STEREO CAMERA AND STEREOPHOTOGRAPHIC METHOD

Description

[0001] The present invention relates to a handheld device with a stereo camera and a method for image-based measurement of a remote object using such a device.

[0002] Devices and methods for stereophotogrammetric image acquisition are generally known in the prior art and are widely used to perform measurements in images, in particular to determine dimensions in an image, such as distances between depicted features.

[0003] For example, both EP 2 918 972 A2 and DE 10 2013 202 658 A1 disclose a method and a corresponding handheld device for creating a spatial model using stereoptometry. US 2016 / 037152 A1 and US 2010 / 074532 A1 disclose further methods and devices for generating 3D information and shapes from 2D images. A common method in stereo matching is the semi-global matching method. Christian Banz et al. present an architecture and implementation of the semi-global matching method in their paper "Real-Time Stereo Vision System using Semi-Global Matching Disparity Estimation: Architecture and FPGA-Implementation" (ISBN: 978-1-4244-7936-8, pages 93-101).

[0004] When using established stereophotogrammetry devices to capture images of artificial or man-made structures such as buildings, errors can occur during the automated matching process using feature extraction. This is because modern buildings, in particular, exhibit many uniform and repeating features. If the stereo base of the stereophotogrammetry device happens to be parallel to the direction of repetition during the capture, the identical features in the two images may be incorrectly matched, resulting in an incorrectly composited stereo image and flawed image measurements.

[0005] It is therefore an object of the present invention to provide a device and a method by which the probability of errors in assembling the images in the context of stereophotogrammetry can be reduced.

[0006] In particular, it is a task to provide such a device and such a method by which the probability of errors can be reduced without special design effort or significantly increased computing power.

[0007] Another task is to provide such a device and procedure that are easy and intuitive for a user to handle.

[0008] At least one of these problems is solved by implementing the characterizing features of the independent claims. Advantageous embodiments of the invention are found in the respective dependent claims.

[0009] Since contemporary buildings, in particular, are generally planned and constructed with straight lines and right angles, they are aligned with the direction of gravity and the horizon line orthogonal to it. This results in the directions of repetition of identical features (for example, the windows of a facade) being typically exactly horizontal and / or vertical. Therefore, in a stereo camera device according to the present invention, a stereo base is used that is arranged diagonally relative to a longitudinal axis of the device, which is essentially horizontally oriented during normal use.

[0010] A first aspect of the present invention relates to a handheld device for image-based measurement of a remote object, comprising a housing with a front and a back, a first camera and a second camera arranged on the back with a stereo base defined as a fixed distance from each other for capturing images of the object, an evaluation unit with an algorithm for stereophotogrammetric evaluation of the images from the first and second cameras, and a display unit arranged on the front for displaying images of the object and results of the stereophotogrammetric evaluation. The housing has a longitudinal axis, and the device is designed for handheld use by a user such that, for capturing images of the object, it is held with the longitudinal axis being substantially horizontal.The stereo base is diagonally aligned relative to the longitudinal axis, with the evaluation unit being designed to take into account the relative alignment of the stereo base during stereophotogrammetric evaluation, to recognize repeating patterns in at least one of the images and to derive a repetition direction of repeating features of the object, and to determine an angle β between the repetition direction and an epipolar line.

[0011] According to one embodiment, the device has an electronic distance meter, in particular designed as a laser distance meter, which is arranged on the back, for measuring a distance to the remote object, wherein the evaluation unit is designed to take the measured distance into account during stereophotogrammetric evaluation.

[0012] According to another embodiment of the device, the stereo base is arranged at an angle of at least 20° relative to the longitudinal axis, in particular at an angle between 30° and 60°.

[0013] According to one embodiment, the cameras are arranged such that the stereo base covers at least 75% of the maximum extent of the rear, in particular at least 90%.

[0014] In one embodiment, the device has input means arranged on the front for a user to input data and / or commands. The input means can be designed, in particular, as buttons, or the display unit and the input means can be configured as a touchscreen.

[0015] The input devices are specifically designed to allow a user to mark or select pixels in the object's image, where these pixels correspond to target points of the object. The evaluation unit can then be configured to determine the distance between the target points corresponding to the selected pixels and display it on the display unit.

