Method for evaluating at least one marker on physical object for metrology of detected object

Abstract

The invention relates to a method of evaluating at least one marker on a physical object for metrology of a detected object, comprising the steps of: providing at least one rendering of the marker, the at least one rendering each originating from sensor detection; determining a reference mark of the mark based on the rendering of the provided mark, wherein the reference mark has at least two partitions with different display attributes; the determination of the reference marker comprises the steps of: transforming to one or more color spaces of rendering of the provided marker in order to render at least two partitions having different display attributes with substantially the same display attribute; identifying a reference mark based on the partitions displayed with substantially the same display attribute; providing display of at least two partitions with different display attributes; at least one reference point of the reference mark is identified based on the provided displays having different display attributes.

Description

Technical Field

[0001] The present invention relates to a method for evaluating at least one marker on a physical object for metrological detection of the object. The present invention also relates to such a marker, a computer program, and a device for this purpose. Background Art

[0002] It is well known that photogrammetry can obtain certain information about a physical object from photographs. In many photogrammetry applications, several photographs can be combined to obtain a three-dimensional reconstruction having a number of defined three-dimensional points on the object.

[0003] It is also known that two-dimensional fiducial markers (markers or photogrammetric markers) can be attached to an object to define measurement points when measuring the object. Fiducial markers typically have a clearly defined reference point (usually the center of the shape) and a code for unique identification.

[0004] Fiducial markers can meet various different requirements. For example, it is important that they are recognized by computer vision systems. The false-positive rate and the false-negative rate should be kept as low as possible. Additionally, the specific 3D position of the fiducial marker should be invariant under various types of distortions such as perspective distortion, affine distortion, and lens distortion. The ability to provide various different unique identifiers (IDs) from a series of reference markers that can be recognized using the same computer vision method may also be crucial. At the same time, it may be critical that the decoding of the fiducial marker is robust and has a low error rate, even if they are partially occluded. Additionally, false-positive detection should be avoided, especially if the marker is reflected on the surface. When determining the reflection point of the marker, it should be emphasized that the determination is both repeatable (i.e., low scatter) and precise (i.e., with low systematic error). The marker should have a small pattern size but still be easily recognizable.

[0005] Fiducial markers can be classified according to the type of shape used to locate the reference point and the type of code used to determine the unique ID. The shape used to locate the reference point can be classified into circular, concentric rings, and line patterns. Fiducial marker codes can be classified into those based on patterns (arrangement of special features) and those based on barcodes (generally arranged in a circle, like the so-called "ring code"). Summary of the Invention

[0006] An object of the present invention is a method, a marker, a computer program, and a device. Other features and details of the present invention will be clear from the description and the drawings. The features and details described with respect to the method of the present invention are of course also applicable in relation to the marker of the present invention, the computer program of the present invention, and the device of the present invention, and vice versa, so these independent aspects of the present invention can be cross-referenced or always cross-referenced with respect to the disclosure.

[0007] In particular, the object of the present invention is a method for evaluating at least one marker for object metrological detection, especially object photogrammetry, on an (especially physical) object. The following steps are preferably computer-aided and / or automated:

[0008] - providing at least one rendering, especially mapping, of the marker, wherein each of the at least one rendering (such as as an image) is derived from sensor detection (such as image detection), and / or wherein the rendering can include, in particular, one or more image acquisitions of the object;

[0009] - determining a reference marker of the marker based on the provided rendering of the marker, wherein the reference marker preferably has a circular or annular or elliptical shape and / or has at least two partitions with different display attributes, especially color attributes such as color, intensity, saturation, etc., and wherein the partitions preferably each have the shape of a circular segment or an annular segment.

