Laser scanner

Abstract

The disclosed subject matter relates to a laser scanner for scanning a ground from a seaborne or airborne vehicle, comprising a scanning unit for emitting a fan-shaped scan pattern made of laser beams fanned out about a scan axis and for receiving the laser beams reflected off the ground and an evaluation unit connected to the scanning unit for evaluating the laser beams that are received. The laser scanner is characterized by a measuring unit that is designed to measure the height of the vehicle above ground, and an actuation device that can be anchored to the vehicle and that is connected to the measuring unit. The actuation device is designed to rotate the fan-shaped scan pattern of the scanning unit with respect to the vehicle about a first actuation axis that is different from the scan axis, depending on the measured height above the ground.

Claims

1. A laser scanner for scanning a ground from a seaborne or airborne vehicle, comprising a scanning unit configured for emitting a fan-shaped scan pattern made of laser beams fanned out over a fan angle about a scan axis to scan the ground beneath the vehicle in a scanning strip running along a path of the vehicle, and for receiving the laser beams reflected off the ground, an evaluation unit connected to the scanning unit and configured for evaluating the laser beams that are received, a measuring unit configured to measure the height of the vehicle above the ground, and an actuation device connected to the measuring unit and configured to be anchored to the vehicle, wherein the actuation device is configured to rotate the fan-shaped scan pattern of the scanning unit with respect to the vehicle about a first actuation axis by a first actuation angle without changing the fan angle, and wherein the first actuation axis is different from the scan axis and stationary in relation to the vehicle when the actuation device is anchored to the vehicle, and which first actuation angle depends on the measured height above the ground so that a strip width of the scanning strip remains substantially constant during scanning.

2. The laser scanner according to claim 1, wherein the first actuation axis is essentially vertical.

3. The laser scanner according to claim 1, wherein the first actuation axis intersects the scan axis at an origin of the fan-shaped scan pattern.

4. The laser scanner according to claim 1, wherein the measuring unit is configured to measure the height of the vehicle above ground by measuring the time-of-flight of an emitted measurement beam that has been reflected off the ground and received.

5. The laser scanner according to claim 4, wherein the measurement beam is a radar, laser, or sonar measurement beam.

6. The laser scanner according to claim 4, wherein the measurement beam is one of the laser beams that is emitted by the scanning unit and reflected off the ground and received.

7. The laser scanner according to claim 1, wherein the measuring unit has a satellite navigation receiver to measure the three-dimensional position, and wherein the measuring unit is configured to use the position measured by this satellite navigation receiver and a stored terrain model of the ground beneath the vehicle to measure the height of the vehicle above the ground.

8. The laser scanner according to claim 7, wherein said terrain model of the ground is predefined and stored in a memory of the laser scanner.

9. The laser scanner according to claim 7, wherein the evaluation unit is configured to use the direction and time-of-flight of the received laser beams to calculate said terrain model of the ground and to store it in a memory to which the measuring unit has access.

10. The laser scanner according to claim 7, wherein the actuation device is further configured to use the terrain model to determine a slope of the ground beneath the measured position and transverse to a direction of motion of the vehicle and to rotate the fan-shaped scan pattern of the scanning unit with respect to the vehicle about a second actuation axis that is different from the first one and that lies essentially in the direction of motion, depending on the slope that is determined.

11. The laser scanner according to claim 1, further comprising an inertial measurement unit for determining at least one of the values pitch angle, roll angle, and yaw angle, the actuation device being connected to the inertial measurement unit and configured to rotate the fan-shaped scan pattern also to compensate for the determined pitch, roll, and/or yaw angle/s.

12. The laser scanner according to claim 1, wherein the actuation device is configured to rotate the fan-shaped scan pattern of the scanning unit by adjusting a deflection mirror of the scanning unit with respect to the vehicle.

13. The laser scanner according to claim 1, wherein the actuation device is configured to rotate the entire scanning unit with respect to the vehicle.

14. The laser scanner according to claim 1, wherein the actuation device comprises a controller and an actuator controlled by the controller to rotate the fan-shaped scan pattern of the scanning unit with respect to the vehicle.

15. The laser scanner according to claim 14, wherein the controller is part of the evaluation unit.

16. The laser scanner according to claim 6, wherein said one of the laser beams that is emitted by the scanning unit and reflected off the ground and received is a vertically emitted laser beam.

