Patent Publication Number: US-9891320-B2

Title: Measurement system with a measuring device and a scanning module

Description:
The invention relates to a measurement system with a measuring device and a scanning module. 
     For acquiring objects or surfaces, use is often made of methods which progressively scan and in the process capture the topography of a structure, such as of a building, for example. In this case, such a topography constitutes a continuous sequence of points which describes the surface of the object, or else a corresponding model or a description of the surface. One conventional approach is scanning by means of a laser scanner which in each case acquires the spatial position of a surface point by the distance to the targeted surface point being measured by means of the laser and this measurement being combined with the angle information of the laser emission. From this distance and angle information, the spatial position of the acquired point can be determined and the surface can be continuously measured. In many cases, in parallel with this purely geometrical acquisition of the surface, image capture by means of a camera is also carried out, which, besides the overall visual view, also provides further information, e.g. regarding the surface texture. 
     In this regard, WO 97/40342, for example, describes a method which captures a topography by means of scanner systems installed in a stationary manner. A fixed installation point is chosen for these systems and serves as a basis for a scanning process brought about by motors. The three-dimensional location information of the respective surface point can be derived via the distance to the measured point, the angular position at the time of the measurement and the known location of the scanning apparatus. In this case, the scanner systems are specifically designed for the task of topography acquisition and scan a surface by movement of the scanner system or by variation of the beam path. 
     Moreover, scanning functions can be integrated into various other devices as additional functions. WO 2004/036145 discloses, for example, a geodetic measuring device which emits a laser beam for distance measurement from its position within the acquired range. Such measuring devices can likewise be modified for acquiring surfaces in a scanning fashion, or be operated without modification. One example thereof is motorized theodolites or total stations. 
     Other methods use mobile systems which scan a structure to be acquired by means of a movement of the scanner system, or support or supplement the scanning. Such systems are particularly suitable for acquiring linear or linearly navigable structures such as, for example, track systems, roads, tunnel systems or airfields. 
     Such acquisition processes in the prior art provide images or topographical data which substantially represent the information about the spatial distribution or arrangement relationship of surface points. If appropriate, additionally captured images allow further information to be derived. The structure and the course of the surface can thus be reconstructed comparatively well. What is disadvantageous, however, is the lack of qualitative indications about the type and constitution of the surface, in particular with regard to the internal structure or composition. In this regard, images captured in parallel with the scanning usually allow the identification of different brightness values. Furthermore, EP 1 759 172 describes a scanner system and a method for acquiring surfaces in spectrally resolved form which provides for deriving surface properties from the information obtained thereby. 
     Such laser scanners according to the prior art enable a user to acquire large surfaces and objects with a relatively short time expenditure—depending on a desired point-to-point resolution—completely and, if appropriate, with additional object information, but the accuracy of the point coordinates which can be derived in this case does not satisfy the high geodetic accuracy standards as established for example for modern measuring devices, in particular for total stations or theodolites. 
     Modern total stations generally have a compact and integrated design, wherein coaxial distance measuring elements and also computing, control and storage units are usually present in a device. Depending on the expansion stage of the total station, motorization of the targeting or sighting device and—in the case of the use of retroreflectors (for instance an all-round prism) as target objects—means for automatic target seeking and tracking can additionally be integrated. As a human-machine interface, the total station can have an electronic display control unit—generally a microprocessor computing unit with electronic data storage means—with display and input means, e.g. a keyboard. The measurement data acquired in an electrical-sensor-based manner are fed to the display control unit, such that the position of the target point can be determined, optically displayed and stored by the display control unit. Total stations known from the prior art can furthermore have a radio data interface for setting up a radio link to external peripheral components such as e.g. a handheld data acquisition device, which can be designed, in particular, as a data logger or field computer. 
     For sighting or targeting the target point to be measured, geodetic measuring devices of the generic type have a telescopic sight, such as e.g. an optical telescope, as sighting device. The telescopic sight is generally rotatable about a vertical axis and about a horizontal tilting axis relative to a base of the measuring device, such that the telescopic sight can be aligned with the point to be measured by pivoting and tilting. Modern devices can have, in addition to the optical viewing channel, a camera for sighting with angular seconds accuracy, said camera being integrated into the telescopic sight and being aligned for example coaxially or in a parallel fashion. The images or image sequences that can be acquired in this case, in particular a live image, can be represented on the display of the display control unit and/or on a display of the peripheral device—such as e.g. the data logger—used for remote control. In this case, the optical system of the sighting device can have a manual focus—for example an adjusting screw for altering the position of a focusing optical system—or an autofocus, wherein the focus position is altered e.g. by servomotors. By way of example, such a sighting device of a geodetic measuring device is described in EP 2 219 011. Automatic focusing devices for telescopic sights of geodetic devices are known e.g. from DE 197 107 22, DE 199 267 06 or DE 199 495 80. 