[0010] The reference marker determination may further include the following steps especially for evaluating markers for object metrological detection:

[0011] - in the provided rendering of the marker, transforming the color space and / or to one or more color spaces, especially transforming the mapping or rendering to one or more color spaces, so as to render the at least two partitions with different display attributes with substantially the same display attributes (such as brightness or color);

[0012] - identifying the reference marker based on the partitions displayed with substantially the same display attributes;

[0013] - providing a display (such as color space transformation) of the at least two partitions with different display attributes, preferably different colors or different brightnesses, especially by performing the inverse transformation according to the above transformation;

[0014] - identifying at least one reference point (especially the center) of the reference marker based on the provided display with different display attributes, especially by identifying the intersection of the partitions with different display attributes and preferably brightness in the display.

[0015] This has the advantage that the reference point can be reliably identified so as to use the reference for metrological detection of the object and / or to further evaluate (such as decode) the marker. Transforming to one or more color spaces when rendering the marker can also be understood as transforming the mapping or rendering to one or more color spaces. In this way, preferably, the rendering can be obtained in one or more transformed color spaces to obtain different visual displays of the rendering.

[0016] It may also be feasible that the recognition of the reference mark is carried out using a circle detector or an ellipse detector, and / or the recognition of the reference points of the reference mark, preferably the center, is carried out using, for example, an edge detector. By separating the channels, the edge detector can be used to accurately identify the center by finding the intersections of the partitioned or quarter circles.

[0017] Optionally, it may be provided that the determination of the reference mark includes the following steps:

[0018] - Using a shape recognition detector, especially a circle or ellipse, preferably an algorithm, to recognize the shape, especially a circle, in the provided mark rendering,

[0019] - Using different display attributes and preferably different colors, and preferably using a predetermined rationality criterion to check the rationality of the recognized shape,

[0020] - Based on the tested shape, recognizing one or more intersections of the partition to determine the reference point and / or preferably the center point as a result, where the determined results can be combined with each other.

[0021] This makes it possible to check the rationality of the recognized shape based on the knowledge of the display attributes used, so as to be able to more reliably determine the partition.

[0022] It may also be feasible to design the mark as a ring code mark, where the reference mark can be surrounded by a concentric ring or multiple ring segments forming a ring code. This allows further information to be obtained by evaluating the mark.

[0023] Within the scope of the present invention, it is also conceivable to provide the mark with an asymmetric mark element to indicate the start position for decoding the ring code. This can be, for example, an "asymmetric mark center", that is, an asymmetric mark point as a mark element. This provides additional information that can be used to distinguish different marks.

[0024] In another possible solution, it may be provided that the partition is designed as a quarter circle, where adjacent partitions are different in their display attributes, especially color.

[0025] It is also conceivable that the display can be color, where the reference mark has a concentric edge designed to have a color different from that of the partition or one of the many colors of the partition. This allows for better recognition of the reference mark and misrecognition when determining the reference point position.

[0026] Another object of the present invention is a marker, in particular a marker according to the present invention, which is used for attachment to (in particular physical) objects and for providing a reference point for metrological detection of at least one object. For this purpose, the marker may comprise a reference marker having at least two partitions with different display attributes. In this case, the display attributes of the partitions may show substantially no difference or a smaller difference when the reference marker is rendered in a transformed color space compared to when the reference marker is rendered in its primary color space or in terms of display attributes. The marker according to the present invention thus has the same advantages as those detailed with respect to the method of the present invention.

[0027] Another object of the present invention is a computer program, in particular a computer program product, which comprises instructions that cause a computer to perform the method according to the present invention when the computer program is run by the computer. The computer program according to the present invention thus has the same advantages as those detailed with respect to the method of the present invention.

[0028] Another object of the present invention is a data processing device configured to perform the method according to the present invention. The device may for example be a computer that runs the computer program according to the present invention. The computer may have at least one processor for running the computer program. A non-volatile data memory may also be provided, in which the computer program is stored and from which the processor can read the computer program for running.

[0029] Another object of the present invention may be a computer-readable storage medium that has the computer program according to the present invention / or comprises instructions that cause a computer to perform the method according to the present invention when run by the computer. The storage medium is for example configured as a data storage device such as a hard disk and / or a non-volatile memory and / or a memory card. The storage medium may for example be integrated into the computer.

