrier speed. Background Art

[0002] To capture two-dimensional or three-dimensional information about a target area, particularly an urban or agricultural area, scanning methods are commonly used. Ideally, a uniform, dense point cloud is provided. General scanning instruments utilize a scanning beam (particularly a laser beam) scanning arrangement and determine the distance of object points based on, for example, time-of-flight measurements. The measured distance information is combined with the emission angle of the scanning beam (e.g., represented as azimuth and elevation angles) to generate a point cloud representing the arrangement. The capture of the point cloud is performed during the spatial movement of the scanning instrument. The self-movement of the scanning instrument (respectively, the movement of the mobile carrier) must be acquired and merged with the scanning data. While the applicability of the present invention is not limited to the field of aerial scanning, many aspects of the present invention will be illustrated by examples of aerial scanning. Specific features of other mobile scanning methods, such as vehicle- or rail-based mapping, can be applied accordingly.

[0003] Aerial scanning is typically performed using an instrument whose beam deflection element generates a scanning pattern by means of a rotational, sawtooth or oscillatory beam deflection pattern relative to the central axis of the scanning instrument. The central axis is typically aligned with the Nadir ("straight down") direction, while the rotational or oscillatory movement provides a periodic scanning pattern.

[0004] The scanning instrument generates scanning pulses in a periodic manner and transmits them according to the scanning pattern. For aerial scanning, the periodic manner is understood in a broad sense, i.e., the generation of the pulses may involve periodic or pseudo-random modulation, or even a combination of both, as disclosed, for example, in EP4148458 A1. Since the pulse generation is provided by pure electronic components, the practical limit of the pulse rate is set by the detection and assignment of the returned pulses. This practical limit is typically the resolution of the aerial multi-pulse (MPiA) ambiguity. Contemporary MPiA resolution methods (e.g., US10,732,282 B2; EP3640670 A1) allow MHz pulse rates at typical flight altitudes.

[0005] Depending on the survey task, different scan pattern parameters or different types of scan patterns are optimal. For example, for surveying urban areas, a scan pattern configured to provide information about vertical walls is desirable. Additionally, due to the shadows cast by buildings, the advantages of a large scan swathwidth cannot be fully utilized. Despite the disadvantages of uniformity, a circular scan pattern, which typically has a relatively small field of view / angle of view, is usually selected for such survey tasks. Throughout this specification, the field of view is defined as having an angular dimension, and the corresponding linear quantity will be referred to as the scan swathwidth. Unless otherwise provided for a circular scan pattern, the field of view and the angle of view will be used interchangeably.

[0006] For example, landscape surveys for agricultural purposes present different conditions. Here, it is desirable to optimize the survey work by performing a wide field of view scan (preferably from a greater flying height). In other words, the scan is performed with the maximum reasonable scan swathwidth. The scan pattern is typically linear or similar.

[0007] It is desirable to provide a flexible system that can perform two types of survey tasks to increase the utilization rate of the survey instrument. Summary of the Invention

[0008] In view of the above, an object of the present invention is to provide greater flexibility when designing survey operations by a mobile scanning instrument.

[0009] A specific object is to provide an adaptable scan pattern for the survey instrument.

[0010] The present invention relates to a mobile scanning instrument configured to be mounted on a carrier vehicle and configured to acquire point cloud data representing a target area.

[0011] The mobile scanning instrument includes a beam deflection element. The beam deflection element includes a central axis, in particular a central axis corresponding to a part of the beam path. Although other arrangements are possible, the central axis typically corresponds to the beam path of the beam entering the beam deflection element and / or to the imaginary beam path of the undeflected outgoing beam.

[0012] The beam deflection element includes a first wedge and a second wedge. The first wedge is rotatably mounted about a central axis and has optical properties for deflecting a scanning beam by a first deflection angle. The second wedge is rotatably mounted about the central axis and has optical properties for deflecting the scanning beam by a second deflection angle. Those skilled in the art understand that the deflection angles include orientation information, i.e., they correspond to vectors rather than scalars. The first wedge and the second wedge are configured to deflect at least the outgoing scanning beam (in particular both the outgoing scanning beam and a part of the reflected scanning beam). In other words, the outgoing scanning beam is deflected by both the first wedge and the second wedge. As an example, the first wedge is understood to be the first wedge in the direction of the outgoing scanning beam. Furthermore, from here on, it is assumed that the scanning instrument is using a monochromatic scanning beam, in particular a laser beam, and the optical properties of the different components are defined with respect to the wavelength of the scanning beam. The specific properties of other types of scanning instruments can be applied accordingly.

