Scanning surveying system

A scanning surveying system comprises a base 5, an alidade 3 mounted on the base, a first motor 6 to rotate the alidade about a first axis 9, a rotating mirror 21 rotatable about a second axis 16, a second motor 23 to rotate the mirror. An optical distance measuring unit 11 is configured to direct measuring light onto the rotating mirror such that it is reflected towards objects and to receive measuring light back from these objects via the rotating mirror. The system further comprises a camera 81 and a controller for controlling the first motor based on the images recorded by the camera such that the measuring light is reflected from the rotating mirror in a direction corresponding to a selected location within the image.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to European Patent Application No. EP20180273.3, filed Jun. 16, 2020, the contents of which are incorporated herein by reference in their entirety for all purposes.

FIELD OF INVENTION

The present invention relates to scanning surveying systems having rotating mirrors.

BACKGROUND

A conventional scanning surveying system comprises an optical distance measuring unit generating a beam of measuring light which can be directed to an object. The object reflects or scatters some of the incident measuring light such that the optical distance measuring unit receives measuring light back from the object. The optical distance measuring unit may then determine the distance of the object from the optical distance measuring unit based on, for example, a time-of-flight analysis.

The scanning surveying system further comprises a rotating mirror, wherein the optical distance measuring unit directs the generated beam of measuring light onto the rotating mirror from which the beam is reflected to objects surrounding the scanning surveying system depending on the rotational position of the rotating mirror.

The optical distance measuring unit and the rotating mirror are typically mounted on an alidade which is rotatable relative to a tripod about a vertical axis, and the rotating mirror is typically rotatable about a horizontal axis. By driving the alidade about the vertical axis over a range of 180° at a relatively low speed, driving the rotating mirror at a high speed and performing distance measurements at a very high frequency, it is possible to record distance measurements against a great number of surface points of substantially all objects surrounding the scanning surveying system. The ensemble of measurement data resulting from such scan is referred to as a point cloud in the art. The accuracy of the geometry information relating to the surrounding objects increases with the number of measurements performed per scan. Conventional scanning surveying systems can perform more than one million distance measurements per second so that a scan providing a desirable accuracy can be completed in a few minutes.

It is apparent that the amount of data generated during such scan can be huge. Typically, the point clouds recorded by a scanning surveying system during an excursion are transferred to a powerful computer for off-line processing. With such off-line processing, the recording and the analyzing of the data fall apart and, for example, the surveying engineer making the scan of a site will typically no longer stay at that site when the processing of the recorded data has been completed. If an analysis of the recorded data reveals that some information is missing from the data or that some portions are inaccurate, the scan has to be repeated in an additional excursion of the surveying engineer. It is apparent that the utilizability of high performant scanning surveying systems can still be improved.

Accordingly, it is an object of the present invention to provide a scanning surveying system offering a broader range of applications.

SUMMARY

According to embodiments of the present invention, a scanning surveying system comprises a base, an alidade mounted on the base such that it is rotatable relative to the base about a first axis, a first motor configured to rotate the alidade relative to the base, a rotating mirror mounted on the alidade and rotatable relative to the alidade about a second axis, a second motor configured to rotate the rotating mirror relative to the alidade, and an optical distance measuring unit configured to direct measuring light onto the rotating mirror such that it is reflected towards objects surrounding the scanning surveying system, and to receive measuring light back from these objects via the rotating mirror.

The base can be provided by a tripod, for example. Other configurations for mounting the alidade are possible, however. In some embodiments, it is possible to orient the base such that the first axis is oriented in the vertical direction, i.e. parallel to the direction of gravity at a given measuring site. The second axis can be oriented orthogonal to the first axis. This is not a requirement, however. The optical distance measuring unit is configured to output data representing the distance from the optical distance measuring unit of the object from which the emitted measuring light is received back. For example, the optical distance measuring unit may use a time-of-flight method such that the data representing the distance is determined based on a time difference between the time of emission of a pulse of measuring light from the optical distance measuring unit and a time of receipt by the optical distance measuring unit of measuring light from an object corresponding to the emitted pulse. Other distance measuring techniques, such as phase shift measurements and combinations of time-of-flight and phase shift measurements, can be used by the optical distance measuring unit as well.