[0030] In addition, the method of the present invention can also be designed as a computer-implemented method. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Other advantages, features and details of the present invention become clear from the following description, in which embodiments of the present invention are described in detail with reference to the figures. The features mentioned in the description may be important for the invention individually or in any combination. In the figures:

[0032] Figure 1 shows a schematic display of a method, device, storage medium and computer program according to an embodiment of the present invention,

[0033] Figures 2 to 4 shows schematic diagrams of various reference markers,

[0034] Figure 5 shows a diagram of the eccentricity of a circular projection,

[0035] Figure 6 Schematic diagram showing a marker according to an embodiment of the present invention,

[0036] Figure 7 Schematic display showing a transformation of a method according to an embodiment of the present invention, and

[0037] Figures 8 to 12 Other schematic diagrams showing markers according to an embodiment of the present invention. Detailed implementation manners

[0038] The most common reference markers use circles to locate reference points (such as the center of a circle). Circles are easy to identify at both large and small scales. For some examples, see Figure 2 . Instead of a single reference point, concentric rings can also be used to locate reference points (see also L. Calvet, P. Gurdjos, and V. Charvillat, "Camera tracking using concentric circle markers: Paradigms and algorithms", 19th IEEE International Conference on Image Processing, Orlando, Florida, USA, 2012, pp. 1361-1364, doi: 10.1109 / ICP.2012.6467121). Concentric rings can determine the marker plane and more accurately determine the marker center point (by extrapolating the change in the center point position as the circular contour shrinks). The reference point can also be represented by the intersection of lines or edges to obtain a clearly defined point, rather than relying on a circle with a blurred center point. These are not affected by (perspective) distortion because the intersection points are infinitesimal. For several other examples, see Figure 2 and Figure 3 . Examples of other fiducial markers can be found in Liu 2021.

[0039] Fiducial markers based on ring codes can also have a feature that serves as the marker center (usually a circle) surrounded by the code, usually as a ring code or codes of different thicknesses. The ring-coded markers according to Schneider 1993 (Optical 3-D-Measurement Systems for Quality Control in Industry. AICON-Industrial Photogrammetry and Image Processing, 1993) are probably the most commonly used photogrammetric markers.

[0040] Another important marker is the line pattern combined with the circular code, according to Bao 2017 ("A robust recognition and accurate locating method for circular coded diagonal target," Proceedings Volume 10458, AOPC 2017: 3D Measurement Technology for Intelligent Manufacturing; 104580Q(2017), https: / / doi.org / 10.1117 / 12.2283523). This marker combines the simple and robust decoding of the circular code and the high information content, while providing a well-defined center. For example, color-coded fiducial markers have also been used to identify markers at very different scales. The so-called pattern-based fiducial markers are based on a specific alignment of the pattern representing the fiducial marker code. A QR code is a simple example of this. Figure 4 Examples of fiducial markers with circles of different diameters and different colors are also shown, where the different colors are indicated by different hatching.

[0041] Each form for displaying the reference point has its advantages and disadvantages. A circle is the most easily recognizable target, but the center of the circle cannot be accurately located in a distorted image. A target with a line pattern is more difficult to recognize in an image, but the reference point is clearly defined. A concentric ring target is more easily recognizable to some extent (compared with a line pattern) and allows better center location (compared with a circular target), but the number of codes is limited.

[0042] A marker with a single circle in the center (which is usually ring-coded) is easily recognizable at different scales. However, if the marker is distorted or eccentric, the center cannot be accurately determined because the center of the 2D ellipse no longer matches the center of the 3D marker. This problem means that multiple images of the marker will result in different centers (random errors) and the center may also be incorrect in many measurement ranges according to (perspective) distortion (systematic errors caused by eccentricity). Figure 5 The eccentricity of the circular projection is shown, where the object plane 501 is projected onto the image plane 502 by perspective projection. C represents the reference point or center, C' represents the projection of C, and B' represents the center of the ellipse.

