Method and an apparatus for capturing three-dimensional data of an area of space

Abstract

In a method for capturing three-dimensional data of an area of space, a plurality of measuring beams (Ls) are sent out to a plurality of measuring points. A detector (50) receives a plurality of reflected beams (Lr) which are reflected by the measuring points (34a). A plurality of distances to the measuring points (34a, 34b) are determined as a function of the reflected beams (Lr). According to one aspect of the invention, at least one object (30) which comprises a hidden channel (66) having a visible entry opening (72) is located in the area of space. A rod-shaped element (32) is inserted into the channel (66) in such a manner that a free end proximal portion (70) protrudes from the entry opening (72). A first distance to a first measuring point (34a) and a second distance to a second measuring point (34b) are determined. An orientation (74) of the hidden channel (66) is determined as a function of the first and the second distances.

Description

CROSS REFERENCE

This is a U.S. national stage of application No. PCT/EP2007/005789, filed on 29 Jun. 2007. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §365(b) is claimed from German Application No. 10 2006 031 580.4, filed 3 Jul. 2006, the disclosure of which is also incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method for capturing three-dimensional data of an area of space, comprising the steps of:

• • providing a laser scanner having a transmitter and a receiver,
  • sending out a plurality of measuring beams by means of the transmitter to a plurality of measuring points in the area of space,
  • receiving a plurality of reflected beams which are reflected by the measuring points, and
  • determining a plurality of distances to the plurality of measuring points as a function of the reflected beams.

The invention also relates to an apparatus for capturing three dimensional data of an area of space, comprising a laser scanner having a transmitter and a receiver, the transmitter being configured for sending out a plurality of measuring beams to a plurality of measuring points in the area of space, the receiver being configured for receiving a plurality of reflected beams which are reflected by the measuring points and for determining a plurality of distances to the plurality of measuring points as a function of the reflected beams.

Such a method and such an apparatus are known, for example, from DE 103 61 870 B4.

This document discloses a laser scanner comprising a measuring head which holds a rotor rotatably supported. The rotor is rotated about a horizontal axis whilst sending out a plurality of laser beams. Due to the rotation of the rotor, the laser beams are sent out into a plurality of directions in space which cover an elevation angle of 270° or more. In addition, the measuring head is rotated about a vertical axis so that the laser beams sent out almost completely scan the surrounding area of space. In the measuring head, a receiver is arranged which receives the reflected beams reflected from object points in the area of space and which determines the distances to the object points by means of a difference in delay time between the beams sent out and the received beams. In addition, the receiver generates for each measuring point a gray scale value which depends on the intensity of the reflected measuring beam. Altogether, this known laser scanner can be used for recording a three-dimensional image of an area of space, the plurality of gray scale values producing an all-rotund image which is comparable to a black/white recording of the area of space. In addition, a distance information item is provided for each measuring point so that the area of space can be examined more accurately, surveyed and/or documented later by means of the recorded data. A typical application for such a laser scanner is the surveying of factory halls in which, for example, a new production line is to be planned and set up. In another known application, such a laser scanner is moved through a tunnel tube (if necessary without rotation about the vertical axis) in order to check, e.g., the state of the tunnel and determine the clear width at every point in the tunnel.

In principle, such a laser scanner is suitable for capturing three-dimensional data of any area of space which is bounded by objects such as walls or natural obstacles. The relatively fast and extensive data acquisition including an “optical image” of the area of space in an all-round view also allows such a laser scanner to be advantageous for forensic applications, i.e. the coverage and documentation of crime scenes. However, forensic coverage of a crime scene requires further information which cannot be supplied by laser scanners hitherto known. This includes primarily information about the location and the course of bullet channels produced when a projectile penetrates into a wall or into another obstacle.

For the forensic coverage of bullet channels, rods marked with end portion 68 (best seen with reference to FIG. 2) into the opening of the channel. At the free a freely protruding proximal end portion 70 (best seen with reference to FIG. 2) of the rod-shaped element 32, a body in the form of a sphere 34 is arranged here.

Reference number 36 designates a person who stands at a position in the area of space 38 from which a shot has presumably been fired, the projectile of which has created the hidden channel in the object 30. This position can be determined from the orientation of the hidden channel by means of the novel method and the novel apparatus.

FIG. 2 shows the laser scanner 10 and the rod-shaped element 32 in further detail. Identical reference symbols designate the same elements as before.

The measuring head 12 has a base 40 on which two support walls 42, 44 are arranged vertically. The support wall 42, together with a housing part 46, forms an internal space in which a light transmitter 48 and a detector 50 are arranged. The light transmitter 48 is here a laser diode, the detector 50 comprises a plurality of light-sensitive elements in a matrix-type arrangement.

Reference number 52 designates an evaluation and control unit which contains a PC-based computing unit in a preferred embodiment. The evaluation and control unit 52 drives the light transmitter 48 in such a manner that it generates a modulated measuring beam Ls. In addition, the evaluation and control unit 52 reads out the detector 50 for determining the distance d and the light intensity of the reflected light beam Lr.