[0016] In one embodiment, the device has an automatic recording functionality that runs after being triggered by a user, in which, in temporal proximity, in particular simultaneously, the first camera takes a first image and the second camera takes a second image of the object, the algorithm of the evaluation unit relates the first image and the second image to each other by means of feature recognition and on the basis of knowledge of the stereo base, and an image of the object is displayed on the display unit.

[0017] The process of relating the first image and the second image to each other can in particular involve rectifying the images and stereomatching the rectified images, especially using the semi-global matching method.

[0018] In one embodiment, the evaluation unit is configured to recognize repeating patterns in at least one of the images and to derive a repetition direction of repeating features of the object from this, and to determine an angle β between the repetition direction and an epipolar line, wherein the evaluation unit is configured to initiate measures when the value of the angle β falls below a predefined threshold, wherein the measures are suitable for leading to further recording of images of the object in which the predefined threshold is reached or exceeded.

[0019] According to one embodiment of the device, the measures include instructions for a user to hold the device at an angle for further recording compared to a previous recording, in particular wherein the instructions are displayed on the display unit.

[0020] A second aspect of the invention relates to a method for image-based measurement of a remote object using a handheld device according to the first aspect of the invention, comprising stereoscopic image acquisition by a first camera and a second camera, and stereophotogrammetric evaluation of the images from the first and second cameras. The device has a longitudinal axis and is held by a user during the acquisition such that the longitudinal axis is substantially horizontal. According to this aspect of the invention, the image evaluation is carried out taking into account a known angle α, wherein the first and second cameras are arranged on the device with a stereo base defined as a fixed distance from each other, such that the stereo base is diagonally aligned at the angle α relative to the longitudinal axis of the device.

[0021] According to one embodiment, the method comprises a display of an image on a display unit of the device, based on at least one of the images from the first camera and the second camera, a selection of dimensions to be measured by a user, a measurement corresponding to the selection based on the stereophotogrammetrically evaluated images, and an output of the result on a display unit and / or a storage of the result in a data memory of the device.

[0022] A third aspect of the invention relates to a computer program product with program code stored on a machine-readable medium for carrying out a method for image-based measurement of a remote object using a handheld device according to the second aspect, wherein the program is executed in an evaluation unit of a device according to the first or second aspect of the invention and comprises at least the following steps: a stereoscopic recording of images by the first camera and the second camera, and a stereophotogrammetric evaluation of the images of the first camera and the second camera, wherein the evaluation is carried out taking into account the known angle α.

[0023] A fourth aspect of the present invention relates to a system for image-based measurement of a remote object, comprising a handheld device and a computer program. The handheld device has a housing with a front and a back, a first and a second camera arranged on the back with a stereo base defined as a fixed distance from each other, for capturing images of the object, and a data interface for transmitting digital image data of captured images to an external electronic device.

[0024] The stereo base is diagonally aligned relative to the longitudinal axis, the program code containing information about the relative alignment of the stereo base, which can be executed by an external electronic device, and is designed to take the relative alignment of the stereo base into account during stereophotogrammetric evaluation.

[0025] According to one embodiment, the handheld device has the machine-readable carrier, in particular wherein the machine-readable carrier is a permanently installed data storage device, and is designed to transmit the program code to the external electronic device via the data interface.

[0026] The device and method according to the invention are described in more detail below by way of example, using specific embodiments schematically illustrated in the drawings, and further advantages of the invention are also discussed. Specifically, the drawings show: Fig. 1 a photograph of a building taken using a handheld stereophotogrammetry device of the prior art; Fig. 2a-b the stereophotogrammetry device made of Fig. 1 ; Fig. 3a-c Problems during the photogrammetric survey of the building with the device from Fig. 1Fig. 4a - an exemplary embodiment of a handheld stereophotogrammetry device according to the invention; Fig. 5 - a recording of an image of a building using an exemplary embodiment of a handheld stereophotogrammetry device according to the invention; Fig. 6a - a photogrammetric survey of the building with a device according to the invention; Fig. 7 - an exemplary embodiment of a method according to the invention for image-based surveying of a remote object; Fig. 8a - detection of an angle between an epipolar line and a repetition direction of features; Fig. 9 - method steps for detecting an angle between an epipolar line and a repetition direction; and Fig. 10 - an exemplary embodiment of a system according to the invention for image-based surveying of a remote object.