[0013] Those skilled in the art understand that due to fundamental physical principles, the deflection angles correspond to specific angular ranges of the wedges relative to the scanning beam. Furthermore, the deflection angles represent approximate models, and when designing complex optical systems, the skilled person can use different, more accurate models. Although some embodiments of the claimed invention include components shaped as frustum solids (in particular frustum cylinders) with non-parallel bases as one of the first and second wedges, the wedge should be understood as a component that provides beam deflection with a given beam deflection angle, regardless of its form or whether it is an integral component or includes sub-components. For example, from here on, it is assumed that the wedge is embodied as a refractive beam deflection element. The specific properties of other beam deflection elements (in particular refractive elements) can be applied accordingly.

[0014] For the scanning instrument according to the invention, the first wedge and the second wedge are constructed such that the second deflection angle is different from the first deflection angle. In other words, the first wedge and the second wedge are equivalent to (in particular embodied as) a generalized Risley prism pair.

[0015] The scanning instrument is configured to set the first wedge to rotate at a first rate in a first direction and the second wedge to rotate at a second rate in a second direction. It is obvious to those skilled in the art that the scanning instrument of the invention is configured to perform the acquisition of a point cloud such that the two wedges rotate and deflect the scanning beam according to their respective parameters. In particular, the first rate and the second rate are adjustable, specifically such that the second rate has a defined relationship with the first rate, in particular such that the two remain equal.

[0016] The scanning instrument is configured to provide a first scanning pattern having a circular shape with respect to a central axis by setting a second direction equal to a first direction. The circular shape in the sense of the present invention should be understood in a broader sense. In particular, a rose curve or a pattern with a slowly varying mean diameter with respect to a first rate is also considered to be a pattern having a circular shape.

[0017] The scanning instrument is configured to provide a second scanning pattern having an elliptical shape with respect to a central axis by setting a second direction opposite to the first direction. The considerations regarding the first scanning pattern apply correspondingly to the second scanning pattern.

[0018] In some embodiments, the scanning instrument is configured to provide the first and second scanning patterns by setting a second rate equal to the first rate. In particular, equal means equal enough to achieve a first pattern with a stable viewing angle and / or a second scanning pattern with a stable orientation, especially a yaw angle, with respect to the reference frame of the scanning instrument. Setting the rate can be performed manually, e.g., via a potentiometer-based interaction element, semi-automatically based on an operator command, e.g., via a hardware that presses a software button or activates a check box, or fully automatically as a hard-coded feature.

[0019] In some embodiments, the first wedge is embodied as a cylindrical wedge presenting a first wedge angle. The first wedge is made of a transparent material, in particular flint glass, having a refractive index in the range of 1.7 to 2.3. Applying a transparent material with a high refractive index allows for a compact design with a large deflection angle. A person skilled in the art can further determine the corresponding geometric and material properties considering, for example, weight and / or size constraints.

[0020] The second wedge is embodied as a cylindrical wedge presenting a second wedge angle. The second wedge is made of a transparent material, in particular flint glass, having a refractive index in the range of 1.7 to 2.3. For such an embodiment, a deflection angle is provided based on the corresponding wedge angles and refractive indices.

[0021] In some specific embodiments, the second refractive index is equal to the first refractive index, in other words, the two wedges are formed of the same material or materials having similar refractive indices. Such an embodiment can advantageously be combined with an embodiment in which the plane of the wedge closer to the other wedge is perpendicular to the central axis, i.e., where the air gap between the wedges only causes a negligibly small parallel displacement of the scanning beam. To ensure different first and second deflection angles, the first and second wedge angles are designed to be unequal.

[0022] In some embodiments, the first wedge is mounted such that the plane closer to the second wedge is perpendicular to the central axis. The second wedge is mounted such that the plane closer to the first wedge is perpendicular to the central axis. For example, starting from here, only these embodiments will be discussed in detail, and the specific features of other embodiments can be applied accordingly.

[0023] In some embodiments, the first wedge and the second wedge are configured such that the difference between the first deflection angle and the second deflection angle falls within the range of 2° to 15°. In some specific embodiments, the first deflection angle is less than 15°, and the second deflection angle is greater than 15°.

[0024] In some embodiments, the scanning instrument is configured to be mounted as a payload on an aircraft. In some specific embodiments, the aircraft is one of the following: (i) a helicopter, (ii) a light fixed-wing aircraft with a gross takeoff weight of less than 6000 kg, and (iii) a large UAV with a weight exceeding 150 kg. In other words, some embodiments of the scanning instrument of the present invention have a relatively large weight and / or spatial extent and are envisioned for professional surveying purposes. The mobile scanning instrument can be configured to be mounted such that the central axis corresponds to the direction of the lowest point. Alternatively, the mounting of the scanning instrument can provide adjustment options for the central axis.

