WO2016207442A1

WO2016207442A1 - Method and device for measuring an object surface in a contactless manner

Info

Publication number: WO2016207442A1
Application number: PCT/EP2016/064888
Authority: WO
Inventors: Anika Brahm; Gunther Notni; Peter KÜHMSTEDT
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2015-06-26
Filing date: 2016-06-27
Publication date: 2016-12-29
Also published as: DE102015211954B4; DE102015211954A1

Abstract

The invention relates to a device (1) and a method for measuring an object surface (2) in a contactless manner. In the method, a temperature distribution (15) on the object surface (2), said temperature distribution changing over time, is produced by imprinting at least one thermal pattern (9) onto the object surface (2). A respective thermal image of the object surface (2) is then simultaneously captured by each of at least two mutually spaced thermal image cameras (16, 17) at multiple successive capturing times such that a sequence of thermal image values are detected for points on an image plane (18, 19) of each of the thermal image cameras (16, 17). Corresponding points (20, 21) are then identified on the image planes (18, 19) of the thermal image cameras (16, 17), wherein a similarity between the sequence of thermal image values detected for the points of each pair is determined for pairs of potentially corresponding points on the basis of a mathematical similarity measure, and the similarity is maximized by varying at least one of the points of each pair. Spatial coordinates of the object surface (2) are then determined by means of triangulation on the basis of the identified corresponding points (20, 21).

Description

Method and device for non-contact measuring of an obiect surface

The invention relates to a method for the contactless geometric measurement of an object surface. Furthermore, the invention relates to a device for non-contact geometric measurement of an object surface, with which this method can be performed.

Methods for the contactless measurement of object surfaces are known per se. Such methods typically use a projector to project patterns onto a surface to be measured, and at least one camera to pick up the surface with the patterns projected thereon. Thus, for example, DE 10 2006 049 695 A1 describes a method in which fringe patterns are projected onto an object and two images of the object with the projected fringe patterns are recorded by two camera lenses arranged at a defined distance from one another in two different directions. so that for each pixel in the images of the object phase values can be determined. Based on this, corresponding pixels are identified in the images taken with the two camera lenses. Based on the mutually corresponding pixels, depth information for object points imaged on these pixels is then determined by triangulation. With this and similar prior art methods, surfaces of a variety of materials can be satisfactorily measured. In the case of highly reflective, transparent, translucent or strongly absorbing object surfaces, however, such known methods do not yield usable or only very inaccurate results. For objects made of a variety of technologically relevant materials, such as glass, metal or fiber composite material, and also for objects with smooth painted surfaces, these methods are therefore not suitable.

The object of the present invention is to propose a method which also allows transparent, translucent or strongly reflecting or absorbing object surfaces to be measured as simply and accurately as possible without contact. In addition, the invention has for its object to propose a corresponding device with which even such surfaces can be measured without contact.

This object is achieved by a method having the features of the main claim and by a device having the features of the independent claim. Advantageous developments emerge with the features of the dependent claims and the embodiments.

In the proposed method for the contactless measurement of an object surface, a time-variable temperature distribution on the object surface is produced by impressing at least one thermal pattern on the object surface. In this case, a thermal image of the object surface is simultaneously acquired by a plurality of consecutive acquisition times by each of at least two spaced-apart thermal imaging cameras, so that in each case a sequence of thermal image values is acquired for points in an image plane of each of the thermal imaging cameras.

Corresponding points in the image planes of the thermal imagers are then identified by determining similarity between the sequences of thermal south values recorded for the points of the respective pair for pairs of potentially corresponding points on the basis of a mathematical similarity measure and the similarity by varying at least one of the points each pair is maximized. Then Spatial coordinates of the object surface are determined by triangulation on the basis of the points identified as corresponding. Correspondingly, in the present document in each case points in the image planes of the different thermal imaging cameras are designated which are homologous in the sense that the same point on the object surface is imaged by the thermal imaging cameras on these points.

