EP2211715A1

EP2211715A1 - High-resolution optical detection of the three-dimensional shape of bodies

Info

Publication number: EP2211715A1
Application number: EP07846669A
Authority: EP
Inventors: Dirk Rutschmann; Rene Pfeiffer
Original assignee: corpuse AG
Current assignee: corpuse AG
Priority date: 2007-11-19
Filing date: 2007-11-19
Publication date: 2010-08-04
Also published as: WO2009065418A1; US20100296726A1; US8363927B2

Abstract

The invention relates to a cost-efficient method and an arrangement for the 3D digitization of bodies and body parts, which creates dense and exact spatial coordinates despite imprecise optics and mechanics. The body to be digitized is placed onto a photogrammetrically marked surface, a photogrammetrically marked strap is applied to the body or body part to be digitized, and a triangulation arrangement comprising a camera and light pattern projector is moved on a path around the body. Through the photogrammetric evaluation of the photogrammetric marks of the surface and the strip located in the image field of the camera and the light traces of the light projector on the marked surface and the marked strip, all unknown inner and outer parameters of the triangulation arrangement are determined, and from the light traces on the unmarked body the absolute spatial coordinates of the body or the body part are determined with high pixel density and high accuracy, without separate calibration methods.

Description

High-resolution optical detection of the spatial form of bodies

The detection of the 3-dimensional spatial form of bodies or body parts, in particular of human body parts such as legs, torso and feet is an important component in the production or assignment of matching garments, orthopedic aids such as compression stockings, prostheses and orthoses as well as in the production or assignment matching shoes. There are numerous optical 3D scanners on the market, which usually either with the methods of laser triangulation (see eg PEDUS foot scanner of the company Vitronic Dr. Stein, www.vitus.de) or the stripe projection (see eg body scan of the company Breuckmann, www.breuckmann .com) work. Both methods are based on triangulation, i. a stable spatial triangular arrangement of light projector, camera and body for pointwise determination of the distance of the observed body surface of the triangulation of camera and light projector, also called measuring head. From the sum of these distance data, an XYZ point model of the considered surface is determined. In order to capture the entire body, either several camera / projector arrangements have to be mounted or moved around the body (eg in the body scan of the Breumann company) or a camera / projector arrangement has to be moved mechanically over the body surface (eg in the case of Foot scanner PEDUS of the company Vitronic Dr. Stein).

The angle arrangement of camera / projector is sensitive: even small angle errors lead to large measurement errors in the measured distances. The movement of the triangulation arrangement in space is equally sensitive: small errors in the position determination of the measuring head lead to large measurement errors in the generated 3D point model. This sensitivity means that these scanners often have to be recalibrated even with a very robust and expensive opto-mechanical design, especially after each transport and every movement of the Scanner. Since these scanners often also carry the weight of the customer (eg pedus foot scanner), the requirement for a rigid construction can be achieved only with considerable effort, so that the calibration must be repeated often from this point of view.

Calibrating one on the laser or laser triangulation

Strip projection working 3D scanners using different standards provides a large number of parameters, which directly determine the measurement accuracy. These are, for example:

the exact position between camera and projector (triangulation angle, measuring base, mutual alignment, ...)

- the exact internal parameters of camera and projector (focal lengths, sensor dimension, geometry of the pixels, tilt and rotation angle of the laser line projector ...)

- The exact spatial positions of the triangulation arrangement at each measurement recording, the so-called external parameters.

Therefore, the calibration of a 3D scanner is a complex process to be performed with the aid of high-precision calibration bodies, in which the sales personnel are e.g. of an orthopedic specialty store is often overwhelmed and therefore rejected.

Due to the required mechanical stability, these 3D scanners can not be offered very cheaply, so that many potential applications of so-called mass-customization (the production of individually fitting clothing, etc.) are currently not being implemented because of the high costs of the 3D scanners.

The company corpus.e AG (www.corpus-e.com) has the name

"Lightbeam®" has developed a photogrammetric foot scanner that works without a projector and thus without a sensitive triangulation arrangement, whereby the foot is covered with a specially marked elastic sock and a video camera is mechanically moved around the foot (see also WO 2004/078040 A1). The foot stands on a photogrammetrically marked surface, so that the spatial position, from which the camera measures, permanently can be determined automatically with the methods of photogrammetry (the so-called "outer" parameters of a photogrammetric measuring arrangement). Likewise, the so-called "internal" parameters of the camera itself, such as focal length, image sensor, optical axis penetration point, object distortion, etc., can be determined automatically from the evaluation of overlapping 2D images of the marked surface and the marked foot. It can be commissioned at any time after a transport without calibration, it never needs to be recalibrated after a load change, the mechanical stability of the design can be simple and inexpensive as it does not feed into the end result, the 3D model being measured.