[0025] In some specific embodiments, the scanning instrument is configured to provide compensation for roll and / or pitch of the aircraft. In particular, the scanning instrument includes a third wedge mounted in the beam path in an adjustable manner to compensate for roll and / or pitch. It is envisioned that the third wedge provides a limited adjustment range and / or slow movement, for example similar to the embodiments disclosed in EP3825722 B1.

[0026] Alternatively or additionally, the scanning instrument can include a fourth wedge, which is particularly mounted in a fixed spatial relationship with the first wedge and is configured to provide a beam deflection with a fourth wedge angle to the outgoing measurement beam to compensate for the angular difference between the outgoing measurement beam and the returned radiation due to the limited round-trip time of the emitted measurement beam. The fourth wedge can be mounted in the beam path along the central axis at a position before the first wedge (i.e., closer to the source than the first wedge).

[0027] In some embodiments, the mobile scanning instrument is configured to set the viewing angle of the first scanning pattern around the central axis. In other words, the embodiment is configured to provide a settable scanning radius for the circular pattern. The setting of the viewing angle is performed by setting the first phase shift and by setting the first wedge and the second wedge to rotate with a phase difference corresponding to the first phase shift. In some specific embodiments, the mobile scanning instrument is configured to set the viewing angle to be less than 40°. The mobile scanning instrument may also be configured to set the viewing angle to be greater than 50°.

[0028] In some embodiments, the mobile scanning instrument is configured to set the displacement angle of the second scanning pattern. The displacement angle represents a rotation around the central axis. In other words, the scanning instrument is configured to provide different alignments of the major axis of the elliptical scanning pattern, particularly different alignments relative to the flight direction. The displacement of the second scanning pattern is performed by setting the second phase shift and by setting the first wedge and the second wedge to rotate with a phase difference corresponding to the second phase shift. Displacing the second scanning pattern is beneficial because it allows the instrument to provide a wide pattern for landscape surveys of substantially flat terrain or a narrow pattern for surveys of urban environments or valleys.

[0029] In some embodiments, the first rate is at least 50 Hz, particularly greater than 100 Hz. In some specific embodiments, the scanning instrument is configured to provide the scanning beam as a pulsed laser beam, wherein the pulse repetition rate exceeds 1 MHz.

[0030] The invention also relates to a method for controlling a moving scanning instrument having a beam deflection element according to the invention. In other words, the beam deflection element comprises (i) a central axis, in particular a central axis corresponding to a part of the beam path, (ii) a first wedge-shaped member rotatably mounted about the central axis and having optical properties for deflecting a scanning beam by a first deflection angle, and (iii) a second wedge-shaped member rotatably mounted about the central axis and having optical properties for deflecting a scanning beam by a second deflection angle different from the first deflection angle. The method comprises the steps of: (i) selecting a scanning pattern from a set of enabled scanning patterns, (ii) providing rotation parameters based on the selected scanning pattern, and (iii) setting the first wedge-shaped member and the second wedge-shaped member to rotate corresponding to the rotation parameters. The rotation parameters include (a) a first rate and a first direction, the first rate and the first direction defining the rotation of the first wedge-shaped member about the central axis, and (b) a second rate and a second direction, the second rate and the second direction defining the rotation of the second wedge-shaped member about the central axis. It goes without saying for a person skilled in the art that the use of numbers and letters does not represent, for example, the order of performing the steps. These and all other numbers do not represent a temporal and spatial connection, not even in the form of a preferred order, and are only for the purpose of readability.

[0031] The set of enabled scanning patterns includes a first scanning pattern having a circular shape with respect to the central axis. The rotation parameters corresponding to the first scanning pattern are such that the second direction is equal to the first direction. The set of enabled scanning patterns includes a second scanning pattern having an elliptical shape with respect to the central axis. The rotation parameters corresponding to the second scanning pattern are such that the second direction is opposite to the first direction.

[0032] In some embodiments, the method further comprises setting the viewing angle of the first scanning pattern about the central axis by providing a first phase shift and by setting the first wedge-shaped member and the second wedge-shaped member to rotate with a phase difference corresponding to the first phase shift. In other words, the method provides a settable scanning radius for the circular pattern. The viewing angle varies in such a way that in particular at least one settable viewing angle is less than 40° and another settable viewing angle is greater than 50°. In some specific embodiments, the first rate and the second rate are also equal.

[0033] In some embodiments, the method further comprises providing a displacement of the second scanning pattern by a displacement angle representing a rotation about the central axis by providing a second phase shift and setting the first wedge-shaped member and the second wedge-shaped member to rotate with a phase difference corresponding to the second phase shift. In some specific embodiments, the first rate and the second rate are also equal.