The rotor 20 here carries a mirror 54 which is arranged opposite the transmitter 48 and the detector 50 and which is inclined by 45° with respect to the latter. The rotor 20 is connected to a drive 56 which produces a rotation of the mirror 54 about the horizontal axis 22. Due to this rotation, the measuring beam Ls is deflected along a vertical circular area in the area of space 38.

As already mentioned with respect to FIG. 1, the laser scanner 10 of the present embodiment has a further drive 58 which provides for a rotation of the measuring head 12 about the vertical axis 16. This allows the “vertical fan” spanned by means of the measuring beam Ls to be rotated within the area of space 38 so that the measuring beam Ls can illuminate virtually all object points in the environment of the laser scanner 10. In order to be able to correlate the distance and intensity information with the individual measuring points 28, the drives 56, 58 are provided with encoders 60, 62 by means of which the respective alignment of the measuring beam Ls is determined.

Reference number 66 designates a hidden channel in the object 30, for example a wall. According to an illustrative embodiment of the invention, the distal end portion 68 of the rod-shaped element 32 is pushed into the channel 66. The proximal end portion 70 of the rod-shaped element 32 protrudes from the entry or exit opening 72 of the channel 66. At the proximal end portion 70, two spheres 34a, 34b are arranged here as will still be described in greater detail by means of FIG. 3 in the text which follows.

The rod-shaped element 32 defines a longitudinal axis 74 which corresponds to the orientation of the hidden channel 66. This orientation can be determined in an automated manner by means of the two spheres 34a, 34b by determining the position of the two spheres 34a, 34b by means of the laser scanner 10. The positions of the spheres can be used for determining a vector which represents the orientation 74.

FIG. 3 shows a preferred embodiment of the rod-shaped element 32. The element 32 has a distal end portion 68 which is configured for being inserted into the hidden channel. At the proximal end portion 70, two spheres 34a, 34b are arranged at a defined distance dss. The outside diameter dr of the rod is here about 0.5 mm. By comparison, the outside diameter ds of the spheres 34a, 34b is of an order of magnitude of about 5 to 10 cm. However, the spheres 34a, 34b can also be smaller or larger, spheres having a larger diameter being more easily identified in the measurement data of the laser scanner 10. On the other hand, spheres having a smaller diameter facilitate the handling of the element 32 and provide for a lesser weight at the free freely protruding proximal end portion.

In one illustrative embodiment, the spheres 34a, 34b are of polystyrene and are pushed onto the rod of the rod rod-shaped element 32. The spheres 34a, 34b can be movable on the rod or can be fixed in their respective position, for example by bonding.

Each sphere 34a, 34b has a center point 76a, 76b of the sphere which is determined in preferred illustrative embodiments of the novel method. As shown in FIG. 3, the center points 76a, 76b of the spheres are here located on the longitudinal axis 74, i.e. the rod of the rod-shaped element 32 passes centrally through the center points 76a, 76b of the spheres.

FIG. 4 shows a further illustrative embodiment of a rod-shaped element 82 which, in principle, corresponds to the element 32 from FIG. 3. However, the element 82 has cubic bodies 84a, 84b instead of the spheres 34a, 34b.

FIG. 5 shows a further illustrative embodiment of a rod-shaped element 86 which has only a single cylindrical body 88 in contrast to the two previous illustrative embodiments.

In the text which follows, a preferred illustrative embodiment of the novel method is described by means of FIG. 6. After all components have been set up and taken into operation, the mirror 54 is positioned according to step 94. According to step 96, the measuring beam Ls is sent out. According to step 98, the reflected beam Lr is received. According to step 100, the evaluation and control unit 52 is then used for determining the distance to the measuring point 28 from the delay time difference. In addition, a gray scale value is determined from the intensity of the reflected beam Lr according to step 102. According to step 104, this is repeated for all positions of the mirror 54 which can be adjusted by means of the two drives 56, 58, in order to obtain a 3D recording of the area of space 38.

Once all measurement data have been recorded, the body or bodies on the rod-shaped element 32, such as, for example, the spheres 34a, 34b, is/are identified according to step 106. Following this, the coordinates of the center points 76a, 76b are determined according to step 108. In preferred embodiments, this is done by fitting ideal spheres into the “clouds of points” which were recorded by means of the laser scanner 10. For example, the fitting-in can take place in accordance with the method of least squares. Following this, the center point coordinates of the spheres fitted in are calculated.

From the center point coordinates calculated, the orientation 74 is determined according to step 110. Following this, the assumed position of the gunman who has fired a projectile which has formed the (bullet) channel 66 is determined according to step 112. For this purpose, a position or position range is sought along the orientation 74 at which a “typical height” above ground intersects the orientation 74. The typical height is within the range of between about 1 m and 1.80 m. As an alternative or additionally, the assumed position of the gunman can be determined by inserting an image of a person along the orientation 74 into the image of the area of space which was recorded by means of the laser scanner 10 (from the intensities of the reflected beams). In further illustrative embodiments, a person 36 can be recorded during the scanning of the area of space 38 so that the coordinates of the person 36 can be compared with the orientation 74.