According to some embodiments, the scanning surveying system comprises at least one camera configured to record at least one image. The at least one camera can be mounted on the alidade. Herein, the at least one camera can be mounted directly on the alidade, i.e. on a component which is rigidly connected with the alidade, or it can be indirectly mounted on the alidade, i.e. it can be mounted on a component which is itself mounted on the alidade to be movable or rotatable relative to the alidade. However, the mounting of the at least one camera on the alidade results in a rotation of the alidade relative to the base about the first axis results in a corresponding rotation of the at least one camera relative to the base about the first axis.

The camera can be an optical camera detecting visible light such that the camera detects a visible-light image of objects surrounding the scanning surveying system. The camera may also detect light of other spectral ranges then visible light in order to record infrared-light or near-infrared-light images of the objects surrounding the scanning surveying system. The at least one camera may have a two-dimensional image sensor for detecting the image. The two-dimensional image sensor is configured to determine data representing a location in the coordinate system of the image sensor where detected light was incident on the image sensor. The two-dimensional image sensor may include a plurality of pixels. The pixels are detector elements within the two-dimensional image sensor which are configured to detect light which is incident on the detector. The pixels may be arranged in a regular two-dimensional array pattern, for example.

According to some embodiments, the scanning surveying system comprises a controller configured to control the first motor based on the at least one recorded image such that the measuring light is reflected from the rotating mirror in a direction corresponding to a selected location within the image. Herein, the at least one camera can record further, additional images while the controller performs its control of the first motor, and the controller can be configured to control the first motor based on these further additional recorded images which are then used as “live images” to perform accurate control of the first motor.

According to some embodiments, the scanning surveying system comprises a user interface including a display configured to display a representation of the at least one image recorded by the at least one camera to a user, and to receive position data representing the selected location within the recorded image.

The user interface can be of any type allowing interaction of the scanning surveying system and a human user thereof. The display of the user interface can be configured to display information to the user. The display may include displays such as a computer screen, the display of a mobile device, such as a tablet computer or telephone, a head mounted display and other display configurations. The display may include a liquid crystal display, a light-emitting diode display, such as an OLED, AMOLED, QD-LED, and other suitable types.

The position data received by the user interface from the user represents a location within the recorded image. The location may be represented as coordinates of a given pixel in the recorded image in a suitably selected coordinate system of the image, for example.

The user interface can be configured to receive the position data in various ways. For example, the user interface may include a keyboard for the user to enter coordinates representing the position of a selected pixel. Moreover, the user interface may display a cursor, pointer or other indicator representing the selected position on the display itself. The user may move the selected position around on the display by hitting keys of the keyboard or operating a mouse, for example. Moreover, the display may be configured to be touch-sensitive and to detect touch events on the display. For example, coordinates of a position on the touch screen where the touch event was detected can be transformed to coordinates in the coordinate system of the touch screen or the detected image.

According to some embodiments, the at least one camera can be configured to record a still image in response to a user input, and to display the recorded still image on the display. According to other embodiments, the at least one camera is configured to record a sequence of images, and the user interface is configured to display representations of the sequence of images. This may include configurations where live videos recorded by the camera are displayed on the display.

Therefore, the user may identify an object of interest within the image displayed on the display and select the location on the display where the object of interest is displayed. When the user has selected a location within the image, the controller may start to operate the first motor such that the alidade is rotated about the first axis until the beam of measuring light can be directed to the object selected by the user on the display. A distance measurement can then be performed when the beam of measuring light is directed onto the object in order to determine the distance of the object selected by the user from the scanning surveying system.

According to some embodiments, the controller is configured to search the at least one image for a representation of a predefined pattern and to use a position of the searched representation of the predefined pattern within the image as the selected location within the image.