Although the measure of similarity used to determine the similarity of the consequences may or may not necessarily have all the characteristics of a metric in the strict sense of the word. It is only important here that the similarity measure is suitable for providing a measure of the similarity between value sequences which is suitable for finding as similar a sequence as possible. Of course, in the case of using a metric in the sense of the mathematical definition of the term, the mentioned maximizing of similarity would of course result from minimizing a distance defined by the metric.

Conveniently, the similarity between the sequences of thermal image values can be determined by evaluating a correlation function defined for pairs of value sequences, the corresponding points then being identified by maximizing or minimizing a value of a correlation thus formed. The correlation function can be chosen arbitrarily within wide limits and only has to show the characteristic typical of correlation functions of assuming an extremum - typically a maximum - for the identity of the sequences being compared by evaluating the correlation function, and the closer the extremes are compared to the more similar are.

By using thermal imaging cameras, unlike similar methods in which patterns are projected and recorded, the method is also suitable for measuring object surfaces which are transparent or translucent in the visible region of the electromagnetic spectrum or else highly reflective or absorbing. Namely, in surfaces of this kind, a projected light pattern in an image of an ordinary camera might either not be visible at all, because projected light would be too strongly absorbed or reflected in a direction unfavorable to the camera, or it would be backscattered Light effects in the camera, which come from deeper layers behind the object surface. Both would prevent a reliable identification of corresponding points and therefore also the correct determination of the necessary depth information by triangulation. This problem is solved in the inventive method in that instead of light patterns temperature distributions are used. On the one hand, these can be produced more easily on a surface area, even in the case of transparent or translucent materials, while light patterns inevitably penetrate deep into the material in these cases. On the other hand, recording with thermal imaging cameras also reliably allows images of the respective thermal

To create a patterned object surface when one would not be able to see enough or look too deeply into the material with a camera operating in the visible range, either due to unfavorable reflection or strong absorption.

In addition, the proposed type of survey has the advantage that the aufprojizierten pattern need not be known. Rather, the patterns can be chosen completely randomly and, in particular, be statistical or quasistatic in nature, provided that they are only sufficiently structured and distinct. Therefore, advantageously, the internal geometry of a device used to carry out the method need not be completely known. So it comes for example. in the case of using a projection device for generating the thermal patterns, not on their exact arrangement relative to the thermal imagers. This makes the method comparatively robust and in particular insensitive to tolerances in the structure of the device used. All in all, the triangulation is based on a very uncomplicated evaluation of the heat eggs. Accordingly, the proposed device for non-contact measurement of surfaces is correspondingly advantageous. The apparatus comprises a device for imparting thermal patterns to an object surface to be arranged for measurement in an object space, two spaced-apart thermal imaging cameras for capturing thermal images of the object surface in the object space and a control and evaluation unit for controlling the

Thermal imaging cameras and to evaluate the heat In this case, the control and evaluation unit is set up to control the thermal imaging cameras at a plurality of successive acquisition times for simultaneously acquiring a respective thermal image by each of the thermal imaging cameras so that a sequence of thermal image values is acquired for points in an image plane of each of the thermal imaging cameras. In addition, the control and evaluation unit is set up to identify corresponding points in the image planes of the thermal imaging cameras by determining a similarity between the sequences of thermal image values recorded for the points of the respective pair for pairs of potentially corresponding points on the basis of a mathematical similarity measure and the similarity Varying at least one of the points of each pair is maximized. Finally, the control and Auswerteeinhe ^'tt for determining spatial coordinates of the object surface by means of triangulation on the basis of identified as corresponding points is established. Thus, the device is advantageously suitable for carrying out the method described above.

The control and evaluation unit may e.g. be arranged to determine the similarity between the consequences of thermal image values by evaluating a correlation function defined for pairs of value sequences and to identify the corresponding points respectively by maximizing or minimizing a value of a correlation thus formed.