[0034] The present invention also relates to a computer program product, the computer program product comprising program code segments stored on a machine-readable medium or embodied by electromagnetic waves, and the program code segments having computer-executable instructions for controlling a mobile scanning instrument having a beam deflection element. The beam deflection element comprises (i) a central axis, in particular a central axis corresponding to a part of the beam path, (ii) a first wedge rotatably mounted about the central axis and having optical properties for deflecting the scanning beam by a first deflection angle, and (iii) a second wedge rotatably mounted about the central axis and having optical properties for deflecting the scanning beam by a second deflection angle different from the first deflection angle. The computer program product comprises computer-executable instructions for performing the following operations: (i) accessing input data comprising a pattern selection command, (ii) selecting a scanning pattern from a database of enabled scanning patterns based on the input data, (iii) providing rotation parameters based on the selected scanning pattern, and (iv) providing output data comprising commands for setting the first wedge and the second wedge to rotate corresponding to the rotation parameters. The rotation parameters comprise (a) a first rate and a first direction, the first rate and the first direction defining the rotation of the first wedge about the central axis, and (b) a second rate and a second direction, the second rate and the second direction defining the rotation of the second wedge about the central axis. The database of enabled scanning patterns comprises a first scanning pattern having a circular shape relative to the central axis. The rotation parameters corresponding to the first scanning pattern cause the second direction to be equal to the first direction. The database of enabled scanning patterns comprises a second scanning pattern having an elliptical shape relative to the central axis. The rotation parameters corresponding to the second scanning pattern cause the second direction to be opposite to the first direction.

[0035] In some embodiments, the computer program product comprises computer-executable instructions for performing the selected embodiments of the method. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] By way of example only, specific embodiments of the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which:

[0037] Figure 1a An aircraft performing a prior art survey of a rural area using a linear scanning pattern is depicted.

[0038] Figure 1b A helicopter performing a prior art survey of an urban area using a circular scanning pattern is depicted.

[0039] Figures 2a to 2c An elliptical pattern having three orientations relative to the central axis is depicted.

[0040] Figure 3Schematic diagram depicting an embodiment of the scanning instrument of the present invention.

[0041] Figure 4 Schematic diagram depicting an embodiment of the first wedge and the second wedge and their corresponding optical properties.

[0042] Figure 5a and Figure 5b Schematic diagram showing the influence of the first phase shift on the first scanning pattern.

[0043] Figure 6a and Figure 6b Schematic diagram showing the influence of the second phase shift on the second scanning pattern.

[0044] Figure 7 The flowchart illustrates the selection of a scanning type with desired scanning parameters. Detailed Description

[0045] Figure 1a Shows a prior art mobile scanning instrument 1 carried by an aircraft 4, which acquires point cloud data from a target area 2 when the aircraft 4 travels at a carrier speed 40 relative to the target area 2. The target area is a wooded hilly area that does not include vertical walls. That is, the scanning task is landscape scanning.

[0046] The mobile scanning instrument 1 is typically mounted together with additional survey elements and cameras facing downward or in an inclined direction. The central axis 10 of the mobile scanning instrument 1 is aligned with the carrier speed 40 in a known manner. In the depicted embodiment, the central axis 10 is aligned with the lowest point. The object distance 21 between the target area 2 and the scanning instrument 1 can be defined relative to the central axis 10, as depicted. Alternative mountings (e.g., the central axis 10 can be inclined relative to the carrier speed 40 and point to one side, forward, or backward) are also within the scope of the present invention. The scanning instrument 1 is configured to provide a scanning pattern 3 depicted as a line pattern. This pattern is well-suited for the depicted landscape scanning because it allows a large field of view 30, i.e., a large scanning bandwidth.

[0047] Figure 1b Shows another typical survey task, where a helicopter, as the carrier vehicle 4, performs urban scanning using a scanning beam 11 while traveling at a carrier speed 40. The target area 2 includes objects having vertical or near-vertical surfaces 231, such as houses 23. In addition, there may be a significant height difference between the top surface 230 of the object 23 and the ground plane 24 represented by the street.

[0048] To obtain information about the vertical plane 231, it is advantageous to provide a first scan pattern 31 having a circular shape. The scanning instrument 1 deflects the beam 11 by rotating the beam 11 along the scan pattern 31. The actual position of the object point is determined by the scan pattern 31 and the carrier speed 40. Object points from the actual cycle 310 are represented by solid circles, while object points from the previous cycle 311 are represented by hollow circles. For example, the depicted object points correspond to the case of equiangular distance, or in other words, a strictly periodic pulse rate.

[0049] Of particular importance are the object point 232 corresponding to the vertical plane 231 and the pair of object points 239, 241 corresponding to the transition from the ground plane 24 to the top surface 230 of the object. Due to the high density of the object 23 and the requirement to obtain data from the vertical plane 231, it is beneficial to perform the scan with a smaller field of view (e.g., 40° or less).