The predefined pattern in the image can be a predefined pattern of a predefined object placed in the surroundings of the scanning surveying system. The predefined object may include a marker applied to an object located in the surroundings of the scanning surveying system. The marker can be applied to the object by an adhesive or other means. The marker provides a pattern which can be identified in the image if the object to which the marker is applied appears in the image. The marker may include patterns, such as a cross, a circle, lines, checkerboard patterns or the like. The controller is configured to recognize the predefined pattern in the recorded image also when the predefined pattern is not orthogonally arranged relative to the scanning distance measuring system by taking a range of possible orientations of the predefined pattern relative to the scanning distance measuring system into account.

Such predefined patterns may indicate reference positions on walls of buildings, for example. Moreover, such predefined pattern can be mounted on a rod, wherein the rod can be carried by a user, and the user may place the tip of the rod on a position of the floor such that the scanning surveying system may measure the distance between the position on the floor and the scanning surveying system when the orientation of the rod relative to the floor and the distance between the predefined pattern and the tip of the rod are known.

According to some embodiments, the controller is configured to record a distance measurement when the measuring light is reflected from the rotating mirror in the direction corresponding to the selected location within the image. The optical distance measuring unit may be configured to generate at least one pulse of the measuring light and to perform a distance measuring using this pulse of the measuring light. In some embodiments herein, the controller is configured to control the second motor such that it rotates continuously at constant speed, and to trigger the generation of the pulse of the measuring light based on the selected location within the recorded image. The controller may then calculate a suitable time for the generation of the pulse of measuring light such that it is directed to the selected object based on the rotation of the rotating mirror at the constant speed. The controller may then trigger the generation of the pulse such that the pulse is emitted at the determined time.

According to other embodiments, the optical distance measuring unit is configured to generate a sequence of pulses of the measuring light and to perform a corresponding sequence of distance measurements using these pulses of measuring light. The sequence of pulses can be generated at a constant rate, for example.

According to some embodiments herein, the controller is configured to control the second motor such that it rotates at a constant rate, and to control a phase of the rotation of the second motor relative to the sequence of the pulses of the measuring light based on the selected location within the recorded image. By controlling such phase, it is possible to direct at least one pulse of measuring light to the selected object, assuming that the speed of the rotating mirror is constant and the rate of the generation of the pulses is constant. Since plural distance measurements are performed during one rotation of the rotating mirror, the controller may then select one or more distance measurements among the plural distance measurements. The selected one or more distance measurements can be the distance measurement corresponding to the pulse directed to the object of interest.

According to some embodiments, the scanning surveying system comprises a mounting structure mounted on the alidade and rotatable relative to the alidade about a third axis, wherein a third motor can be provided to rotate the mounting structure about the third axis. The third axis may substantially coincide with the second axis. According to some embodiments, the at least one camera is mounted on the mounting structure. The controller can be configured to control the third motor in order rotate the mounting structure about the third axis such that the at least one camera can be oriented in various directions about the second axis. The third motor can be operated in situations when an object of interest is not in the field of view of the at least one camera. The mounting structure can then be rotated until the object of interest appears within the field of view of the at least one camera and is displayed on the display.

According to some embodiments, the rotating mirror is mounted on the mounting structure. The rotation of the mounting structure can then be used to adjust the phase of the rotating mirror relative to the pulses generated by the optical distance measuring unit.

According to exemplary embodiments, the scanning surveying system comprises a detector mounted on the alidade such that it can receive measuring light when the rotating mirror is in a predetermined range of rotational positions. The controller is configured to determine locations of incidence of light pulses generated by the optical distance measuring unit on the detector. As illustrated above, each distance measurement is performed in a direction determined by the rotational position of the rotating mirror when the pulse of measuring light is emitted. By determining a location of incidence of a light pulse generated by the optical distance measuring unit at a given time when the rotating mirror is within the range of rotational positions it is possible to determine the dependency between the measuring directions, emission times of the pulses of measuring light and the rotational positions of the rotating mirror. According to exemplary embodiments, the controller is configured to determine locations of incidence of light pulses generated by the optical distance measuring unit on the detector, to trigger a generation of light pulses by the optical distance measuring unit based on the determined locations when performing distance measurements and/or to control the second motor based on the determined locations when performing distance measurements.