In order to reduce the search effort in identifying the corresponding points, it is possible to limit the points that potentially correspond correspondingly by taking advantage of the epipolar geometry. Thus, the variation of the at least one of the points can be limited to a limited area of the respective image plane, because as points corresponding only the points come into question, due to the other point and the internal geometry of the system of the two

Wäritddameras defined Epipolarlinien lie. Thus, the identification of the corresponding points can be effected, for example, by the fact that for each of a plurality of points in the image plane of a first of the thermal imaging cameras on a corresponding epipolar line in the image plane of a second of the thermal imaging cameras according to the corresponding

Point is searched by the used correlation function or the Similarity measure between the sequence of thermal image values, which has been detected for the respective point in the image plane of the first thermal imaging camera, and the sequences of thermal image values that have been detected for the points on the corresponding epipolar line in the image plane of the second thermal imaging camera is evaluated. The corresponding point can then be found as the point in the image plane of the second camera, for which the correlation or similarity formed in this way assumes the greatest value, for example, for which the correlation function assumes a maximum and thus the value of the correlation is maximized , In this case, the respectively corresponding point can be determined with subpixel precision, that is to say including subpixel interpolation.

Typically, the at least one imprinted thermal pattern is irregular, so that the time-varying temperature distribution shows an irregular spatial dependence. An irregular location dependency places fewer demands on imprinting the pattern than a regular structure. It is advantageous if the temperature distribution is not sufficiently constant in time as well as in space, so that on the one hand the thermal image values for a point change sufficiently strongly and on the other hand the consequences of thermal image values differ sufficiently from point to point. This allows a high accuracy of measurement can be achieved because the corresponding points can be reliably identified in the manner described. Therefore, the device for imprinting thermal patterns in expedient embodiments of the proposed device for generating at least one irregular thermal

Pattern set so that a producible by the thermal pattern temperature distribution on the object surface shows an irregular location dependence. It can be provided that at least one of the recording times is within a time interval during which no new thermal pattern is impressed on the object surface, so that the temperature distribution on the object surface changes between the preceding recording time and this at least one recording time by thermal diffusion. The temperature distribution on the object surface can therefore be at least one recording time in particular of distinguish the last imposed on the object surface thermal pattern. The fact that the temperature distribution on the object surface changes automatically, can be exploited in an advantageous manner to relatively easily and quickly sufficiently many sufficiently different thermal image pairs to capture, which can then be used to identify homologous points and triangulating.

As soon as a thermal pattern is impressed on an object surface, the temperature distribution through thermodiffusion takes a temporal development. As a rule, temperature differences between the warmer and colder areas of the surfaces are timed. In this case, unlike with the use of ordinary light patterns, capturing and imprinting does not necessarily have to be synchronized in time. In particular, a sufficiently strong temporal change of the thermal image values can be achieved, for example, by a one-time imprinting followed by subsequently at least two-dimensional acquisition of thermal images. Typically, an imprint is followed by multiple capturing. It is also conceivable that first of all a simultaneous imprinting and grasping takes place and subsequently several thermal images are recorded without renewed imprinting. Although it is not excluded that a new thermal pattern is applied before each detection, or that the detection and imprinting are fundamentally synchronous, each of these thermal patterns can also be applied if several thermal patterns are imprinted, after and possibly also when imprinted a plurality of thermal image pairs are recorded before the next thermal pattern is impressed.

The control and evaluation unit of the proposed device can additionally be set up to drive the device for imparting thermal patterns, in which case it is expedient in view of the explained possibility of utilizing thermal diffusion if the

Control and evaluation unit is arranged to control the means for imparting thermal patterns and the thermal imaging cameras so that at least one of the recording times is within a time interval during which the means for imprinting thermal patterns does not impose a new thermal pattern. The most recent imposition of a thermal pattern, on the other hand, may have already ended at this at least one recording time. The at least one thermal pattern can be impressed, for example, by a projection device. The named device for imprinting thermal patterns can thus be in particular a projection device. The imposition of the thermal pattern and thus the generation of the time-dependent temperature distribution with a projection device not only fits well with the non-contact character of the measurement. It also makes it possible to generate the time-dependent temperature distribution on which the measurement is based in a locally limited manner in a surface area and thus limit it to the object surface, at least to a certain extent. This in turn serves for the accuracy of the measurement, in particular in cases in which the material is not completely non-transparent for the heat radiation detected by the thermal imaging cameras.