     Since target objects (e.g. the plumb rods with target mark, such as an all-round prism, which are usually used for geodetic purposes) cannot be targeted sufficiently precisely with the naked eye on the basis of the sighting device despite the 30-fold optical magnification often provided (i.e. not conforming to geodetic accuracy requirements), conventional measuring devices in the meantime have as standard an automatic target tracking function for prisms serving as target reflector (ATR: “Automatic Target Recognition”). For this, a further separate ATR light source—e.g. a multimode fiber output, which emits optical radiation having a wavelength in the range of 850 nm—and a specific ATR detector (e.g. CCD or CMOS area sensor) sensitive to said wavelength are conventionally additionally integrated in the telescope. By way of example, EP 2 141 450 describes a measuring device having a function for automatically targeting a retroreflective target and having an automatic target tracking functionality. 
     With such modern measuring devices, the coordinates of appropriate target points can be determined with a very high geodetic precision. What is disadvantageous in this case, however, is that a large-area object measurement e.g. with a total station means a disproportionately high time expenditure compared with a measuring process of a laser scanner on the object. 
     Therefore, a problem addressed by the invention is that of providing an additional device which, in interaction with a basic device, enables faster and improved point-by-point acquisition of a surface. 
     A further problem addressed by the invention is that of providing an improved measuring instrument which, besides an instrument-inherent highly precise target point determining possibility, enables a functionality for rapidly acquiring a multiplicity of target points with—relative to multiple precise target point determination—short time expenditure. 
     A further problem addressed by the invention is that of extending a measuring device according to the prior art in such a way that a scanning functionality is additionally provided for the measuring device. 
     These problems are solved by the realization of the characterizing features of the independent claims. Features that develop the invention in an alternative or advantageous manner can be gathered from the dependent patent claims. 
     A measurement system according to the invention comprises a measuring device comprising a base, a construction arranged on the base and pivotable about a pivoting axis, a targeting unit, in particular telescopic sight, wherein the targeting unit has at least an emission unit for emitting a first light beam, in particular a laser beam, said emission unit defining a first optical target axis, and a first distance measuring functionality for measuring a distance to an object, and a first angle measuring functionality for highly precisely acquiring at least one pivoting angle defined by a relative pivoting position of the construction with respect to the base, and a control and processing unit for data processing and for control of the measurement system. According to the invention, the measurement system has a scanning module comprising fixing means for fixing the scanning module to a receptacle corresponding to the fixing means, a beam guidance unit comprising an aperture and a second emission unit for emitting a scanning beam through the aperture onto a measurement point, said emission unit defining a second optical target axis, and being rotatable about a rotation axis in a motorized fashion, wherein the rotation axis in a received state is at a defined angle relative to the pivoting axis, in particular perpendicular, and a second angle measuring functionality for determining a rotation angle from an angular position of the beam guidance unit, wherein the measuring device has a receptacle embodied in such a way that the scanning module can be fixed in a modular manner in a defined positioning on the measuring device as a result of an interaction of the receptacle with the fixing means, and wherein the control and processing unit is embodied in such a way that the respective rotation angle, the respective pivoting angle and the respective distance for a point on the object are combined, such that a respective point position is defined by the combination, and a point cloud having a number of the point positions can be generated. 
     In one embodiment, the measuring device is a total station, theodolite or laser tracker. 
     In another embodiment of the measurement system according to the invention, a beam source for emitting the scanning beam is positioned in the beam guidance unit. 
     In yet another embodiment of the measurement system according to the invention, the scanning module comprises a beam source for emitting the scanning beam, the beam source being positioned outside the beam guidance unit, and an optical fibre for guiding the scanning beam through the optical fibre into the beam guidance unit. 
     In a further embodiment of the measurement system according to the invention, the scanning module has a second distance measuring functionality for distance measurement. 
     In one embodiment, the second distance measuring functionality is adapted to measure the distance by means of the scanning beam. 
     In another embodiment, the second distance measuring is positioned in the beam guidance unit. 