Accordingly an embodiment of the invention includes a method of operating a scanning surveying system, wherein the scanning surveying system comprises a base, an alidade mounted on the base and rotatable relative to the base about a first axis, a first motor configured to rotate the alidade relative to the base, a rotating mirror mounted on the alidade and rotatable relative to the alidade about a second axis, a second motor configured to rotate the rotating mirror relative to the alidade, an optical distance measuring unit configured to direct measuring light onto the rotating mirror such that it is reflected towards objects surrounding the scanning surveying system, and to receive measuring light back from these objects via the rotating mirror, and a detector mounted on the alidade to receive measuring light when the rotating mirror is in a predetermined range of rotational positions. The method comprises determining locations of incidence of light pulses generated by the optical distance measuring unit on the detector, triggering a generation of light pulses by the optical distance measuring unit based on the determined locations when performing distance measurements; and/or controlling the second motor based on the determined locations when performing distance measurements.

DETAILED DESCRIPTION

Exemplary scanning surveying systems will be illustrated with reference toFIGS.1to3below.FIG.1is a simplified sectional view schematically illustrating details of a scanning surveying system.

The scanning surveying system1comprises a base3mounted on a tripod5, and an alidade7. The alidade7is mounted on the base3and can be rotated relative to the base3about an axis9as indicated by an arrow10inFIG.1. The tripod5can be adjusted such that the axis9is oriented in the vertical direction when the surveying system1is used. A motor6is provided to rotate the alidade7relative to the base3. The motor6is controlled by a controller19mounted within the base3, or on any other suitable component of the surveying system1. The surveying system1may further comprise a rotational encoder (not shown inFIG.1) connected to the controller19so that the controller19can measure the current rotational position of the alidade7relative to the base3.

The surveying system1further comprises an optical distance measuring unit11mounted on a mounting structure13. The mounting structure13is mounted on the alidade7and rotatable relative to the alidade7about an axis14as indicated by an arrow15inFIG.1. The axis14is substantially orthogonal to the axis9of rotation of the alidade7relative to the base3. A motor17is provided to rotate the mounting structure13relative to the alidade7. The motor17is controlled by the controller19. Moreover, the surveying system1may comprise a rotational encoder (not shown inFIG.1) connected to the controller19so that the controller19can measure the current rotational position of the mounting structure13relative to the alidade7.

The optical distance measuring unit11comprises a rotating mirror21carried by a motor23mounted on the mounting structure13. The motor23is controlled by the controller19and rotates the rotating mirror21about an axis16of rotation as indicated by an arrow18inFIG.1. The axis16of rotation of the mirror substantially coincides with the axis14of rotation of the mounting structure13relative to the alidade7. The rotating mirror21has a substantially flat mirror surface25having a surface normal oriented at an angle of 45 degrees relative to the axis16of rotation of the rotating mirror21.

The measuring unit11further comprises a light source27, such as a laser source, pulsed laser source and/or a fiber laser, for example. The light source27is mounted on the mounting structure13and configured to generate light pulses which are supplied to an emitting element29, such as a collimation lens, via a fiber31. A thin beam33of measuring light is emitted from the emitting element29, enters a glass prism35and is reflected from an internal surface37of the prism35such that it substantially coincides with the axis16of rotation of the rotating mirror21. The beam33of measuring light leaves the prism35through a glass plate39. The glass plate39has a mirror surface41having a surface normal which can be oriented relative to the axis16of rotation of the rotating mirror21at an angle of 45 degrees, for example. The mirror surface41has a central portion43traversed by the beam33of measuring light. The central portion43may carry an antireflective coating such that a low amount of the measuring light is reflected from the mirror surface41while the main portion of the beam33of measuring light is incident on the mirror surface25at an angle of 45 degrees. When the rotating mirror21is oriented as shown inFIG.1, the beam33of measuring light is reflected from the mirror surface25such that the thin beam33of measuring light is emitted from the surveying system1in the vertical direction as indicated by an arrow45inFIG.1. This measuring light will be incident on an object, and a portion of that light is scattered by the object or reflected from the object such that it travels back to the surveying system1as a broader beam46as indicated by arrows47inFIG.1.