Typically, the projection device has a radiation source for heating the object surface by means of electromagnetic radiation. This may be broadband or monochromatic, wherein a suitability of a radiation source may depend on the material of an object to be measured. Conveniently, a radiation source is used, which allows efficient heating of the material. In this case, the radiation sources can be set up for pulsed or continuous emission of the radiation power. In many cases the radiation source will be a laser.

Alternatively, the imprinting of the thermal pattern can also be done with non-optical methods. It is conceivable, for example, that the object surface is cooled in regions by spraying water drops. Alternatively, the object may also be immersed in a trough of small, heated and granular objects, such that the granular objects release heat to the object surface in contact areas and thus apply a thermal pattern to these impressions.

In the case of using a projection device, it may be expedient if it imprints the at least one optical pattern on the object surface by infrared radiation. The projection device expediently has a radiation source for generating infrared radiation. on. For example, the projection device may comprise a carbon dioxide laser emitting infrared radiation having a wavelength of about 10.6 μm. Such a radiation source is advantageous for measuring surfaces of glass, since many types of glass in this wavelength range have a high absorption coefficient, so that they are at a

Heat radiation through a carbon dioxide laser particularly efficient.

Since the measurement, unlike conventional pattern projection methods, is not based on a detection of reflection or scattering of electromagnetic radiation, but on an emission of electromagnetic radiation by the object to be measured and on a detection of the radiation thus emitted, a spectral range of the thermal imaging cameras used be selected or varied according to the emission wavelengths. Thus, the spectral range of the thermal imaging cameras used may be e.g. in the

Range of far infrared radiation between 5 μιη and 14 μηι or in the range of average infrared radiation between 3 μιη and 5 μιη lie. Depending on which temperature the time-dependent temperature distribution encompasses, under certain circumstances also a detection of electromagnetic radiation in the near infrared range or at wavelengths above

14 μιτι conceivable. For measuring, for example, a surface of an object made of glass, detection at wavelengths of more than 5 μm is advantageous, since many types of glass have no transparency in this wavelength range. Therefore, it can be achieved in this way that the radiation detected with the thermal imaging cameras originates from the surface of the object to be measured and does not come from the volume of the object. Sensitivities in the first-mentioned wavelength range, in turn, may also be advantageous in particular because particularly significant changes in the intensity of the thermal radiation occur in this wavelength range when heated by the thermal patterns starting from standard room temperatures. It is possible, but not necessary, for the sensitivity range of the thermal imaging cameras to coincide with the spectrum of a projection device used to generate the thermal pattern, or even to overlap with it.

The recorded thermal image values can be in the form of temperatures. Alternatively, the thermal image values may be in the form of radiation intensities or wavelengths or other parameters of the measured electromagnetic radiation resulting from the radiation intensities and / or wavelengths.

It can be provided that the projection device has an optical element for the spatial and / or temporal modulation of an electromagnetic radiation emitted by the projection device into the object space. For example, the optical element may be designed as a diffusing screen, through which the electromagnetic radiation is transmitted and / or reflected. A diffusing screen is suitable for distributing the electromagnetic radiation in such a way that the temperature distribution occurring on the object surface as a result of heating shows an irregular spatial dependence. Alternatively, a reflection and / or transmission of the electromagnetic radiation on a grid or a differently shaped mask or on a free-form element, e.g. a free-form mirror, done. A temporal modulation of the thermal pattern can be achieved for example by a rotation or displacement of the optical element and / or by moving the radiation source. The temporal modulation can be carried out arbitrarily within wide limits and does not have to follow a known pattern in the proposed method. Rather, statistical or quasi-statistical modulations of the thermal patterns are also suitable for generating sufficiently diverse temperature distributions on the object surface.