There is, however, an inherent disadvantage of this otherwise powerful process: due to the design limited density of the photogrammetric markings on the elastic sock, the density of the generated XYZ point cloud is significantly lower than a laser or fringe projection method (typically 4000 XYZ points vs. approx. 1 million XYZ points). While this lower point density is not a disadvantage in flat body parts such as the upper foot, it is critical in the area of high curvature of space such as toes, heel, transition from upper to foot to sole, and so forth.

The requirement that the body to be measured must be clothed with a photogrammetrically marked elastic coating is another disadvantage. Such coatings are not easy to produce; Several sizes and shapes are needed depending on the body part, such as the trunk, legs, feet and so on.

It may also be important that e.g. digitizing feet for the

Selection of suitable ski boots, the customer keeps his own winter socks, so that this is taken into account in the form adaptation. However, it is not possible to photogrammetrically mark any sock with simple means. - A -

There is therefore a high economic and technical interest in providing a 3D digitizer that does not need to be laboriously calibrated and produces a density of spatial points without having to use a photogrammetrically marked elastic coating. The 3D digitizer should therefore be inexpensive, high-resolution and calibration-free, or self-calibrating.

This is inventively achieved by a method having the features of claim 1 and an arrangement according to claim 12. By evaluating the photogrammetric marks of the surface and the marks on the body and the light pattern of the at least one light projector on the marked area and in the area of the marks on the body, the inner and outer parameters of the at least one triangulation arrangement for each recording position are determined during each recording process. Thus, all internal and external parameters of the existing camera and light projector measuring head can be automatically determined by photogrammetric method and simultaneously with the actual 3D measurement, without the need for its own, complicated calibration procedure with calibration body. The parameters of the camera are determined by evaluating the photogrammetric marks and the parameters of the triangulation arrangement by evaluating the position of the light track on the marked area and the marked body area in relation to the marks. Using the parameters thus determined, the 3D spatial shape of the body or body part is then determined by photogrammetric methods by evaluating the position of the light pattern on the body or body part in the images taken by the at least one camera. Since the parameters are each determined, the requirements for the stability of the triangulation are low and the mechanical guide and the drive can be made very simple and inexpensive, since their mechanical accuracy is not incorporated into the accuracy of the photogrammetric determination of the camera position.

In order to achieve stable values for the self-calibration, it is advantageous if photogrammetric marks are distributed over the entire image field. However, it is cumbersome for a simple and easily accessible digitizer to arrange further marked areas in the background of the upper image field. The Depth of field would not be enough and the entire volume of the 3D digitizer would be too big for many orthopedic businesses. According to the invention therefore photogrammetric marks are placed in a portion of the body in the upper region, in a preferred embodiment, these photogrammetric marks on a narrow, elastic band, which in turn is attached to the body or body part itself in the upper area, ie so that the band as possible far from the marked area. The multiple registration of the marks on the surface and band allow a much more stable bundle compensation and thus a more robust calculation of the internal and external parameters of the camera. The marked band is also required to determine a possible tilt angle of the light line of the projector. The mark in the form of an inexpensive narrow band is compared to the complete clothing of the entire body with a photogrammetrically marked elastic coating a great simplification. In addition, the surface of the body / body of interest actually remains free for a high-resolution 3D digitization according to the number of light sections analyzed and leads therefore generating a very dense XYZ point cloud of the body to be digitized. Of course, other forms of application of the brands as over a tape conceivable.

In order to obtain a calibration-free or self-calibrating 3D digitizer, which preferably operates according to the light-slit method, knowledge of the internal and external parameters of the camera alone is not sufficient. It is also necessary to know the spatial positions of the light line projector mounted with the camera in a triangulation arrangement, in particular the angle between the optical axis of the camera and that of the projector, the vertical spatial position of the projected light line, and the distance camera projector, the so-called measuring base of the triangulation.

These unknown parameters are achieved according to the invention by evaluating the positions of the light tracks in the camera images, which generates the projected light line on the marked area and the marked band, or in the region of the attached marks.