[0043] Random errors can be reduced by increasing the number of measurements, but this may not be feasible or may be too costly. Systematic errors cannot be reliably reduced. The diagonal pattern introduced by Bao 2017, rather than a circle, improves the reference positioning of the markers of the ring code. However, diagonal elements are more difficult to identify than circles, which eliminates an important advantage of the markers of Schneider 1993.

[0044] Markers with multiple concentric rings reduce the positional error of the reference points to some extent (compared to a circle), because the error can be extrapolated from different scales. However, concentric markers provide fewer possible IDs, require higher resolution or a larger image, and are more difficult to identify than ring code markers with a circle in the middle (see Figure 3 ).

[0045] Ring code markers can be mapped at different rotation angles. Therefore, it is not clear where the ring code starts, resulting in different possible code interpretations for a single coded marker. Therefore, the ring code may contain some form of redundancy to ensure rotational invariance. This redundancy reduces the number of available codes. A circle looks the same no matter how it is rotated, so it is not possible to determine how the marker is rotated. Therefore, it is not clear where the ring code around the marker starts, and the ring code on the marker may result in multiple IDs unless the number of codes is reduced to avoid ambiguity. Many ring code markers also result in valid but different codes when mirrored.

[0046] Figure 1 Schematically shown are a method 100, a device 10, a storage medium 15, and a computer program 20 according to an embodiment of the present invention. In particular, an improved marker is proposed. Specifically, the method 100 can be used to evaluate at least one marker 200 for metrological detection, and in particular photographic detection, of the physical object 50 on the object 50. According to a first method step 101, at least one rendering of the marker 200 can be provided first. For example, the at least one rendering can all be derived from sensor detection, where the rendering preferably can include one or more image acquisitions. According to a second method step 102, a reference marker 210 of the marker 200 can be determined based on the provided rendering of the marker 200. For example, the provided rendering is processed and evaluated in the form of a digital image. The shape of the reference marker 210 can be circular, annular, or elliptical. In particular, at least two partitions 220 have different display properties, such as different color properties such as color, intensity, saturation, etc., under at least one color space transformation. The partitions 220 can all have the shape of a circular segment or an annular segment.

[0047] According to an embodiment of the present invention, the determination 102 of the reference marker 210 includes the following steps:

[0048] - Transform the color space in the rendering of the marker 200 provided by the transformation 103 so as to display at least two partitions 220 having different display attributes with substantially the same display attributes such as brightness or color.

[0049] - Identify 104 the reference marker 210 based on the partitions 220 displayed with substantially the same display attributes.

[0050] - Provide 105 the display of at least two partitions 220 having different display attributes, preferably color or different brightness, in particular by performing an inverse transformation according to the transformation of 103.

[0051] - Identify 106 at least one reference point, preferably / for example the center, of the reference marker 210 based on the provided display with different display attributes, in particular by detecting the intersection points of the partitions 220 in the display with different display attributes, preferably brightness.

[0052] According to an embodiment of the present invention, a marker is proposed that can provide precise positioning even in an eccentric or distorted image. In a grayscale image (or in another suitable color space transformation 103), the marker can be backward compatible with software suitable for identifying ring-coded markers, in particular Schneider 1993, and accuracy may not be obtained. Since the positioning advantageously does not depend on the determination of the center of the ellipse, the size of the marker center can be increased to improve recognition without reducing accuracy. Since the rotational ambiguity is low, the number of codes can be increased.

[0053] Using a color with the marker allows more information to be provided, so the false positive risk is lower compared to other practices (candidates can be filtered out). In a grayscale image, the marker is as easy to see as a circle, but when separated by color channels, the center of the marker can be precisely positioned like a line pattern target.