Embodiments of the invention will be described below with reference to the drawings. Show it

1 is a schematic plan view of a device for non-contact measurement of an object surface and an object,

2 is a schematic plan view of another device for non-contact measurement of an object surface and an object, Fig. 3 is a schematic representation of an impressed on an object surface thermal pattern and

4 shows a temperature distribution on the object surface after a development over time.

1 shows an embodiment of a device 1 for the contactless measurement of an object surface 2 of an object 3 in an object space 4. The device 1 comprises a device 5 for impressing thermal patterns

9 on the object surface 2 of the object 3. The device 5 is a projection device and comprises a radiation source 6, for example a carbon dioxide laser, and an optical element 7 in the form of a reflective element, which leads to an intensity modulation of the radiation and through a grating, a diffusing screen or a free-form element can be given. The carbon dioxide laser emits infrared radiation 8, which is reflected or diffracted at the optical element 7 and then hits the object surface 2 and heats it.

The object 3 to be measured is made of silicate glass, and the surface of the object 3 is heated by the infrared radiation 8 reflected or diffracted at the optical element 7, so that a spatially irregular thermal pattern 9 is impressed on the object surface 2. The irregular thermal pattern 9 may be, for example, a speckle pattern.

Another embodiment of a device 1 with a projection device 5 is shown schematically in FIG. Recurring features are given the same reference numerals in this and in the following figures. In this embodiment, the projection device has a transmissive optical element 10, which again may be a grating, a diffusing screen or a free-form element and which is arranged between the radiation source 6 and the object surface 2. In this case, the radiation source 6 generates an infrared radiation 8 which impinges on the optical element 10, is transmitted through it and is modulated thereby. The infrared radiation 8 generated by the radiation source 6 strikes after passing through the optical element

10 on the object surface 2 and heats them in the form of a spatially irregular thermal pattern. 9 In addition, the device 1 has a computer 11 with a control and evaluation unit 12. The projection device 5 is controlled by the control and evaluation unit 12. This determines the time points at which thermal patterns 9 are impressed on the object surface 2.

In addition, the control and evaluation unit 12 is set up for moving the optical element 7, 10, so that the thermal pattern 9 is spatially and temporally modulated by the control and evaluation unit 12. An imprinted thermal pattern 9 is shown schematically in FIG. 3 by way of example. The thermal pattern 9 consists of spatially irregularly arranged areas 13 of the object surface 2 with high temperature and areas 14 of the object surface with low temperature. After switching off the radiation source 6, a temperature distribution impressed by the thermal pattern 9 develops over time by a heat conduction in the

Object 3. FIG. 4 shows schematically a resulting temperature distribution 15 on the object surface 2 after a time of, for example, one second or a few seconds has elapsed. The device 1 also includes a first thermal imaging camera 16 and a second thermal imaging camera 17. The thermal imaging cameras 16, 17 are sensitive to electromagnetic radiation in the IR range, for example for thermal radiation in a wavelength range between 7.5 μηη and 14 μιτι. The thermal imaging cameras 16, 17 are arranged at a distance from one another and are likewise controlled by the control and evaluation unit 12. The first thermal imager 16 and the second thermal imager 17 are arranged and aligned to simultaneously measure the temperature distribution 15 in at least a portion of the object surface 2 in their respective image planes 18, 19, i. by a simultaneous recording each of a thermal image, can capture. For this purpose, the intensity of thermal radiation 22 measured in points 20, 21 in the respective image planes 18, 19 is evaluated.

When the respective thermal images are acquired simultaneously, a point 23 of the object surface 2 is imaged onto a first point 20 in the image plane 18 of the first thermal imaging camera 16 and onto a second point 21 in the image plane 19 of the second thermal imaging camera 17, as in FIG. 2 is shown. Of the first point 20 and second point 21 form a pair of corresponding points.