17. A laser scanner for scanning a ground from a seaborne or airborne vehicle, comprising a scanner which emits a fan-shaped scan pattern made of laser beams fanned out over a fan angle about a scan axis to scan the ground beneath the vehicle in a scanning strip running along a path of the vehicle, and for receiving the laser beams reflected off the ground, an evaluator connected to the scanner which evaluates the laser beams that are received, means for measuring the height of the vehicle above the ground, and an actuator controlled by a controller, the actuator being anchored to the vehicle, the controller connected to the measuring means to receive the measured height of the vehicle above the ground, wherein the actuator rotates the fan-shaped scan pattern of the scanner with respect to the vehicle about a first actuation axis by a first actuation angle without changing the fan angle, and wherein the first actuation axis is different from the scan axis and stationary in relation to the vehicle due to the actuator being anchored to the vehicle, and which first actuation angle depends on the measured height above the ground so that a strip width of the scanning strip remains substantially constant during scanning.

18. The laser scanner according the claim 17, wherein the means for measuring the height of the vehicle above the ground includes emitting a measurement beam and measuring the time-of-flight of the measurement beam that has been reflected off the ground and received.

19. The laser scanner according to claim 17, wherein the means for measuring the height of the vehicle above the ground includes a satellite navigation receiver which measures a three-dimensional position, and wherein the three-dimensional position and a terrain model of the ground beneath the vehicle stored in a memory of the laser scanner are used to measure the height of the vehicle above the ground.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosed subject matter is explained in detail below on the basis of sample embodiments that are illustrated in the attached drawings. The drawings are as follows:

(2) FIG. 1 is a perspective view of an airplane with a laser scanner according to the prior art that is scanning the ground;

(3) FIG. 2 is a block diagram of a laser scanner according to this disclosed subject matter;

(4) FIG. 3 is a perspective view of an airplane with the laser scanner according to FIG. 2 that is scanning the ground according to FIG. 1;

(5) FIG. 4a through 4c show the laser scanner of FIG. 2 while scanning according to FIG. 3, shown in a side view (FIG. 4a), a rear view (FIG. 4b), and a top view (FIG. 4c); and

(6) FIGS. 5a and 5b show the laser scanner of FIG. 2 while scanning a ground with a slope transverse to the direction of flight, without slope compensation (FIG. 5a) and with slope compensation (FIG. 5b), each in a front view.

DETAILED DESCRIPTION

(7) According to FIG. 1, a seaborne or airborne vehicle 1, here a manned airplane 1, carries a downward directed laser scanner 3 to scan a ground 2. To accomplish this, the laser scanner 3 produces, e.g., in a single laser source, pulsed or modulated laser beams 4, which an oscillating or rotating optical system, e.g., a continuously rotating polygon mirror wheel, fans out about a scan axis 5 into a fan-shaped scan pattern 6 having a fan angle φ. Alternatively, the laser scanner 3 can have multiple laser sources, which in their totality form the fan-shaped scan pattern 6 by suitable alignment about the scan axis 5. Thus, the fan angle φ is predefined by the structure of the laser scanner 3, and has approximately the shape of a sector of a circle or of a sector of a lateral surface of a cone.

(8) Scanning involves the laser scanner 3 emitting the laser beams 4 onto the overflown ground 2 and receiving the laser beams 4 reflected off the ground 2. To accomplish this, the ground 2 beneath the vehicle 1 is sampled (“scanned”) line by line in a scanning strip 7 having the width w with the lines 8 being separated from one another by a distance d. Every line 8 represents the impingement of the laser beams 4 of a fan-shaped scan pattern 6 onto the ground 2; the emission direction and time-of-flight of the laser beams 4 of the multiple lines 8 are used to calculate a three-dimensional terrain model of the ground 2.

(9) The distance d of the lines 8 results as a consequence of the travel of the airplane 1 and the scanning speed; the strip width w depends on the fan angle φ and on the height of the airplane 1 above the ground 2 (“above ground level”, AGL).

(10) Thus, if the ground 2 comprises a mountain 9, as in the example shown in FIG. 1, the change in strip width w as the mountain 9 is overflown—see, for example, the smaller strip width w.sub.1 on the mountain 9 in comparison with the strip width w in the valley—must, according to the prior art, be compensated for, e.g., by suitable selection of the flight path or multiple overflights, to prevent gaps between adjacent scanning strips 7 during scanning. This results in overlaps of adjacent or crossing scanning strips 7 and, consequently, abrupt changes in the scanning resolution at the borders of the overlap areas and an uneven distribution of the scanning resolution over the ground 2.

(11) On the basis of the examples shown in FIG. 2 through 5, the discussion below describes various embodiments of an inventive laser scanner 10 that allows uniform scanning of the ground 2. The same reference numbers are used to designate the same parts as in FIG. 1.