According to the invention, the entire 3D Digtalizer is inexpensive to produce by this self-calibration, since all mechanical components simple and only with moderate mechanical stability and accuracy must be designed and produced.

Since the photogrammetric self-calibration is carried out continuously with the actual digitization of the foot, so that the inventive goal of a very low-cost, self-calibrating and high-resolution 3D digitizer is achieved, which except for an additional photogrammetric marks on the body, for example, attached with a simple elastic band, without photogrammetric marking of the body to be digitized.

Another advantage is that the photogrammetric marks of the area and on the body (preferably on a belt) can be designed purely in b / w. The projected light pattern or the light line can be easily recognized in the image of a b / w camera due to their high brightness. The method according to the invention therefore does not require a color camera, which in turn represents a considerable simplification and cost reduction.

It goes without saying that the method according to the invention can be used not only for biological but also for technical or artistic bodies, e.g. for the digitization of artistically valuable sculptures, casting bodies, etc. The inventive concept also covers methods in which the light projector not only has a simple line, but more complex light patterns such as e.g. generated several parallel lines, color or b / w coded lines. Such light pattern projectors are known to those skilled in image processing.

Furthermore, it is also known to design a triangulation measuring head such that a light pattern projector is arranged on each side of a single camera; As a result, in particular concave spatial forms can be better detected.

Advantageously, the triangulation probe may also be hand-held, i. Without mechanical guidance to be moved around the body to be digitized, only care must be taken that the field of view of the camera at each

Recording position from the marked area over to be digitized

Body up to and including the marks on the body is enough, even if it is Depending on the body shape can give individual recording positions in which the tape is covered.

Essential for the inventive idea is that on the inventive

Method of self - calibration of the moving camera and the moving light projector, all internal and external parameters of the entire measuring head and the entire structure automatically based on the evaluation of the

Camera in addition to the light line with recorded photogrammetrically marked area and preferably used photogrammetric

Bandes and the light track of the light projector on the marked area and the marked band continuously and simultaneously with the 3D scanning of the

Body are determined and thus no expensive separate calibration for the digitizer according to the invention is needed.

The method and the arrangement according to the invention therefore permit the construction of very cost-effective yet accurate and high-resolution self-calibrating 3D digitizers in comparison with the prior art.

Further features and advantages of the invention can be found in the appended subclaims and become clear from the description of an application example which describes a 3D digitizer for a foot. We use the following illustrations:

FIG. 1 shows a basic arrangement according to the invention in FIG

Side view;

Figure 2 shows schematically an arrangement according to the invention in a plan view;

FIG. 3 schematically shows a detail of the arrangement according to FIG. 2 with twisted line-of-light projector;

FIG. 4 shows a detail of a marked band according to the invention with two lines of light lines.

The selected embodiment describes the 3D digitization of a

Foot, for example, for the production of a customized orthopedic shoe. FIG. 1 shows a photogrammetric marking in a side view

Surface 10 on which a patient stands, from which his feet 12 can be seen. Along a substantially circular guide 14 which is attached to a support 16, a triangulation assembly 18 with camera and light line projector can be mechanically moved around the patient. Instead of a light line projector, a projector that projects a more complicated pattern of light can also be used. The mechanical arrangement can be performed easily, even a movement of the triangulation arrangement by hand without guidance is possible. A narrow, preferably elastic, photogram metrically marked band 20 fits snugly against a leg above the foot to be digitized, it is of course also possible to attach a band to both feet, or to choose a different mounting method for the marks. The tape 20 is mounted so that it is located at the upper limit of the field of view just captured by the camera, that is detected in a region of the image field which is opposite to the marked surface, in order to obtain stable calibration values. Suitable automatically evaluable photogrammetric markings, which can be easily produced eg as knit textile, are described in EP 01 986759.7.

In the exemplary embodiment, it is a black and white camera and the shape and / or brightness design of the marks of the surface 10 and the belt 20 and the light pattern projector are selected so that they in the gray value images of the b / w camera with known methods the optical pattern recognition can be detected and distinguished. Likewise, it is possible to use a camera suitable for color and to select the colors of the photogrammetric marks of the area 10 and the belt 20 and the color or color of the light pattern projector so that they recognized and distinguished in the color images of the color camera with the methods of color classification can be.