[0027] In Figure 1A photograph of a building 5 taken using a handheld stereophotogrammetry device 1 of the prior art is illustrated. The front side 11 of the device 1, facing the user during the photograph, is shown. This side has a display unit 20, for example designed as a touchscreen, and a panel with buttons 21 for selecting functions of the device 1.

[0028] On the rear side of the device 1, facing the building 5 to be recorded, two cameras 3a, 3b with a stereo base 30 are arranged. The stereo base 30 is parallel to a longitudinal axis of the device 1.

[0029] Building 5, the object to be recorded by cameras 3a and 3b, shown here against a horizon 6 for illustration, has a number of prominent features that are horizontally oriented, i.e., along the X-axis. This applies, for example, to the windows and the eaves, which are aligned along the horizontal lines 61-64. Furthermore, predominantly right angles are used, so the features of windows and walls also run vertically.

[0030] The stereophotogrammetry device 1 is designed such that it is preferably held upright by the user, i.e., with its longitudinal axis parallel to the horizon 6, partly because the measured values ​​displayed on the display unit 20 are easiest to read in this position. This results in the stereo base 30 running in the same direction as the prominent features of the building 5.

[0031] The stereophotogrammetry device 1 from Figure 1 is in the Figures 2a and 2bpresented in detail. Figure 2a the front 11 with display unit 20, and buttons 21, and Figure 2b the rear 12 with the two cameras 3a, 3b, which are arranged at the same height on the housing.

[0032] In the Figures 3a-c This illustrates the problems that arise when... Figure 1 shown image of building 5 using a device in the Figures 2a-b The device shown in 1 will occur.

[0033] Figure 3a Figure 51 and Figure 52 show side-by-side the images 51 and 52 of the building, which were simultaneously recorded by the two cameras 3a and 3b. Typical stereo matching algorithms, such as "Semi-Global Matching," require a prior step of rectifying the images relative to each other.

[0034] In Figure 3b has a corresponding rectification of the images from Figure 3aThe rectified images 51' and 52' show an epipolar line 70 that intersects them in a straight line. After rectification, the epipolar lines 70 in the rectified images 51' and 52' are horizontal, meaning that a pixel in the second image 52' corresponding to a pixel in the first image 51' lies on the same line. Similarly, a pixel 72 in the second image 52' corresponding to a point 71 in the first image 51' lying on the depicted epipolar line 70 can only lie on the epipolar line 70.

[0035] To match the two images 51 and 52, the algorithm must compare a feature in the first rectified image 51' only with those features in the second rectified image 52' that lie on the same epipolar line 70. Here, in the left image 51', a corner of a window mullion is shown as an example feature 71. Due to the uniform construction, similar features are repeated horizontally on the building – both windows are the same size and design and are also at the same height.

[0036] Since the epipolar line 70 also runs horizontally in the rectified images 51', 52', several similar or identical features 72, 72' lie next to each other on the epipolar line 70 in the right image 52'. This can lead to errors when matching the features if the algorithm mistakenly assigns a similar feature 72' to feature 71 in the first image 51 instead of the actually corresponding feature 72 in the second image 52.

[0037] Figure 3c Figure 51 shows rectified images 51' and 52', in which a distance measurement between two points is to be taken. In the left image 51', these are points 73 and 71, which each lie on a horizontal line of the building. Here, too, errors can occur due to the parallelism of the two epipolar lines 70' and 70' and the building features, resulting in an incorrect distance measurement.

[0038] In the Figures 4a and 4b An exemplary embodiment of a stereophotogrammetry device 1 according to the invention is shown. The rear side 12 of the housing 10 of the device 1 with the cameras 3a, 3b is shown in each case. Figure 4a Additionally, a laser distance meter 4 for measuring distances to a distant object (for example, to a point on a building) and a stop unit 17 for stopping the device 1 against a fixed surface are shown.

[0039] A distance measured with the laser distance meter 4 can be used in particular to scale the images taken by the cameras 3a, 3b, which increases the accuracy of photogrammetric measurements.