The mounting structure13comprises one or more windows49allowing the beam33of measuring light to leave the measuring unit11and the light47received back from the object to enter the measuring unit11. The window49can be a single ring-shaped window extending around the axis18of rotation of the rotating mirror21.

The light received back from the object is incident on the mirror surface25of the rotating mirror21, and is reflected from the mirror surface25to be incident on the mirror41. Apart from its central portion43, the mirror surface41carries a reflective coating such that most of the light received back from the object is directed towards a focusing lens51concentrating the light received back from the object onto a detector53. Detection signals produced by the detector53are supplied to the controller19. The controller19may measure differences between times when light pulses are generated by the light source27and corresponding times when these light pulses are detected by the detector53. These time differences represent the time of flight of a light pulse from the measuring unit to the object and from the object back to the measuring unit11. This measured time of flight is indicative of the distance of the object from the surveying system1.

The controller19may control the motor23to rotate the mirror21about the axis16. This results in the light beam45emitted from the surveying system1to rotate about the axis16in a plane orthogonal to the axis16. By operating the motor6in order to rotate the alidade7about the axis9, the controller19may direct the measuring light beam45emitted from the surveying system1in any direction.

The scanning surveying system1further comprises a calibration unit55configured to determine properties of the scanning surveying system1. Details of a calibration unit suitable for integration in the scanning surveying system1are illustrated in the co-pending European patent applications of the present applicant with application numbers 19 157 547.1 and 19 157 555.4 filed on Feb. 2, 2019, wherein the whole disclosure of these patent applications is incorporated herein by reference.

The alidade7includes a window59and a hollow shaft61such that the light beam45may enter the calibration unit55, and that calibration light generated by the calibration unit55can be directed on components mounted on the alidade7.

The surveying system1further comprises plural cameras81mounted on the mounting structure13. Each camera81comprises an objective lens83and a position sensitive detector85and is configured to record visual images of the surroundings of the surveying system1. Each camera81has a main axis87defined by the optical axis of the objective lens83. The plural cameras81differ with respect to the orientations of their main axes87relative to the mounting structure13. The main axes87of the plural cameras81differ with respect to their orientation in the circumferential direction about the axis14and with respect to the azimuthal direction with respect to the axis14. The cameras81can be used to record visual light images of the surroundings of the surveying system simultaneously with the recording of distance measurements using the measuring light beam45reflected from the rotating mirror21, for example.

The scanning surveying system1further comprises a graphical user interface63formed by a tablet computer64having a touch scream65in the illustrated embodiment.

The cameras81are connected to the controller19by a wireless or a wire-based data connection. The controller19is configured to obtain image data representing the images recorded by the cameras81from the cameras81. The controller19may process the image data using suitable image processing algorithms. For example, the controller19may process the images in order to adjust brightness and contrast and to change the image resolution or number of pixels per image.

The controller19is further configured to display the images recorded by the cameras81on the touch screen65by sending the image data to the graphical user interface63.

FIG.2shows an exemplary image displayed on the touch screen65of the scanning surveying system1according to a specific example. The image has been recorded by one of the cameras81and contains objects in the surroundings of the scanning surveying system1, such as a table, cabinets, a door, and floor, side walls and ceiling of a laboratory room.

Reference numeral67inFIG.2indicates a dotted line, wherein each dot represents a direction in which a distance measurement can be obtained by the scanning surveying system1when the alidade7is in the rotational position about the vertical axis9where the image was recorded by the camera81. The dots of the line67lie on a plane orthogonal to the axis14. However, due to the image distortion of the camera81, the dots of the line67appear to lie on a curved line. The dots of the line67are spaced apart from each other by a distance defined by the repetition rate of the generation of pulses emitted by the distance measuring unit11and the rotational speed of the rotating mirror21.