In the case of a color camera, the colors of the photogrammetric marks of the area and the ribbon, as well as the color or color of the light pattern projector, as well as the shape and / or brightness of the marks of the area and the ribbon and of the light pattern projector can also be chosen to be in the color images of the camera can be detected and distinguished by the methods of optical pattern recognition. If the surface properties of the body are also to be determined, the light pattern projector is preferably alternately switched between a patternless illumination suitable for detecting surface properties of the body or body part to be digitized and a patterned illumination suitable for recognizing the spatial form of the body and / or body part to be digitized.

In the design of the photogrammetric marks, they can also be optically designed so that they reflect the light of the light pattern projector in a manner that can be distinguished automatically in the image of the camera with methods of image processing of the reflection of the body and / or body part, including the Light polarization can be used advantageously.

A projected light line 22 extends from the marked area 10 over the digitized, unmarked foot to above the marked band 20. The field of view of the camera is designed accordingly by selecting the focal length.

As the triangulation assembly 18 (or measuring head) is moved around the patient, an image pickup control 24, indicated in Figure 2, initiates a plurality of shots including both a portion of the marked area 10, a portion of the foot 12, and depict a section of the marked band 20. The recordings must overlap. The smaller the spatial recording distances are, the more accurate both the calibration and the digitization.

FIG. 2 shows in a top view the marked area 10 with photogrammetric marks 26, the triangulation arrangement 18 comprising the camera 28 and the light line projector 30, as well as the light line 22 generated by the light line projector and beginning on the marked area 10. Two arrows 32 indicate that the Camera 28 of the measuring head 18 detects a section of the marked area 10. An arrow 34 indicates the direction of movement of the triangulation arrangement. In addition to the already mentioned image acquisition control 24, a computer 36 is indicated, which evaluates the images of the camera. The feet 12 are shown schematically. Successive images have a large overlap area, so that the photogrammetrically marked marks 26 easily by a automatic recognition of their coding can be found in the individual recordings and assigned to each other. It is known to the person skilled in Photogramm metrie that this allows all internal and external parameters of the camera such as absolute position in space, focal length, position of the sensor in the camera, etc. can be determined.

FIG. 3 shows a section of the arrangement from FIG. 2 with the surface 10, a foot 12, marks 26 and the triangulation arrangement 18. A slight rotation of the light line projector 30 is indicated, with which the triangulation angle changes. As already stated, the accuracy of the measurement is very dependent on the triangulation angle. The rotation of the light line projector 30 in a plane parallel to the marked surface 10 results in a rotation of the light line 22 from a position 38 to a position 40 on the marked surface 10. This rotated light line is picked up by the camera 28 Rotation angle determined by evaluating the recordings.

FIG. 4 schematically shows a section of the marked band 20, as can be seen in the field of view of the camera 28. A tilting of the vertical alignment of the light line projector 30 leads to a tilting of the light line or light line 22 on the marked band 20 from a position 42 to a position 44, which is recorded by the camera 28. Again, the marks on the tape allow the absolute determination of the position shift.

Under the optically constructive easily achievable condition that the light line projector 30 generates a sufficiently straight line, the computer 36, to which the image data are forwarded, with a program for automatic photogrammetric determination by evaluating the photogrammetric marks 26 of the surface 10 and the Bandes 20 and the light pattern of the light projector 30 on the marked area 10 and the marked band 20, the internal and external parameters of the triangulation 18 for each picking position accurately calculate.

The automatic detection of the light line 22 in the image field of the camera 28 is known to those skilled in the image processing. The automatic detection of the photogrammetric marks 26 on the surface 10 and on the elastic band 20 are from the products, product descriptions, publications and disclosed property rights of corpus.e AG and are part of the general knowledge of the person skilled in the art. They therefore need not be explained here.