[0040] Figure 4b Figure 1 illustrates the geometry. It shows a longitudinal housing axis 15, a transverse housing axis 16 perpendicular to it, and the stereo base 30 diagonally oriented relative to both. Besides a longitudinal distance 33 running along or parallel to the longitudinal axis 15, the two cameras are also arranged with a transverse distance 35 perpendicular to the longitudinal axis 15. Depending on the longitudinal distance 33 and the transverse distance 35, this results in an angle α between the stereo base 30 and the longitudinal housing axis 15.

[0041] With the device 1 shown, even an inexperienced user can perform high-quality photogrammetric measurements on buildings and other man-made structures. It is generally not necessary to hold the device 1 at an angle during image acquisition. Furthermore, the angled arrangement of the cameras 3a,b advantageously allows for a maximum stereo base length 30.

[0042] However, the device must be tilted if natural or artificial objects are to be measured where object features are repeated at an angle corresponding to the inclination of the stereo base 30. Such cases are relatively rare in practice.

[0043] Figure 5 shows, analogous to Figure 1 , a recording of an image 50 of a building 5 using the handheld stereophotogrammetry device 1 of the Figures 4a and 4b Unlike the one in Figure 1In the device 1 shown, the stereo base 30 is not parallel to the horizontal lines 61-64 along which the prominent features of the building 5 are aligned, even though the device 1 is held upright.

[0044] The user can use cameras 3a, 3b to take stereoscopic pictures of building 5, and in an image displayed by the display unit 20, mark 50 pixels 56, 57 which correspond to target points 66, 67 on the real building 5, and determine and display a distance 68 between the target points photogrammetrically.

[0045] The Figures 6a-c illustrate how, by means of a device according to the invention, the substances in the Figures 3a-c The problems described can be avoided.

[0046] Figure 6a shows side by side the images from the two cameras 3a, 3b of the device. Figure 5Images 51 and 52 of the building were taken simultaneously. With typical stereo matching algorithms, such as "Semi-Global Matching", a prior step is required to rectify the images relative to each other.

[0047] In Figure 6b has a corresponding rectification of the images from Figure 6a The rectified images 51' and 52' show an epipolar line 70 that intersects them in a straight line. After rectification, the epipolar lines 70 in the rectified images 51' and 52' are horizontal, meaning that a pixel in the second image 52' corresponding to a pixel in the first image 51' lies on the same line. Similarly, a pixel 72 in the second image 52' corresponding to a point 71 in the first image 51' lying on the depicted epipolar line 70 can only lie on the epipolar line 70.

[0048] To match the two images 51 and 52, the algorithm must compare a feature in the first rectified image 51' only with those features in the second rectified image 52' that lie on the same epipolar line 70. Here, in the left image 51', a corner of a window mullion is shown as an example feature 71. Due to the uniform construction, similar features are repeated horizontally on the building – both windows are the same size and design and are also at the same height.

[0049] Due to the diagonal arrangement of the cameras, these horizontal lines appear diagonal in the rectified images. This results in a different appearance than in... Figure 3b In the right-hand image 52', there are not several similar or identical features next to each other on the epipolar line 70, but only feature 72, which corresponds to feature 71 in the first image 51. Errors in the assignment are thus avoided.

[0050] Figure 6c The image shows rectified images 51' and 52', in which a distance measurement of line 75 between two points is to be performed. In the left image 51', these are points 73 and 71, which each lie on a horizontal line of the building. Due to the diagonal arrangement of the cameras, these horizontal lines appear diagonal in the rectified images. Therefore, points 72 and 74 in the right image 52' can be clearly assigned to points 71 and 73 in the left image 51', thus allowing the distance of line 75 to be determined without error.

[0051] Alternatively, matching can of course also be performed without prior rectification. In the case of the conventional device made of Figure 1 The (nominally) horizontal epipolar line 70 then crosses several identical-looking horizontally arranged features 72 and 72'. With the device according to the invention made of Figure 5However, the epipolar line advantageously crosses only feature 72.

[0052] Alternatively, only specific points of interest can be related to each other, without having to process the entire image. For example, after the user has selected points of interest, a template matching process can be performed.

[0053] In Figure 7 An exemplary embodiment of a method 100 according to the invention for image-based measurement of a remote object using a handheld device according to the invention is illustrated.