[0054] Therefore, according to an embodiment of the present invention, a ring-coded marker 200 is provided, wherein the reference marker 201 in the form of a circle 210 is divided into partitions 220 of two different colors that ideally have the same brightness at the center of the ring-coded marker 200. In Figure 6 and Figures 8 to 12 , the different colors are represented by different hatching. For example, the different colors can be red 610 and blue 611.

[0055] In Figure 6In the illustrated embodiment, the partitions 220 of reference numeral 210, preferably quarter circles 220, are alternately formed in different colors (red 610 or blue 611) in a clockwise direction. In the grayscale image 601, the colors (ideally) have the same brightness, and the image looks like a black circle or a uniform gray circle, so a circle detector or an ellipse detector can be applied to the grayscale image. By separating the channels, an edge detector can be used to accurately detect the center by finding the intersections of the partitions 220 or the quarter circles 220.

[0056] Generally speaking, it may be a creative idea to use display attributes (such as colors 610, 611) with ideally equal brightness (or equal colors under any color transformation) to create a simple grayscale 601 (or transformed color space 601) shape that allows direct image processing. When viewing different color channels (or other color space transformations) 602, more complex shapes become visible, providing additional information (see Figure 6 ). In photogrammetry, this provides a win-win application scenario between simple or easily recognizable but inaccurate markers 200 and complex or difficult-to-recognize but information-rich and accurate markers 100.

[0057] According to an embodiment of the present invention Figure 6 The design of the illustrated marker 200 is an arrangement of four quarter circles 220, where adjacent quarter circles 220 can have different colors 610, 611 but approximately the same brightness. The marker 200 can be applied to the surface to be measured in various ways, such as by laser printing on an adhesive foil. The color of the marker 200 can have a different brightness from the background to obtain higher contrast.

[0058] The method according to an embodiment of the present invention may include the following steps for identifying and decoding a photogrammetric marker. First, according to the first step, an image can be taken with a digital camera or other sensor as a rendering of the marker, thus containing the proposed marker and preferably a fiducial marker. Subsequently, the image can be converted to grayscale, where initially only the brightness information can be considered. According to a further step, a suitable circle recognition algorithm can identify all the centers of the circles in the image. According to an optional step, the rationality of the identified circles can be checked based on color inspection and circles that do not have the expected color pattern can be discarded. In addition, the colors of the circles can be separated according to chromaticity (color), for example, by only considering the red channel. Then, an algorithm suitable for determining the center of the marker can be used to determine the intersection of the color gradients. In addition, these steps can be repeated in another color channel to find the center of the marker, and this result can be combined with the previous result. In this way, the recognition quality can be improved.

[0059] The decoding of the bar code can be simplified by aligning the bar code start point (or fixed offset) radially with respect to the edge of one of the middle quarter circles. In this way, there are only four (or two, for example if you have to start at the red-to-blue boundary) instead of eight starting positions (for a 14-bit code).

[0060] Different color separation schemes can be used, such as using only the red channel, only the blue channel, the hue in the HSV color model, or a combination of several, to distinguish different colors.

[0061] The center part does not have to have the same brightness, only different colors. These features can be resolved as a circle under any color transformation, rather than being resolved as a grayscale circle. For example, magenta and yellow with unequal brightness may be the two colors; before being recognized, magenta and yellow will be mapped to black and the image will be converted to grayscale; the previous magenta and yellow will now form a uniform black circle.

[0062] It can be conceived that if the brightness (or the display according to 103) is not exactly the same or due to color difference, the edge of the quarter circle 220 can be seen in the grayscale image 601 or another color channel image (see Figure 7 , where the red channel 701, the green channel 702, and the blue channel 703 are shown as examples here), which may result in lower accuracy of the contour-based circle detector. Therefore, according to an embodiment of the present invention, the boundary 801 of one of the two colors can be added to the reference mark 210, as Figure 8 shown.