Claims

claims

1. A method for the precise optical detection of the 3D spatial form of bodies or body parts, comprising the following steps:

Positioning of the body or part of the body to be digitized (12) on a photogrammetrically marked area (10) with photogrammetric marks (26),

Attaching photogrammetric marks (27) in a partial region of the body or body part (12) to be digitized,

Moving at least one triangulation assembly (18) comprising at least one camera (28) and at least one light pattern projector (30) and characterized by inner and outer parameters around the body or body part to be digitized, the at least one camera being a series of shots and the light pattern projector projects a light pattern onto the body or body part, wherein each shot captures an image field that is from the marked area

(10) over the unmarked body or body part (12) to be measured,

the photogrammetric marks (27) are fastened to the body or body part (12) to be digitized in such a way that they are detected at least in the majority of the recordings,

- The photogrammetric marks (27) are attached to the digitizing body or body part (12) that they are detected in a region of the image field which is opposite to the marked surface (10), and

- the image fields of successive images overlap, evaluation of the photogrammetric marks (26) of the surface (10) and of the photogrammetric marks (27) and of the light pattern of the at least one light projector (30) on the marked area and in the area of the photogrammetric marks (27) for determining the internal and external parameters of the at least one triangulation arrangement (18) for each picking position,

Determination of the 3D spatial form of the body or body part (12) by photogrammetric methods using these parameters and by Evaluation of the position of the light pattern on the body or body part in the images taken by the at least one camera.

2. The method according to claim 1, characterized in that the photogrammetric marks (27) on at least one band (20) are applied, and the tape (20) is attached to the body.

3. The method according to claim 1 or 2, characterized in that the light pattern projector (30) projects a light line and the 3D spatial shape is determined by the light section method.

4. The method of claim 1, 2 or 3, characterized in that the camera (28) is color suitable and that the colors of the photogrammetric marks (26) of the surface (10) and the photogrammetric marks (27), and the color or colors of the light pattern projector (30) are selected so that they can be recognized and distinguished in the color images of the color camera with the methods of color classification.

5. The method according to claim 1, 2 or 3, characterized in that the

Camera (28) is a black and white camera and that the shape and / or brightness design of the mark (26) of the surface (10) and the photogrammetric marks (27) and the light pattern projector (30) are selected so that they can be detected and discriminated in the greyscale images of the b / w camera using optical pattern recognition techniques.

6. The method according to any one of claims 1 to 5, characterized in that the camera (28) is a color camera and that the colors of the photogrammetric marks (26) of the surface (10) and the photogrammetric marks (27) and the color or colors the light pattern projector (30) and the shape and / or brightness design of the marks of the surface and the band and the light pattern projector are selected so that they can be detected and distinguished in the color images of the camera with the methods of optical pattern recognition.

7. The method according to any one of claims 1 to 6, characterized in that the light pattern projector (30) alternately between a patternless to

Detection of surface properties of the digitizing body or body part (12) suitable lighting and a patterned, for detection the spatial form of the body to be digitized and / or body part switches suitable lighting.

8. The method according to any one of claims 1 to 6, characterized in that the photogrammetric marks (26) of the surface (10) and the photogrammetric marks (27) are optically designed so that they reflect the light of the light pattern projector in a manner which In the image of the camera can be distinguished automatically with process of image processing of the reflection of the body and / or body part.

9. The method according to claim 8, characterized in that the photogrammetric marks (26) of the surface (10) and the photogrammetric

Marks (27) affect the polarization of the light pattern projector differently than the reflective body and / or body part.

10. The method according to any one of the preceding claims, characterized in that the triangulation arrangement (18) is manually guided around the body to be digitized.

11. The method according to any one of the preceding claims, characterized in that the body and / or body part (12) is a living or dead biological body.

12. The method according to any one of claims 1 to 10, characterized in that the body and / or body part is a technical and / or inanimate body.

13. Arrangement for carrying out the method according to one of claims 1 to 12, comprising a surface (10) which is provided with photogram metrically evaluable marks (26) and on which a digitizing body or body part (12) can be positioned, a Triangulation assembly (18) comprising a camera (28) and a light pattern projector (30) photogramm metrically evaluable marks (27), which can be attached to the body or body part which is farthest from the marked surface (10), a moving device (14) for moving the triangulation device (18) around the body or body part to be digitized, and an image pickup controller (24) for triggering image pickups during the movement, wherein the image field of the camera is from the marked surface to be digitized Body or body part to the photogrammetric marks (27) ranges, a computer (36) to which the image data are forwarded with a program for automatic photogrammetric determination of all unknown internal and external parameters of the triangulation and the spatial shape of the body to be digitized and / or body part.

An assembly according to claim 13, characterized in that it further comprises a band (20) on which the photogrammetric marks (27) are applied and the band (20) can be attached to the body.

15. Arrangement according to claim 13 or 14, characterized in that the movement device by manual movement of the

Triangulation arrangement (18) is formed.