(12) According to FIG. 2, the laser scanner 10 comprises a scanning unit 11, which—comparable with the laser scanner 3 according to FIG. 1—emits the fan-shaped scan pattern 6 of laser beams 4 fanned-out about the scan axis 5 and receives the laser beams 4 reflected off the ground 2. The received laser beams 4 are evaluated by an evaluation unit 12 that is connected to the scanning unit 11. To accomplish this in the simplest case, the evaluation unit 12 takes the emission direction and time-of-flight of the laser beams 4 and also position values x/y/z, which are produced, for example, by a satellite navigation receiver 13 of the laser scanner 10, and, if necessary, the pitch angle p, the roll angle r, and the yaw angle y of the vehicle 1 from an inertial measurement unit (IMU) 14 of the laser scanner 10, and records all of these in a connected memory 15. The memory 15 can be read out, and the recorded values can be used to calculate a three-dimensional terrain model 3D after the scanning, i.e., “offline”; optionally, the terrain model 3D can be calculated by the evaluation unit itself 12 immediately—that is, “online”- and the terrain model 3D can be recorded in memory 15.

(13) As is shown in FIG. 2, the laser scanner 10 comprises a measuring unit 16, which measures the height a of the vehicle 1 above the ground 2. To accomplish this, the measuring unit 16 can use every measurement principle known in the art, e.g., a photogrammetric distance measurement method. In the example shown, the measuring unit 16 emits a measurement beam 17, e.g., a radar, laser, or sonar measurement beam, e.g., vertically downward, and measures its height a (FIG. 4a)—and thus that of the laser scanner 10 or of the vehicle 1—above the ground 2 by measuring the time-of-flight of the measurement beam 17 that has been reflected off the ground 2 and received. Through a wire 18, the measuring unit 16 sends the value of the measured height a to a actuation device 19.

(14) The actuation device 19 comprises a controller 20 and an actuator 21 controlled by this controller 20. The actuation device 19 or its actuator 21 is anchored to vehicle 1 so that it is rigid to movement with respect to the vehicle 1. The controller 20 can optionally be a part of the evaluation unit 12.

(15) The actuation device 19 receives the height a above ground measured by the measuring unit 16, and, depending on this height a, it now rotates the fan-shaped scan pattern 6 of the scanning unit 11 with respect to the vehicle 1 about a first actuation axis 22, which is different from the scan axis 5, by a first actuation angle α, i.e., α=f(a). In the example shown in FIG. 2, this first actuation axis 22 is essentially vertical.

(16) FIG. 3 illustrates the effect of this rotation: Suitable rotation of the fan-shaped scan pattern 6 about the first actuation axis 22 depending on the height a keeps the strip width w of the scanning strip 7 constant even when the mountain 9 is overflown. This makes it possible to scan the ground 2 with simple, adjacent flight paths or routes, and to do so without gaps and with uniformly good scanning resolution. The scanning strips 7 of constant width w that are produced in this way are substantially simpler to combine for effective calculation of the terrain model 3D than is possible if the same ground 2 is scanned with the laser scanner 3 in FIG. 1.

(17) FIG. 4a through 4c show the example of FIG. 3 in detail. The ground 2 beneath the airplane 1 runs, e.g., in a first area A.sub.1 approximately at sea level (0 m) and, in a following second area A.sub.2, up the mountain 9 to a—highest—third area A.sub.3 at 1000 m. The airplane 1 flies in direction of motion 23 over all areas A.sub.1-A.sub.3 at a constant absolute height of, e.g., 2000 m. Despite the fact that the fan angle φ remains the same and despite the change in the height a above the ground, the strip width w of the scanning strip 7 remains constant in all areas A.sub.1-A.sub.3 (see FIGS. 4b and 4c), which is attributable to the height-dependent rotation of the fan-shaped scan pattern 6 about the first actuation axis 22. In the rear view shown in FIG. 4b, the projection φ′ of the fan angle φ changes from a smaller value in the first area A.sub.1 (α>>0, e.g., α=60°) to the full fan angle φ at the lowest height a above ground in the third area A.sub.3 (α=0), without the real fan angle φ ever needing to be changed; the top view of FIG. 4c illustrates this. In the third area A.sub.3 (α=0) the scan axis 5 is aligned, e.g., directly in the direction of motion 23 of the airplane 1.

(18) Returning to FIG. 2, the measuring unit 16 can be designed not only as a separate, stand-alone unit, but rather also in one of the following alternative types; the laser scanner 10 could possibly even have more than one of these alternatives and select the one which is most suitable for measuring the height a or combine the measurement results of multiple alternatives.

(19) According to one of these alternative variants, the measuring unit is formed by the scanning unit 11 itself, i.e., its measurement beam is one of the laser beams 4 emitted by the scanning unit 11 and reflected off the ground and received, e.g., a laser beam 4 emitted vertically downward. The controller 20 of the actuation device 19 can receive this information of the scanning unit 11 through a wire 24. If necessary, evaluation of the information, e.g., by the evaluation unit 12, can be interposed, so that in this variant the scanning unit 11—optionally together with the evaluation unit 12—forms the measuring unit.