FIG.2further shows a pen tool69displayed by the graphical interface63on the touch screen65. The pen tool69can be moved across the touch screen65by the user via suitable touch gestures in order to select an object of interest within the image at which the beam of measuring light should be aimed for determining the distance from this object. In the situation shown inFIG.2, the user has moved the pen tool69such that its tip points to the upper left edge corner of one of the cabinets shown in the image. The tip of the pen tool69represents a selected position71within the image. Herein, the selected position71is located at a distance from the dotted line67, and the object of interest is located away from the plane where distance measurements can be obtained by the scanning surveying system1when the alidade3is in its current rotational position about the axis9. In order to perform a distance measurement in the direction corresponding to the selected position71, the alidade has to be rotated about the axis9such that the object of interest is located in the plane where distance measurements can be obtained by the scanning surveying system1.

Therefore, when the user is satisfied with his selection of an object within the image, he can perform a further gesture instructing the controller19to perform the corresponding distance measurement. For this purpose, the controller19obtains the selected position71represented by the coordinates of the tip of the pen tool69within the image displayed on the touch screen65. For example, the position can be represented by the pixel coordinates (i, j) of the tip of the pen tool69in the displaced image.

The position data obtained from the graphical user interface63are transformed into direction data by the controller19using a suitable transformation. Data representing this transformation can be stored in the controller and may have been obtained by a suitable calibration of the cameras81and the motors6and17and corresponding angular encoders of the scanning surveying system1. Such calibration may involve recording of images using the cameras81and obtaining point clouds of objects also visible in the recorded images, and aligning the image data of the recorded image and the object data of the point cloud by suitable methods. Such methods may include methods of edge detection in both the images recorded by the cameras and the point clouds obtained by the distance measuring unit11, for example.

Based on such transformation, the controller19can determine a direction corresponding to the position of the tip of the pen tool69within the image. Based on the analysis of the position within the image, the controller19then rotates the alidade7about the axis9to a new rotational position such that the object of interest is located in the plane where distance measurements can be obtained by the scanning surveying system1. A new image recorded by the camera when the alidade3is in this new rotational position will have a field of view which is displaced relative to that shown inFIG.2. In this new recorded image, the dotted line67indicating the directions in which a distance measurements can be obtained by the scanning surveying system1will intersect the representation of the object of interest71selected by the user in the new image, as indicated by a line67′ inFIG.2.

Thereafter, it is possible to obtain a distance measurement for the object positioned around the scanning surveying system1corresponding to the position71in the image displayed on the user interface63. However, as mentioned above and as represented by the spaced apart dots of the line67′, it may not be possible to immediately obtain a distance measurement exactly from the object corresponding to the selected position, so that further steps have to be performed by the controller19until a distance measurement is obtained exactly from the selected object.

For example, assuming that the distance measuring unit11is configured such that the generated pulses of measuring light are generated at a fixed constant rate, the controller19may operate the motor17to rotate the mounting structure13about the axis14until one of the spaced apart dots of the line76coincides with the selected location71, or, in other words, until the direction of one of the emitted pulses of measuring light is selected such that the respective pulse hits the selected object. Moreover, the controller may adjust the rotation of the rotating mirror21by controlling the motor23for the same purpose.

According to other examples, the controller19may control the distance measuring unit11in order to adjust a phase of the generation period of the pulses relative to the rotation of the scanning mirror21. For this purpose, the distance measuring unit11may adjust the rotation of the scanning mirror21or the generation of the pulses of measuring light by the light source27.

In order to perform such control of the measurement direction, the correspondence between the rotational positions of the rotating mirror and the emissions of the measuring light pulses must be known. This correspondence may be determined using a detector75of the calibration unit55mounted on the alidade.FIG.4shows an image77recorded by the detector75. A plurality of dots79corresponds to a plurality of laser pulses emitted by the light source27of the optical distance measuring unit11while the rotating mirror21was in a predetermined range of rotational positions in which the pulses can be incident on the detector75. The location (x, y) of each dot79within the image77can be determined. A direction of the measuring light beam45corresponding to each dot79can be determined based on the determined location of the respective dot79in the image77and the known geometry of the detector75relative to the optical distance measuring unit11. When a direction of the beam of measuring light for given pulse can be determined based on the recorded image77, it is also possible to determine the directions of the measuring light of a pulses emitted later and incident on an object to be measured when the mirror rotates at a known speed.