[0054] In step 110, a stereoscopic image of the object is first taken using the two cameras. Optionally, a distance measurement 130 to the object can be performed simultaneously to accurately scale the images and thus have a precise scale for measurements within the image.

[0055] Using knowledge of the angle α (i.e., the relative orientation of the stereo base relative to the longitudinal axis of the device, see Figure 4b ), and optionally the distance measurement, a stereophotogrammetric evaluation of the stereoscopically recorded images takes place in step 140.

[0056] Simultaneously, in step 120, an image of the object is displayed to the user on the device's display unit. This could be, for example, one of the camera images or a stitched image. In step 150, the user then selects specific distances or areas from the image whose dimensions are to be measured. These dimensions are determined in step 160 by means of image measurement in the stereophotogrammetrically processed images and finally displayed to the user on the display unit in step 170. In step 180, the data is stored in the device's memory.

[0057] The device's evaluation unit is designed to recognize repeating patterns in the images and to derive a direction of repetition of recurring real-world features from them. This is done in the Figures 8a and 8b depicted.

[0058] Figure 8a shows, as an example, a rectified image 51' of the object as produced by the device in Figure 1 The algorithm of the evaluation unit recognizes the windows of the building as repeating features 77 and derives a repetition direction 78 of these features.

[0059] It is then determined that the repetition direction 78 lies parallel to the epipolar line 70, which, as in Figure 3bThis can lead to errors in image matching. In this case, the evaluation unit initiates measures to resolve this parallelism. These measures may include prompting the user to take a new picture, holding the device differently, particularly tilted compared to the last picture. This prompt is preferably displayed on the screen; additionally, an audible signal or vibration may also be triggered.

[0060] Figure 8b Figure 51' shows an example of a rectified image where the angle β between the repetition direction 78 of the features 77 and the epipolar line 70 is sufficiently large. This can be, in particular, the result of a change in the orientation of the device compared to that shown in Figure 51'. Figure 8a be - or the result of a recording with the device from Figure 5 .

[0061] The evaluation unit is designed to determine the angle β between the repetition direction 78 and the epipolar line 70, and to initiate measures when the value of the angle β falls below a predefined threshold.

[0062] Figure 9 illustrates further steps as part 200 of procedure 100 from Figure 7 , which relate to the in the Figures 8a,b The depicted alignment of epipolar line and repetition direction refers to this.

[0063] In particular, this procedural part 200 can be used in Figure 7The process begins in step 210 with an image acquisition using one or both cameras of the device, capturing at least one image of the object to be measured. Repeating object features are recognized as repeating patterns in the image (step 220) and compared with an epipolar line (step 230). The known angle α of the stereo base can be used for this purpose. If the direction of repetition and the epipolar line are too similar, i.e., if a value of the angle β is below a defined threshold, an instruction is issued to the user to change the position of the device (step 240). Otherwise, the process can continue as described in [step 220]. Figure 7 The procedures shown will be carried out.

[0064] Figure 10Figure 1 shows another exemplary embodiment of a handheld stereophotogrammetry device 1 according to the invention. This device has at least one interface 90, 95 for connection to an external electronic device, for example a laptop computer 2.

[0065] As examples, a connector interface 90 for establishing a wired connection 92 (e.g., via USB) and a radio interface 95 for establishing a wireless connection 97 (e.g., via WLAN or Bluetooth) are shown. Image data from the images captured by cameras 3a, 3b are transmitted via the (wired or wireless) connection 92, 97 to laptop 2, where they are evaluated stereophotogrammetrically. The system includes corresponding software, which also provides information about the arrangement of the two cameras 3a, 3b, and is installed on laptop 2. The software is preferably stored in a memory unit 19 of the device 1 and is transmitted to laptop 2 via the (wired or wireless) connection 92, 97. It can also be provided on a data carrier or in the cloud.The advantage of this embodiment is that the handheld device 1 does not need its own evaluation unit; a display unit is also unnecessary. As a result, the device 1 can be more compact and lighter and manufactured with less technical effort.