(20) According to another alternative variant, the measuring unit comprises the satellite navigation receiver 13, which measures its three-dimensional position x/y/z, and thus the position of the laser scanner 10 or of the vehicle 1. With the help of the position x/y/z measured by the satellite navigation receiver 13 and a stored terrain model 3D′ of the ground 2 beneath the vehicle 1, the height a of the vehicle 1 above the ground is then determined.

(21) For this purpose it is possible to use, on the one hand, a fixed predefined terrain model 3D′ of the ground 2, this terrain model 3D′ being stored in a memory 25 of the laser scanner 10. It can be, e.g., a rough model of the ground 2 used for planning the scanning process, such as is commercially available in the form of a terrain model, e.g., from suppliers of navigation maps.

(22) On the other hand, in the case described further above in which the evaluation unit 12 itself calculates the terrain model 3D as the received laser beams 4 are evaluated (“online”), this calculated terrain model 3D can be used as the terrain model 3D′ for determining the height a, see data line 26.

(23) Each of the calculation steps required for measuring the height a from the position data x/y/z of the satellite navigation receiver 13 and the terrain model 3D′ can be carried out in its own functional block 27, which, however, can also be part of the controller 20 or even of the evaluation unit 12. That is, in these cases the measuring unit is formed by the satellite navigation receiver 13, the memory 25 or 15 with the terrain model 3D′ or 3D, and the functional block 27.

(24) As is shown in FIG. 2, the actuation device 19 can carry the entire scanning unit 11 on a movable arm 28 and rotate it with respect to the vehicle 1. Alternatively, the scanning unit 11 is pivotably mounted on the vehicle 1 or on a housing part of the laser scanner 10, and is merely rotated by the actuation device 19. According to another alternative embodiment, the actuation device 19 rotates the fan-shaped scan pattern 6 of the scanning unit 11 merely by adjusting a deflection mirror of the scanning unit 11 with respect to the vehicle 1. The deflection mirror can be inside or outside a housing of the scanning unit 11.

(25) FIGS. 5a and 5b show another possible way of adjusting the laser scanner 10 or its fan-shaped scan pattern 6 depending on the terrain course of the ground 2. The airplane 1 overflies a slope 29 in the ground 2 inclined transverse to the direction of motion 23 of the airplane 1. As is shown in FIG. 5a, this produces an asymmetric position of the scanning strip 7 with respect to the vertical line 30 under the airplane 1 (see the sections w.sub.1 and w.sub.r of the scanning strip 7), which also displaces the scanning strip in the direction transverse to the direction of motion 23.

(26) To counteract this, the actuation device 19 according to FIG. 5b is designed to use the terrain model 3D′ to determine the slope 29 of the ground 2 beneath the measured position x/y/z and transverse to the direction of motion 23 of the airplane 1. After that, the actuation device 19 rotates the fan-shaped scan pattern 6 of the scanning unit 11 with respect to the airplane 1 by a second actuation angle β, depending on the determined slope 29, about a second actuation axis 31 (FIG. 2) lying essentially in the direction of motion 23 (normal to the plane of the drawing of FIG. 5), to center the scanning strip 7 with respect to the vertical line 30. As is shown in FIG. 2, the second actuation axis 31 can coincide with the scan axis 5.

(27) In another optional embodiment, the pitch, roll, and/or yaw angles p, r, and y of the airplane 1 measured by the inertial measurement unit 14 of the laser scanner 10 can also be used to rotate the fan-shaped scan pattern 6 to compensate for at least one of these angles. The rotation about the first actuation axis 22 or the angle α can be used to compensate for the yaw angle y, that about the second actuation axis 31 (angle β) can be used to compensate for the roll angle r, and that about a third actuation axis 32 (angle γ) can be used to compensate for the pitch angle p.

(28) It goes without saying that in every embodiment the actuation device 19 sends the actuation angle/s α and, if present, β and γ through a corresponding wire 33 to the evaluation unit 12, and the evaluation unit 12 takes these angles α, β, γ into consideration in the determination of the emission directions of the laser beams 4, to create the terrain model 3D correctly.

(29) To make it simpler for the evaluation unit 12 to take into consideration the rotation of the fan-shaped scan pattern 6, the first actuation axis 22 and—if desired and present—also the second and/or the third actuation axes 31, 32 can intersect the scan axis 5 at the origin 34 of the fan-shaped scan pattern 6.

(30) The laser scanner 10 can be used from an airborne vehicle 1 both to scan a terrain and also to scan the floor of a body of water. To scan the floor of a body of water, the laser scanner 10 can be used in the same way on a suitable seaborne vehicle, i.e., a ship or submarine. Optionally, the vehicle 1 is unmanned, i.e., an unmanned aerial vehicle (UAV), unmanned surface vehicle (USV), or unmanned underwater vehicle (UUV).

(31) The disclosed subject matter is not limited to the presented embodiments, but rather comprises all variants, modifications, and combinations that fall within the scope of the associated claims.