[0050] Figure 1b The target points 310, 311 depicted correspond to a strictly periodic pulse train. This embodiment is chosen for illustrative purposes only, and the present invention is not limited to any particular pulse sequence / pulse train.

[0051] Figures 1a to 1b Two main scan tasks with different requirements are depicted. It is advantageous to have a scanning instrument configured to adjust its scan parameters to perform both types of tasks.

[0052] Figures 2a to 2c The carrier vehicle 4, depicted as a helicopter, is shown traveling at a carrier speed 40 and equipped with a scanning instrument 1 that provides a second scan pattern 32 having an elliptical shape about a central axis 10. The depicted central axis 10 is perpendicular to the carrier speed and corresponds to the lowest point direction. This choice is for purely instructional reasons, and the present invention is not limited to this embodiment. For transparency reasons, the pattern 32 is depicted in a reference frame that moves with the central axis 10. Similar to Figure 1b the case shown, object points are generated. The present invention is not limited to the case of a strictly periodic pulse rate depicted, but a modulated pulse rate can also be applied.

[0053] The elliptical pattern 32 provides some advantageous characteristics of Figure 1a and Figure 1b the line pattern and the circular pattern, respectively. The major axis 326 of the ellipse can cover a large field of view corresponding to the line pattern, e.g., about 60°. Advantageously, the point density approximately doubles due to scanning the same field of view twice. Since the scanning beam is always emitted at an oblique angle, the elliptical pattern enables the scanning of vertical objects.

[0054] Figure 2adepicts an elliptical pattern 32 such that its major axis 326 is perpendicular to the carrier velocity 40. This embodiment is advantageous because it provides the maximum scanning bandwidth. Other embodiments are also possible. In Figure 2b it, the major axis 326 is parallel to the carrier velocity 40, which results in a small scanning bandwidth, yet the result is an increased point density. Figure 2c shows an intermediate case, where the elliptical pattern 32 is shifted by a displacement angle 324. The displacement angle 324 can be set based on the scanning task and can be adjusted specifically according to the carrier velocity and the terrain inclination to achieve the same point density perpendicular and parallel to the carrier velocity.

[0055] Figure 3 schematically depicts a scanning instrument 1 having a transmission unit 5, the transmission unit 5 having a beam deflection element 50 including a first wedge 51 and a second wedge 52. The transmission unit 5 further includes a pulse source 340, a focusing / collimating element 341, and a mirror 342 to direct the beam towards the beam deflection element 50. In the depicted embodiment, a portion of the beam path 34 corresponds to the central axis 10 of the transmission unit 5 or the scanning instrument 1. Other embodiments are also possible, and specific features should be applied accordingly. The beam deflection element 50 defines the actual transmission direction 33 of the scanning pulse, i.e., by providing an actual deflection angle 535 to define the actual transmission direction 33 of the scanning pulse. The actual transmission direction 33 is provided with a periodic change along the scanning pattern by rotating 510, 520 the first wedge 51 and the second wedge 52 with corresponding motors 61, 62.

[0056] The depicted first wedge 51 and second wedge 52 are mounted such that the planes 512, 521 closer to the other wedge are perpendicular to the central axis 10. Alternative mountings, such as where the plane further away from the other wedge is perpendicular to the central axis 10, or where these planes are angled with respect to the central axis 10, are also within the scope of the present invention. From the depicted embodiment, it is also clear to a person skilled in the art that, in the kinematic sense, the central axis 10 is not the forced rotation axis of the wedges 51, 52.

[0057] The wedges 51, 52 are formed of a transparent material, in particular flint glass with a refractive index higher than 1.7. The high refractive index is advantageous because it allows for a large deflection angle for a relatively compact design. For example, the first wedge 51 and the second wedge 52 can be formed of the same material.

[0058] The depicted scanning instrument 1 further includes a detection unit 70 having a sensing element 700 adapted to the focusing optics 701. The detection unit 70 is configured to acquire pulses backscattered from a target area (not shown). The depicted scanning instrument further includes a control unit 6 configured to control the pulse source 340, the motors 61, 62 driving the wedges 51, 52 and access data from the detection unit (not shown).

[0059] Those skilled in the art understand that in the above schematic representation, some of the basic features of the claimed invention may be omitted and / or shown in a simplified manner. In addition, some of the depicted features, although advantageous, may not be strictly necessary for implementing the present invention. These features should not be construed as limiting the claimed subject matter, which is defined solely by the claims.