[0063] Based on the idea of the previous paragraph, an edge ring 901 of different colors can also be used instead of the ring 801 of the same color around the center of the reference mark 210 (see Figure 9 ). This will be able to detect concentric rings on the grayscale image, and the advantage is that the false positive rate can be reduced at the beginning of the process because the rings are not common. In addition, the rationality check of the location can be performed by combining the concentric ring center method with the line intersection. In addition, the estimation of the mark orientation can lead to more degrees of freedom and achieve backward compatibility with other traditional marks.

[0064] The annular code 230 can also be filled with different colors so as to create an annular code when separated by color channels and create concentric rings in the grayscale image. This is illustrated in Figure 10 , where different colors are represented by different hatching lines. In this way, the advantages of the mark and the concentric circles can be combined and the annular code recognition can be improved because the annular code detector can be simply used in the grayscale image. The concentric rings can be used, for example, to determine more degrees of freedom than a single mark, which is an improvement over circular marks.

[0065] Any non-ordinary color in the code ring 230 (even a single color such as a red bar code on a white background) can improve anti-concealment, unless the concealed object is the same color as the code (the concealed object is usually black or silver). Another use of color is to ensure reflection invariance by creating an asymmetric marker 1101 using color. For example, it can be used to check Figure 11 whether the triangle in it points counterclockwise (this example also provides rotational invariance). In addition, the starting position 1102 of the ring code can be determined in this way.

[0066] Using more than two colors provides further advantages. Three colors reduce the possible starting positions of the circular code to a single starting position 1102 (see Figure 12 ), without the need to identify special geometric shape elements. In Figure 11 , the triangle can also be replaced with another color such as green; this will further simplify recognition, because the green triangle can be recognized based on color rather than shape, and then the intersection of the lines can be saved for recognition.

[0067] Instead of using an asymmetric circle, rotational invariance (without reducing the number of codes) can be obtained by starting the code ring 230 at the transition from one color to the next (such as from red to blue) in a specific direction and making the number of bits that the code ring 230 has not a multiple of four (generally speaking, the number of sectors in the center). The proposed idea also makes the marker insensitive to reflection. Using color in the reference marker allows reducing reflection on most colored reflective surfaces (such as car paint). The number of different colors and / or sectors in the center can be increased infinitely. In addition, in grayscale, the center can be an ellipse rather than a circle. Matching the apochromatic (or super-achromatic, etc.) characteristics of the lens with the marker color can allow (as much as possible) eliminating chromatic aberration. In this case, the light reflected by the marker is not the full spectrum, but has a specific wavelength, and the specific wavelength can be selected to match a wavelength at which the objective lens has the minimum chromatic aberration. The proposed marker 200 can also be used to calibrate sensors for autonomous vehicles.

[0068] The above description of the embodiments only exemplarily describes the present invention. Of course, without exceeding the scope of the present invention, the individual features of the embodiments can be freely combined with each other as long as this is technically advantageous.

[0069] This description also briefly refers to several sources, which are fully listed as follows:

[0070] Wong, 1998: WONG, Kam W.; LEW, Michael; WILEY, Anthony G. 3D metric vision for engineering construction. International Archives of Photogrammetry and Remote Sensing, 1988, Vol. 27, No. B5, pp. 647 - 656;

[0071] Ahn, 1997: 4th ABW Workshop Optische 3D-Formerfassung, TA Esslingen 22 - 23.01.1997 At: Esslingen, Germany;

[0072] Garrido-Jurado, 2014: https: / / doi.org / 10.1016 / j.patcog.2014.01.005;

[0073] Schneider, 1993: SCHNEIDER, Carl-Thomas; SINNREICH, Kurt. Optical 3-D measurement systems for quality control in industry. International Archives of Photogrammetry and Remote Sensing, 1993, Vol. 29, pp. 56 - 56, (isprs.org) (see also DE19733466B4);

[0074] Rice, 2006: https: / / doi.org / 10.1016 / j.pmcj.2006.07.006;

[0075] Bao, 2017: A robust recognition and accurate locating method for circular coded diagonal target (https: / / doi.org / 10.1117 / 12.2283523);