[0066] The stereophotogrammetry device 1 is used by the user to capture images, the data from which are transmitted to the laptop 2, either in real time or following a series of images. The software is stored in the memory unit 19 and is sent to the laptop 2, for example, together with the image data. Steps 140-170 of procedure 100 can then be performed on the laptop. Figure 7 be feasible.

[0067] It is understood that these figures only schematically represent possible embodiments. The various approaches can be combined with each other as well as with prior art methods and equipment.

Claims

1. Handheld device (1) for the image-based measurement of a remote object (5), comprising - a housing (10) having a front side (11) and a rear side (12); - a first camera (3a) and a second camera (3b), which are arranged having a stereo base (30) as a fixed spacing in relation to one another on the rear side (12), for recording images (51, 52) of the object (5); - an analysis unit having an algorithm for the stereophotogrammetric analysis of the images (51, 52) of the first camera (3a) and the second camera (3b); and - a display unit (20), which is arranged on the front side (11), for displaying images (50) of the object (5) and results of the stereophotogrammetric analysis; wherein the housing (10) has a longitudinal axis (15) and the device (1) is designed for handheld use by a user in such a way that the device (1) is held to record images (51, 52) of the object (5) in such a way that the longitudinal axis (15) is substantially horizontal, characterized in that, the stereo base (30) is aligned diagonally in relation to the longitudinal axis (15), wherein the analysis unit is designed for the purpose of - taking into consideration the relative alignment of the stereo base (30) during the stereophotogrammetric analysis, - recognizing repeating patterns in at least one of the images (51, 52) and deriving a repetition direction (78) of repeating features (77) of the object (5) therefrom, and - ascertaining an angle β between the repetition direction (78) and an epipolar line (70).

2. Device (1) according to Claim 1, characterized by an electronic distance meter (4), designed in particular as a laser distance meter, which is arranged on the rear side (12), for measuring a distance to the remote object (5), wherein the analysis unit is designed for the purpose of taking into consideration the measured distance during the stereophotogrammetric analysis.

3. Device (1) according to Claim 1 or Claim 2, characterized in that the stereo base (30) is arranged at an angle (α) of at least 20°, in particular at an angle between 30° and 60°, in relation to the longitudinal axis (15).

4. Device (1) according to any one of the preceding claims, characterized in that the cameras (3a, 3b) are arranged such that the stereo base (30) comprises at least 75% of a maximum extension of the rear side (12), in particular at least 90%.

5. Device (1) according to any one of the preceding claims, characterized by input means, which are arranged on the front side (11), for the input of data and / or commands by a user, in particular wherein the input means are embodied as buttons (21), or wherein the display unit (20) and the input means are designed as a touchscreen.

6. Device (1) according to Claim 5, characterized in that the input means are designed for the purpose of enabling marking or selection of pixels (56, 57) in the image (50) of the object (5) by a user, wherein the pixels (56, 57) correspond to target points (66, 67) of the object (5), and the analysis unit is designed for the purpose of ascertaining a distance (68) between the target points (66, 67) corresponding to the selected pixels (56, 57) and displaying it on the display unit (20).

7. Device (1) according to any one of the preceding claims, characterized by a recording functionality running automatically after triggering by a user, in the scope of which - in chronological correlation, in particular simultaneously, the first camera (3a) records a first image (51) and the second camera (3b) records a second image (52) of the object (5), - the algorithm of the analysis unit relates the first image (51) and the second image (52) to one another by means of feature recognition and on the basis of the knowledge about the stereo base (30), and - an image (50) of the object (5) is displayed on the display unit (20), in particular wherein the relating of the first image (51) and the second image (52) to one another comprises: - a rectification of the images (51, 52), and - a stereo matching of the rectified images (51', 52'), in particular by means of the semi-global matching method.

8. Device (1) according to claim 1, characterized in that the analysis unit is designed for the purpose - of recognizing repeating patterns in at least one of the images (51, 52) and deriving a repetition direction (78) of repeating features (77) of the object (5) therefrom, and - of ascertaining an angle β between the repetition direction (78) and an epipolar line (70), wherein the analysis unit is designed for the purpose of initiating measures if the value of the angle β falls below a predefined threshold value, wherein the measures are capable of resulting in a further recording of images (51, 52) of the object (5), in which the predefined threshold value is reached or exceeded.