Claims

1. A method for capturing three-dimensional data of an area of space, comprising:

providing a laser scanner comprising a transmitter and a receiver,

sending out a plurality of measuring beams (Ls) by means of the transmitter to a plurality of measuring points in the area of space,

receiving a plurality of reflected beams (Lr) which are reflected by the measuring points, and

determining a plurality of distances to the plurality of measuring points as a function of the reflected beams (Lr),

determining for each measuring point of the plurality of measuring points a gray scale value that depends on an intensity of respective ones of the plurality of reflected beams (Lr), and

recording a cloud of points, representative of the plurality of measuring points in the area of space, determined as a function of the plurality of distances and respective gray scale values,

wherein the area of space comprises at least one object which contains a hidden channel having a visible entry opening, a rod-shaped element being inserted into the channel in such a manner that a free end proximal portion of the rod-shaped element protrudes from the entry opening, a first distance the rod-shaped element comprising a defined geometric shape having a first three-dimensional coordinate and at least one second three-dimensional coordinate in the area of space, an ideal image of the geometric shape being matched to the cloud of points that represents measuring points of the geometric shape, the first three-dimensional coordinate to a first measuring point at the free end proximal portion and at least one second distance the at least one second three-dimensional coordinate to a second measuring point at the free end proximal portion being determined using the ideal image that is matched to the cloud of points that represent measuring points of the geometric shape, and an orientation of the hidden channel being determined as a function of a vector between the first and second distance three-dimensional coordinates.

2. The method according to claim 1, wherein the rod-shaped element has a rod-shaped distal area and a proximal area portion, the rod-shaped distal area portion being configured for insertion into the hidden channel and the proximal area portion having at least one enlarged body at which the first and second measuring points are arranged.

3. The method according to claim 2, wherein the distal area portion defines a longitudinal axis, and that the at least one body has a center point which is essentially located on the longitudinal axis.

4. The method according to claim 3, wherein a plurality of body distances to a plurality of measuring points at the at least one body are determined, and that the center point is determined as a function of the plurality of body distances.

5. The method according to claim 1, wherein each reflected beam (Lr) has a beam intensity, and the orientation is also determined as a function of the beam intensities.

6. The method according to claim 1 2, wherein the at least one body has an elongated shape, particularly a cylindrical shape.

7. The method according to claim 1, wherein the rod-shaped element comprises at least two bodies arranged at a relative distance (dss) from one another.

8. The method according to claim 7, wherein the at least two bodies are spheres.

9. The method according to claim 7, wherein the at least two bodies are cubes.

10. The method according to claim 1, wherein the hidden channel is a bullet channel, and an assumed position of a gunman within the area of space is determined as a function of the orientation.

11. The method according to claim 1 2, wherein the rod-shaped element comprises a marking in the distal area portion, which marking has more reflective and less reflective sections.

12. The method according to claim 1, wherein the rod-shaped element further comprises a rod-shaped distal area and a proximal area portion, the rod-shaped distal area portion being configured for insertion into the hidden channel and the proximal area portion comprising at least one enlarged body providing at least two measuring points which are different from one another.

13. An apparatus structured to capture three-dimensional data of an area of space, comprising:

a laser scanner having a transmitter and a receiver, the transmitter being configured for sending out a plurality of measuring beams (Ls) to a plurality of measuring points in the area of space, and the receiver being configured to receive a plurality of reflected beams (Lr) which are reflected by the measuring points and, to determine a plurality of distances to the plurality of measuring points as a function of the reflected beams (Lr), to determine for each measuring point of the plurality of measuring points a gray scale value that depends on an intensity of respective ones of the plurality of reflected beams (Lr), and to record a cloud of points, representative of the plurality of measuring points in the area of space, determined as a function of the plurality of distances and respective gray scale values, and

a rod-shaped element comprising a defined geometric shape,

wherein the receiver is also arranged configured for determining an orientation of a hidden channel at an object in the area of space, wherein a the rod-shaped element has a free end proximal portion which protrudes from an entry opening of the hidden channel,

wherein the receiver is configured for: matching an ideal image of the geometric shape to the cloud of points that represent measuring points of the geometric shape, the geometric shape having a first three-dimensional coordinate and at least one second three-dimensional coordinate in the area of space; determining a first distance the first three-dimensional coordinate to a first measuring point at the free end proximal portion and at least one second distance the at least one second three-dimensional coordinate to a second measuring point at the free end proximal portion using the ideal image that is matched to the cloud of points that represent measuring points of the geometric shape; and, determining the orientation of the hidden channel as a function of a vector between the first and second three-dimensional coordinates.

14. The apparatus according to claim 13, wherein the rod-shaped element further comprises a rod-shaped distal area and a proximal area portion, the rod-shaped distal area portion being configured for insertion into the hidden channel and the proximal area portion comprising at least one enlarged body providing at least two measuring points which are different from one another.