[0076] Yang, 2014: https: / / doi.org / 10.1016 / j.ijleo.2014.03.009;

[0077] Liu, 2021: A Novel Concentric Circular Coded Target, and Its Positioning and Identifying Method for Vision Measurement under Challenging Conditions, https: / / doi.org / 10.3390 / s21030855。

Claims

1. A method (100) for evaluating at least one marking (200) on a physical object (50) for metrological detection of the object (50), the method comprising the following steps: - providing (101) at least one rendering of the marking (200), wherein the at least one rendering is derived from a sensor detection, - determining (102) a reference marker (210) of the marker (200) based on the provided rendering of the marker (200), wherein the reference marker (210) has at least two partitions (220), the at least two partitions (220) having different display properties, The determination (102) of the reference marking (210) comprises the following steps for evaluating the marking (200) for metrological detection of the object (50): - transforming (103) into one or more color spaces of said rendering of said provided marking (200) so as to render said at least two partitions (220) having different display attributes with substantially the same said display attributes, - identifying (104) said reference marker (210) based on said partitions (220) being displayed with substantially the same said display attributes, - providing (105) a display of the at least two partitions (220) having different display properties, - identifying (106) at least one reference point of said reference marker (210) based on said display provided with different said display attributes.

2. The method (100) according to claim 1, characterized in that: The identification (104) of the reference mark (210) is performed using a circle detector or an ellipse detector, and the identification (106) of the reference point, preferably the center, of the reference mark (210) is performed, for example, using a gradient detector, an edge detector or a histogram method.

3. The method (100) according to any one of the preceding claims, characterized in that The determination (102) of the reference mark (210) comprises the following steps: - using a shape recognition algorithm, in particular a circle or an ellipse recognition algorithm, to recognize a shape, in particular a circle or an ellipse, in the provided rendering of the marking (200), - testing the plausibility of the identified said shape using different said display attributes and preferably different colors, - Based on the shape being tested, one or more intersection points of the partitions (220) are identified in order to determine the reference point and preferably the center point as a result, wherein the determined results are combined with one another.

4. The method (100) according to any one of the preceding claims, characterized in that The marking (200) is designed as a ring-coded marking (200), wherein the reference mark (210) is surrounded by ring segments or concentric rings forming a ring code (230).

5. The method (100) according to claim 4, characterized in that: An asymmetric marker element (1101) is set at the marker (200) to indicate a start position (1102) for decoding the circular code (230).

6. The method (100) according to any one of the preceding claims, characterized in that The subareas (220) are designed as quarter circles, and adjacent subareas (220) differ in their display properties, preferably in color.

7. The method (100) according to any one of the preceding claims, characterized in that The display attribute is color, wherein the reference mark (210) has concentric edges (801) designed to have a different color from the partition (220).

8. The method (100) according to any one of the preceding claims, characterized in that The mark (200) is designed as a ring-coded mark (200), wherein the color space of the provided rendering of the mark (200) is transformed according to a first transformation, thereby obtaining a continuous ring of the ring-coded mark (200), and the continuous ring is transformed according to a second transformation, thereby obtaining a decodable rendering of the ring-coded mark (200).

9. A marker (200) for attachment to a physical object (50) and providing at least one reference point for metrological detection of the object (50), the marker (200) comprising a reference marker (210), the reference marker (210) having at least two partitions (220) with different display attributes, wherein: The display properties of the partition (220) are substantially the same or have minor differences when the reference mark (210) is rendered in the transformed color space (601) compared to when the reference mark (210) is replicated in separate color channels and / or under any color space transform (602).

10. The marking (200) according to claim 9, characterized in that The marking (200) is used in a method (100) according to any one of claims 1 to 8 as at least one of the markings (200) evaluated.

11. A computer program (20), comprising instructions which, when the computer program (20) is run by a computer (10), cause the computer (10) to perform the method (100) according to any one of claims 1 to 8.

12. A data processing device (10) configured to perform the method (100) according to any one of claims 1 to 8.

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