9. Device (1) according to claim 8, characterized in that the measures comprise a handling instruction for a user to hold the device (1) diagonally for the further recording in comparison to a prior recording, in particular wherein the handling instruction is displayed on the display unit (20).

10. Method (100) for the image-based measurement of a remote object (5) by means of a handheld device (1) according to any one of the preceding claims, comprising - a stereoscopic recording (110) of images (51, 52) by a first camera (3a) and a second camera (3b), and - a stereophotogrammetric analysis (140) of the images (51, 52) of the first camera (3a) and the second camera (3b), wherein the device (1) has a longitudinal axis (15) and is held by a user during recording in such a way that the longitudinal axis (15) is substantially horizontal, characterized in that - the analysis (140) of the images (51, 52) is performed in consideration of a known angle α, wherein the first camera (3a) and the second camera (3b) are arranged having a stereo base (30) as a fixed spacing in relation to one another on the device (1) such that the stereo base (30) is diagonally oriented at the angle α in relation to a longitudinal axis (15) of the device (1), - in at least one of the images (51, 52) repeating patterns are recognized and a repetition direction (78) of repeating features (77) of the object (5) is derived therefrom, and - an angle β between the repetition direction (78) and an epipolar line (70) is ascertained.

11. Method (100) according to Claim 10, characterized by - a display (120) of an image (50) on a display unit (20) of the device (1), based on at least one of the images (51, 52) of the first camera (3a) and the second camera (3b), - a selection (150), by a user, of dimensions to be measured, - a measurement (160) corresponding to the selection (150) based on the stereophotogrammetrically analyzed images (51, 52), and - an output (170) of the result on a display unit (20) and / or a storage (180) of the result in a data storage unit of the device (1).

12. Computer program product having program code which is stored on a machine-readable carrier for executing a method (100) according to Claim 10 and in particular according to Claim 11, for the image-based measurement of a remote object (5) by means of a handheld device (1), wherein the program is executed in the analysis unit of the device (1) according to any one of Claims 1 to 9 and at least comprises the following steps: - a stereoscopic recording (110) of images (51, 52) by the first camera (3a) and the second camera (3b), and - a stereophotogrammetric analysis (140) of the images (51, 52) of the first camera (3a) and the second camera (3b), wherein the analysis (140) is performed in consideration of a known angle α, - a recognition of repeating patterns in at least one of the images (51, 52) and deriving a repetition direction (78) of repeating features (77) of the object (5) therefrom, wherein - an ascertainment of an angle β between the repetition direction (78) and an epipolar line (70).

13. System for the image-based measurement of a remote object (5), comprising a handheld device (1) and a computer program product, wherein the handheld device (1) comprises: - a housing (10) having a front side (11) and a rear side (12); - a first camera (3a) and a second camera (3b), which are arranged having a stereo base (30) as a fixed spacing in relation to one another on the rear side (12), for recording images (51, 52) of the object (5); and - a data interface (90, 95) for transmitting digital image data of recorded images (51, 52) to an external electronic device (2), wherein the housing (10) has a longitudinal axis (15) and the device (1) is designed for handheld use by a user in such a way that the device (1) is held to record images (51, 52) of the object (5) in such a way that the longitudinal axis (15) is substantially horizontal, and wherein the computer program product comprises program code which is stored on a machine-readable carrier having an algorithm for the stereophotogrammetric analysis of the images (51, 52) of the first camera (3a) and the second camera (3b), characterized in that the stereo base (30) is aligned diagonally in relation to the longitudinal axis (15), wherein the program code - contains an item of information about the relative alignment of the stereo base (30), - is executable in the external electronic device (2), and is designed for the purpose of - taking into consideration the relative alignment of the stereo base (30) during the stereophotogrammetric analysis, - recognizing repeating patterns in at least one of the images (51, 52) and deriving a repetition direction (78) of repeating features (77) of the object (5) therefrom, and - ascertaining an angle β between the repetition direction (78) and an epipolar line (70).

14. System according to Claim 13, characterized in that the handheld device (1) - comprises the machine-readable carrier, in particular wherein the machine-readable carrier is a permanently installed data storage unit (19), and - is designed for the purpose of transmitting the program code via the data interface (90, 95) to the external electronic device (2).