After imprinting the thermal pattern 9, the control and evaluation unit 12 controls a shutdown of the radiation source 6 by closing a shutter and triggers a simultaneous detection of thermal images by the thermal imaging cameras 16, 17. Thereafter, the temperature distribution 15 on the object surface 2 develops by thermal conduction to the temperature distribution 15 shown in FIG. 4, and the control and evaluation unit 12 triggers a repeated simultaneous simultaneous acquisition of thermal images with the radiation source 6 switched off. The described steps of imprinting a thermal pattern 9 and acquiring thermal images may be repeated one or more times with different thermal patterns 9. The time-dependent temperature distribution 15 generated by the impressed or impressed thermal pattern 9 can also be detected during the application of the at least one thermal pattern 9, that is to say without prior closing of a shutter. In this case, it may be advantageous to ensure, by means of filters impermeable to radiation of the radiation source 6 or by a sensitivity spectrum of the thermal imaging cameras 16, 17 which does not encompass the wavelength of this radiation-in the present example, ie, 10.6 μm-that only those of the If a sufficient number of different thermal patterns 9 are impressed, it may also be sufficient if only one pair of thermal images is recorded for each imprint it during the imprinting, be it shortly afterwards. It is also possible to take in each case at least one thermal image pair during the imprinting of the thermal pattern 9 or each of the thermal patterns 9 and in each case one or more times detecting thermal image pairs after closing the shutter and possibly before imprinting the next thermal

Pattern 9. The respective heat sources are buffered on a data memory 24 so that a sequence of temperature values is stored thereon for each point in the image planes 18, 19 of the thermal image cameras 16, 17.

In a next step, the control and evaluation unit 12 compares the recorded sequence of temperature values for each point 20 in the image plane 18 of the first thermal imager 16 with the sequences of temperature values of the points in the image plane 19 of the second thermal imaging camera 17 to identify the corresponding points 20, 21. The control and evaluation unit 12 confines itself to finding the point 21 in the image plane 18 of the first thermal imaging camera 16 corresponding point 21 in the image plane 19 of the second thermal imaging camera 17 to points in the image plane 19 of the second thermal imaging camera 17, on a through the point 20 are in the image plane 18 of the first thermal imaging camera 16 epipolar line.

The pairs of sequences of temperature values are compared by the control and evaluation unit 12 using a correlation function assigning a similarity value to each of the pairs of sequences, the similarity value taking a large value for a pronounced similarity of the sequences and a low value for very different sequences. One after the other, the control and evaluation unit 12 evaluates the sequences for potentially corresponding points in pairs, and maximizing the similarity value, the actually corresponding points 20, 21 can be found in the image planes 18, 19 of the two thermal imaging cameras 16, 17. In another definition of the correlation function, it is also conceivable that the corresponding points 20, 21 are found by minimizing rather than maximizing a similarity value.

Subsequently, the control and evaluation unit 12 determines spatial coordinates of points 23 on the object surface 2 on the basis of the previously found corresponding points 20, 21 in the image planes 18, 19 of the two thermal imaging cameras 16, 17. For this purpose, it is utilized that the relative position of the thermal imaging cameras 16, 17, the spatial coordinates being determined thereon by triangulation.

Claims

claims

Method for the contactless measuring of an object surface (2) with the following steps:

Generating a temporally variable temperature distribution (15) on the object surface (2) by impressing at least one thermal pattern (9) on the object surface (2),

in each case simultaneously acquiring a thermal image of the object surface (2) by each of at least two spaced-apart thermal imaging cameras (16, 17) at a plurality of successive acquisition times, so that for points in an image plane (18, 21) each of the thermal imaging cameras (16, 17 ) in each case a sequence of thermal image values is detected, identifying corresponding points (20, 21) in the image planes

(18, 21) of the thermal imaging cameras (16, 17) by determining, for pairs of potentially corresponding points based on a mathematical similarity measure, a similarity between the sequences of thermal image values acquired for the points of the respective pair and the similarity by varying at least one of

Points of each pair is maximized,

- Determining spatial coordinates of the object surface (2) by triangulation on the basis of identified as corresponding points (20, 21).