[0060] Figure 4 The beam deflection effect provided by the first wedge 51 and the second wedge 52 is shown. The wedges 51, 52 are embodied as frustum cylinders or, in other words, cylindrical wedges having respective wedge angles 513, 523. The wedges 51, 52 are arranged as a generalized Risley prism pair. That is, the inner planes 512, 521 closer to the other wedge are parallel to each other and, in particular, perpendicular to the central axis 10, corresponding to a part of the beam path 34 of the incident beam. There is a thin air gap 516 between the two wedges 51, 52 to ensure the independent rotatability of the wedges (not shown).

[0061] The wedges 51, 52 are formed of a transparent material having respective refractive indices n1, n2. As an example, it is assumed that n1 = n2, i.e., the two wedges are made of the same material. The beam path 34 causes the incident beam to be deflected twice at the respective outer planes 511, 522 of the wedges 51, 52. That is, for reasons of transparency, the internal deflection that causes a small parallel offset at the air gap 516 is ignored. The actual beam path 34 does not achieve the first deflection angle 515 and the second deflection angle 525 because they are related to the imaginary beam path 534 that would exist if only one of the wedges 51, 52 were applied.

[0062] Figure 5a and Figure 5b Illustrates the concept of adjusting the viewing angles 300, 301 of the first scan pattern 31 by introducing a first phase shift 319. In Figure 5a In the top row, a first embodiment of the first scan pattern 31 is shown, where the first phase shift between the first deflection angle 515 and the second deflection angle 525 is zero, i.e., they are aligned, and the actual deflection angle 535 has the maximum amplitude. In the bottom row, the phases 517, 527 of the corresponding deflection angles 515, 525 reduced to the ±π interval as a function of time are depicted.

[0063] According to the characteristics of the first scanning pattern 31, the first direction 510 and the second direction 520 (shown in only one panel) are equal. For reasons of transparency, the first rate 519 and the second rate 529 are also depicted as being equal. Since the first phase shift is zero in this embodiment, the first deflection angle 515 and the second deflection angle 525 are in phase. The viewing angle 300 of this first embodiment of the first scanning pattern 31 is the highest.

[0064] A second embodiment of the first scanning pattern 318 is Figure 5b The top row of FIG. 5 shows the phases 517, 527 of the respective deflection angles 515, 525 as a function of time, while the bottom row depicts the phases 517, 527 of the respective deflection angles 515, 525 as a function of time. Here, the first phase shift 319 between the first deflection angle 515 and the second deflection angle 525 makes them perpendicular to each other. Otherwise, Figure 5a and Figure 5b Since the directions 510 , 520 and the velocities are all equal, the actual phase difference 537 between the first deflection angle 515 and the second deflection angle 525 is constant and corresponds to the first phase shift 319 .

[0065] Due to non-zero phase difference 537, i.e. first phase shift 319, the magnitude of actual deflection angle 535 and viewing angle 301 of the second embodiment of first scanning pattern 318 is smaller than the viewing angle of the first embodiment of the first scanning pattern. A minimum viewing angle is provided when first deflection angle 515 and second deflection angle 525 are in opposite states.

[0066] Figure 6a and Figure 6b The concept of adjusting the displacement angle 324 of the second scanning pattern 32, 328 by introducing the second phase shift 329 is illustrated. According to the characteristics of the second scanning pattern 32, the first direction 510 and the second direction 520 are opposite to each other. The first rate 519 and the second rate 529 are depicted as equal, that is, the first deflection angle 515 and the second deflection angle 525 rotate at the same speed but in opposite directions, that is, the corresponding phases 517, 527 change in opposite ways. This means that during one complete rotation, when the actual deflection angle 535 scans the elliptical second scanning pattern 32, 328, the first deflection angle 515 and the second deflection angle 525 experience all actual phase differences 537 from the ±π interval.

[0067] therefore, Figure 6b The second embodiment of the second scanning pattern 328 depicted in Figure 6a The first embodiment of the second pattern 32 depicted in FIG. 3 differs only in the displacement 324 of the major axis 326 relative to the fixed orientation. Alternatively, as represented by the actual phase difference 537, the point 536 where the actual phase difference 537 is zero (or equivalently 2nπ) is shifted due to the introduction of the second phase shift 329.

[0068] Figure 7 The provision of a scan pattern with corresponding scan parameters 821 is schematically depicted by a flow chart. Command / flow lines are shown in bold and data lines are shown as dashed arrows. Those skilled in the art will understand that the depicted flow chart focuses on the features of the claimed invention and that the actual implementation also includes elements not depicted, in particular command or data elements and / or data transmission lines. Additionally, for reasons of clarity and conciseness, command or data modules may be depicted in a simplified form.