Subsequent to such adjustment, the controller19may select one or more distance measurements from the multitude of distance measurements represented by the dots of line67′ inFIG.2as the distance measurements of the object corresponding to the selected location71. When plural such measurements are selected, they may originate from plural measurements obtained when the beam of measurement light was directed onto the selected object in plural revolutions of the scanning mirror. These plural results can be averaged, for example, in order to improve the accuracy of the distance measurement.

According to a still further examples, the distance measuring unit11is configured such that the controller19may trigger the emission of a pulse of measuring light. In such situation, the controller19may calculate the required time of emission of the pulse such that it is incident on the selected object, and the controller19may then determine the time for triggering the pulse based on a time spent between emission of the triggering signal and the emission of the pulse of measuring light.

FIG.3shows an exemplary image displayed on the touch screen65of the scanning surveying system according to a further specific example. Similar toFIG.2, the image has been recorded by one of the cameras81and contains objects in the surroundings of the scanning surveying system1. One of these objects is a marker object80mounted on a tripod83. The marker object80comprises a pattern81which has two black rectangles and two white rectangles in a checkerboard arrangement. This pattern is a predefined pattern, and the controller19is configured to search the recorded image for a representation of the predefined pattern. The controller19is further configured to determine a position of the representation of the predefined pattern in the image. In the illustrated example, a center of the four rectangles of the pattern81is used as a reference position of the pattern. The controller may determine the position in the recorded image where this reference position of the pattern81is located. This determined position is used as the selected position71subsequently. As illustrated above, the alidade is then rotated until the dotted line67indicating the directions in which a distance measurements can be obtained intersects the selected position71. It is then possible to measure the distance of the center of the object80from the scanning surveying system1.

The reference object80can be placed in the surroundings of the scanning surveying system1by the user in order to determine positions of these objects relative to the scanning surveying system1. For example, the illustrated reference object80can be located at a reference point on the floor used for triangulation as usual.

The pen tool69is also shown inFIG.3and can be used to select one reference object80if plural such reference objects are positioned around the scanning surveying system1and visible in the image. The controller19may then perform the distance measurement against such selected reference object80.

In the above illustrated embodiments, the light source27of the measuring unit11is mounted on the mounting structure13which is rotatable relative to the alidade7about the axis14. According to other embodiments, the light source generating the measuring light for performing measurements, such as distance measurements, is mounted on the alidade7. In such embodiments, a shaft supporting the mounting structure13on the alidade can be formed as a hollow shaft such that the measuring light generated by the light source outside of the mounting structure may enter the mounting structures by traversing the hollow shaft such that it is incident on the mirror surface25of the rotating mirror21along the axis16of rotation of the rotating mirror21.

Some embodiments have been described in connection with the accompanying drawing. However, it should be understood that the figure is not drawn to scale. Distances, angles, etc. are merely illustrative and do not necessarily bear an exact relationship to actual dimensions and layout of the devices illustrated. Components can be added, removed, and/or rearranged. Further, the disclosure herein of any particular feature, aspect, method, property, characteristic, quality, attribute, element, or the like in connection with various embodiments can be used in all other embodiments set forth herein. Additionally, it will be recognized that any methods described herein may be practiced using any device suitable for performing the recited steps.

Moreover, while illustrative embodiments have been described herein, the scope of any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and/or alterations as would be appreciated by those in the art based on the present disclosure. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to the examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive. Further, the actions of the disclosed processes and methods may be modified in any manner, including by reordering actions and/or inserting additional actions and/or deleting actions. It is intended, therefore, that the specification and examples be considered as illustrative only, with a true scope and spirit being indicated by the claims and their full scope of equivalents.