2. The method according to claim 1, characterized in that at least one of the recording times is within a time interval during which no new thermal pattern (9) is impressed on the object surface (2), so that the temperature distribution (15) on the object surface ( 2) between the previous recording time point and this at least one recording time changed by thermal diffusion.

Method according to one of claims 1 or 2, characterized in that the at least one impressed thermal pattern (9) is irregular, so that the time-varying temperature distribution (15) shows an irregular location dependence.

Method according to one of claims 1 to 3, characterized in that the similarity between the sequences of thermal image values is determined by evaluating a correlation function defined for pairs of value sequences and the corresponding points (20, 21) respectively by maximizing or minimizing a value of a thus formed Correlation can be identified.

Method according to one of claims 1 to 4, characterized in that the at least one thermal pattern (9) by a projection device (5) is impressed.

A method according to claim 5, characterized in that the projection device (5) imprints the at least one thermal pattern (9) by infrared radiation (8) on the object surface (2).

Device (1) for contactless measuring of surfaces (2), comprising means (5) for impressing thermal patterns (9) on an object surface (2) to be arranged in an object space (4) for measurement, two spaced apart thermal imaging cameras (16, 17 ) for recording thermal images of the object surface (2) in the object space (4) and a control and evaluation unit (12) for driving the thermal imaging cameras (16, 17) and for evaluating the thermal images recorded thereby, wherein the control and evaluation unit (12) is set up to do the following:

- Driving the thermal imaging cameras (16, 17) for simultaneously detecting a respective thermal image by each of the thermal imaging cameras (16, 17) at a plurality of successive recording times, so that for Points in an image plane (18, 19) of each of the thermal imaging cameras (16, 17) a sequence of thermal image values is detected in each case,

Identifying corresponding points (20, 21) in the image planes (18, 19) of the thermal imaging cameras (16, 17) by making a similarity for the pairs of potentially corresponding points on the basis of a mathematical similarity measure between the sequences of thermal image values acquired for the points of the respective pair is determined and the similarity is maximized by varying at least one of the points of the respective pair,

- Determining spatial coordinates of the object surface by triangulation on the basis of identified as corresponding points (20, 21).

Device (1) according to claim 7, characterized in that the control and evaluation unit (12) is also designed to drive the device (5) for impressing thermal patterns (9) and is further arranged, the means (5) for imprinting thermal Control pattern (9) and the thermal imaging cameras (16, 17) so that at least one of the recording times in a time interval during which the means (5) for impressing thermal patterns (9) does not impose a new thermal pattern (9).

Device (1) according to one of claims 7 or 8, characterized in that the device (5) for impressing thermal patterns (9) is a projection device (5).

Device (1) according to claim 9, characterized in that the projection device (5) has a radiation source (6) for generating infrared radiation (8).

Device (1) according to one of claims 9 or 10, characterized in that the projection device (5) an optical element (7; 10) for the spatial and / or temporal modulation of one of the projection device (5) in the object space (4) radiated electromagnetic radiation (8).

12. Device (1) according to one of claims 7 to 11, characterized in that the device (5) for imprinting thermal patterns (9) for generating at least one irregular thermal pattern (9) is arranged so that one by the thermal pattern (9) producible temperature distribution (15) on the object surface shows an irregular location dependence.

13. Device (1) according to one of claims 7 to 12, characterized in that the control and evaluation unit (12) is arranged to determine the similarity between the sequences of thermal image values by evaluating a defined for pairs of value sequences correlation function and the corresponding Each identify points (20, 21) by maximizing or minimizing a value of a correlation thus formed.