[0069] In a first step, a type 82 of scan pattern is selected 820 based on a database of enabled scan patterns 80 and accessing 810 a pattern selection command 81 (in particular from an operator). Scan parameters 821, such as field of view, scan rate, pulse rate, are accessed 822 relative to the selected scan pattern type 82. In particular, if an implementation of a first scan pattern is selected 820, the user interface may enable manual entry of a desired viewing angle, but if an implementation of a second scan pattern is selected 820, that option will be hidden. Based on the selected scan pattern type 82 and the desired scan parameters 821, rotation parameters 83, in particular the orientation and rate of a wedge and a corresponding phase shift, are derived 830. The rotation parameters 83 are then converted 840 into a wedge rotation command 84.

[0070] Although the above part illustrates the present invention with reference to some specific embodiments, it must be understood that many modifications and combinations can be made to the different features of the embodiments. All such modifications are within the scope of the appended claims.

Claims

1. A mobile scanning device (1), the mobile scanning device (1) being configured to be mounted on a carrier vehicle (4) and configured to acquire point cloud data representing a target area (2), wherein: The mobile scanning device (1) comprises a beam deflection element (50), wherein the beam deflection element (50) comprises: a central axis (10), in particular a central axis (10) corresponding to a portion of the beam path (34), a first wedge (51) which is mounted rotatably about the central axis (10) and has optical properties for deflecting the scanning beam (11) at a first deflection angle (515), a second wedge (52) which is mounted rotatably about the central axis (10) and has optical properties for deflecting the scanning beam (11) at a second deflection angle (525), Wherein, the mobile scanning device (1) is configured as follows: - arranging the first wedge (51) to rotate in a first direction (510) at a first rate (519) and arranging the second wedge (52) to rotate in a second direction (520) at a second rate (529), and - providing a first scanning pattern (31, 318) having a circular shape relative to the central axis (10) by setting the second direction (520) equal to the first direction (510), It is characterized in that - the first wedge (51) and the second wedge (52) are constructed such that the second deflection angle (525) is different from the first deflection angle (515), The mobile scanning device (1) is configured to provide a second scanning pattern (32, 328) having an elliptical shape relative to the central axis (10) by arranging the second direction (520) opposite to the first direction (510).

2. The scanning instrument (1) according to claim 1 is configured to provide the first scanning pattern (31, 318) and the second scanning pattern (32, 328) by setting the second rate (529) equal to the first rate (519).

3. The scanning device (1) according to any one of claims 1 to 2, wherein: - the first wedge (51) o is embodied as a cylindrical wedge exhibiting a first wedge angle (513), and o is made of a transparent material having a first refractive index (n1), - The second wedge (52) o is embodied as a cylindrical wedge exhibiting a second wedge angle (523), and o is made of a transparent material having a second refractive index (n2), - providing said deflection angle (515, 525) based on the corresponding wedge angle (513, 523) and the refractive index (n1, n2), In particular, - the first refractive index (n1) falls within the interval of 1.7 to 2.3, The second refractive index (n2) is equal to the first refractive index (n1), and the first wedge angle (513) and the second wedge angle (523) are designed to be unequal.

4. The scanning device (1) according to claim 3, wherein: - the first wedge (51) is mounted so that the plane (512) closer to the second wedge (52) is perpendicular to the central axis (10), - The second wedge (52) is mounted so that the plane (521) closer to the first wedge (51) is perpendicular to the central axis (10).

5. A scanning device (1) according to any one of the preceding claims, wherein: The first wedge (51) and the second wedge (52) are constructed so that the difference between the first deflection angle (515) and the second deflection angle (525) falls within the range of 2° to 15°, in particular, wherein the first deflection angle (515) is less than 15° and the second deflection angle (525) is greater than 15°.

6. The scanning device (1) according to any one of the preceding claims, configured to be mounted on an aircraft as a carrier vehicle (4), In particular, - the mobile scanning device (1) is mounted so that the central axis (10) corresponds to the nadir direction, and - The aircraft is one of the following: o Helicopters, o light fixed-wing aircraft, the gross take-off weight of which is less than 6000kg, o large UAV, the weight of which exceeds 150kg.

7. The scanning device (1) according to claim 6 is configured to provide compensation for the roll and / or pitch of the aircraft, in particular by including a third wedge mounted in the beam path (34) in an adjustably manner to provide compensation for the roll and / or pitch of the aircraft.

8. The mobile scanning device (1) according to any one of the preceding claims, the mobile scanning device (1) being configured to set the viewing angle (300, 301) of the first scanning pattern (31, 318) around the central axis (10) by setting a first phase shift (319) and by setting the first wedge (51) and the second wedge (52) to rotate with a phase difference corresponding to the first phase shift (319), In particular, the mobile scanning device (1) is configured to set the viewing angle (300, 301) to be less than 40°.

9. A mobile scanning device (1) according to any one of the preceding claims, wherein the mobile scanning device (1) is configured to set a displacement angle (324) of the second scanning pattern (32, 328) corresponding to a rotation around the central axis (10) by setting a second phase shift (329) and by setting the first wedge (51) and the second wedge (52) to rotate with a phase difference corresponding to the second phase shift (329).

10. The mobile scanning device (1) according to any one of the preceding claims, wherein: The first rate (519) is at least 50 Hz.

11. A method of controlling a mobile scanning device (1) having a beam deflection element (50), the beam deflection element (50) comprising: a central axis (10), in particular a central axis (10) corresponding to a portion of the beam path (34), a first wedge (51) which is mounted rotatably about the central axis (10) and has optical properties for deflecting the scanning beam (11) at a first deflection angle (515), and a second wedge (52) which is mounted rotatably about the central axis (10) and has optical properties for deflecting the scanning beam (11) at a second deflection angle (525) different from the first deflection angle (515), The method comprises the following steps: - selecting (820) a scanning pattern (3, 31, 32, 318, 328) from a set of enabled scanning patterns (80), - providing (830) rotation parameters (83) based on the selected scanning pattern (82), wherein the rotation parameters (83) include: o a first rate (519) and a first direction (510), the first rate (519) and the first direction (510) defining a rotation of the first wedge (51) about the central axis (10), and o a second rate (529) and a second direction (520), wherein the second rate (529) and the second direction (520) define a rotation of the second wedge (52) about the central axis (10), - setting (840) the first wedge (51) and the second wedge (52) to rotate corresponding to the rotation parameter (83), in, - the set of enabled scanning patterns (80) comprises a first scanning pattern (31, 318) having a circular shape relative to the central axis (10), and - the rotation parameter (83) corresponding to the first scanning pattern (31, 318) is such that the second direction (520) is equal to the first direction (510), It is characterized in that - the set of enabled scanning patterns (80) comprises a second scanning pattern (32, 328) having an elliptical shape relative to the central axis (10), and - the rotation parameter (83) corresponding to the second scanning pattern (32, 328) is such that the second direction (520) is opposite to the first direction (510).

12. The method according to claim 11 further comprises setting the viewing angle (300, 301) of the first scanning pattern (31, 318) around the central axis (10) by providing a first phase shift (319) and by setting the first wedge (51) and the second wedge (52) to rotate with a phase difference corresponding to the first phase shift (319).

13. The method according to claim 11 further includes providing a displacement of the second scanning pattern (32, 328) by a displacement angle (324) corresponding to the rotation around the central axis (10) by providing a second phase shift (329) and by setting the first wedge (51) and the second wedge (52) to rotate with a phase difference corresponding to the second phase shift (329).

14. A computer program product comprising program code segments stored on a machine-readable medium or embodied by electromagnetic waves and having computer-executable instructions for controlling a mobile scanning device (1) having a beam deflection element (50), wherein: The beam deflection element comprises: - a central axis (10), a first wedge (51) which is mounted rotatably about the central axis (10) and has optical properties for deflecting the scanning beam (11) at a first deflection angle (515), and a second wedge (52) which is mounted rotatably about the central axis (10) and has optical properties for deflecting the scanning beam (11) at a second deflection angle (525) different from the first deflection angle (515), The computer program product comprises computer executable instructions for performing: - accessing (810) input data (81) including a pattern selection command, - selecting (820) a scanning pattern (3, 31, 32, 318, 328) from a database of enabled scanning patterns (80) based on the input data (81), - providing (830) rotation parameters (83) based on the selected scanning pattern (82), wherein the rotation parameters (83) include: o a first rate (519) and a first direction (510), wherein the first rate (519) and the first direction (510) define a rotation of the first wedge (51) about the central axis (10), o a second rate (529) and a second direction (520), wherein the second rate (529) and the second direction (520) define a rotation of the second wedge (52) about the central axis (10), - providing (840) output data, wherein the output data includes a command (84) to set the first wedge (51) and the second wedge (52) to rotate corresponding to the rotation parameter (83), in, - the database of enabled scanning patterns (80) comprises a first scanning pattern (31, 318) having a circular shape relative to the central axis (10), and - the rotation parameter (83) corresponding to the first scanning pattern (31, 318) is such that the second direction (520) is equal to the first direction (510), It is characterized in that - the database of enabled scanning patterns (80) comprises a second scanning pattern (32, 328) having an elliptical shape relative to the central axis (10), and - the rotation parameter (83) corresponding to the second scanning pattern (32, 328) is such that the second direction (520) is opposite to the first direction (510).

15. The computer program product of claim 14, wherein: The computer program product comprises computer executable instructions for performing the method according to any one of claims 11 to 13.

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