     In a further embodiment of the measurement system according to the invention, the scanning module comprises a handle. 
     The invention also pertains to a scanning module for such a measurement system. 
     A scanning module according to the invention comprises a beam guidance unit for sending out a scanning beam, said beam guidance unit being rotatable about a rotation axis in a motorized fashion, and an angle measuring functionality for determining a rotation angle from an angular position of the beam guidance unit. According to the invention, the scanning module has fixing means for fixing the scanning module to a receptacle corresponding to the fixing means, wherein the scanning module can be fixed in a modular manner in a defined positioning on the measuring device as a result of an interaction of the fixing means with the receptacle arranged on a measuring device, in particular total station, theodolite or laser tracker, and is designed for transferring the rotation angle to a control and processing unit in accordance with the measurement system as described above. 
     In one embodiment of the scanning module according to the invention, the beam source is positioned in the beam guidance unit. 
     In another embodiment of the scanning module according to the invention, the scanning module comprises an optical fibre and the scanning beam is guided through the optical fibre into the beam guidance unit. 
     In a further embodiment of the scanning module according to the invention, the scanning module has a distance measuring functionality for distance measurement. 
     In one embodiment, the distance measuring functionality is adapted to measure the distance by means of the scanning beam. 
     In another embodiment, the distance measuring functionality is positioned in the beam guidance unit. 
     In yet another embodiment of the scanning module according to the invention, the scanning module comprises a handle. 
     In a further embodiment of the scanning module according to the invention, the scanning module has an acquisition unit for acquiring the scanning beam, wherein the acquisition unit has a distance measuring functionality for measuring distance with respect to an object and/or a position-sensitive sensor for determining an impingement position of the scanning beam on a sensor. 
     In one embodiment, the acquisition unit is positioned in the beam guidance unit. 
     In another embodiment of the scanning module according to the invention, the scanning module has a data interface embodied in such a way that information, in particular angle information and/or distance information, can be transmitted from the scanning module to a device connected to the scanning module by means of the fixing means. 
     In one embodiment, the information can be transmitted between scanning module and device. 
     In yet another embodiment of the scanning module according to the invention, the scanning module has a control and processing unit for data processing and for controlling the alignment of the beam guidance unit, wherein the control and processing unit is designed in such a way that, after obtaining pivoting angle information generated by the measuring device and in particular distance information indicating the distance to an object, the respective rotation angle, the respective pivoting angle and the respective distance for a point on the object are combined, such that a respective point position on the object is defined by the combination, and a point cloud having a number of the point positions can be generated. 
     The invention also pertains to a scanning method for generating a point cloud using said measurement system. 
     A scanning method for generating a point cloud according to the invention comprises
         emitting a scanning beam,   rotationally guiding the scanning beam about a rotation axis,   pivoting the scanning beam about a pivoting axis situated at a defined angle, in particular perpendicularly, with respect to the rotation axis,   receiving the scanning beam after reflection at an object,   measuring the distance to the object and respectively determining rotation and pivoting angles,   combining the respective rotation angle, the respective pivoting angle and the respective distance for a point on the object, such that a respective point position on the object is defined by the combination, and   generating a point cloud having a number of the point positions.       

     According to the invention, at least rotationally guiding the scanning beam is effected by means of the scanning module according to the invention. 
     The invention also pertains to a computer program product for carrying out the scanning method. 
     A computer program product according to the invention comprises program code, stored on a machine-readable carrier, for controlling or carrying out the scanning method for generating a point cloud, in particular when the program is executed on an electronic data processing unit embodied as a control and processing unit of a measurement system according to the invention. 
     A measurement system according to the invention comprises a measuring device, in particular total station, theodolite or laser tracker, comprising a base, a construction arranged on the base and pivotable about a pivoting axis, and a targeting unit, in particular telescopic sight, wherein the targeting unit has at least an emission unit for emitting a first laser beam, said emission unit defining an optical target axis, and a first distance measuring functionality for measuring a distance to an object. In addition, the measuring device has a first angle measuring functionality for highly precisely acquiring at least one pivoting angle defined by a relative pivoting position of the construction with respect to the base. The measurement system additionally comprises a control and processing unit for data processing and for control of the measurement system. 
     Furthermore, the measurement system has a scanning module comprising fixing means for fixing the scanning module to a receptacle corresponding to the fixing means, comprising a beam deflection element for deflecting a scanning beam, said beam deflection element being rotatable about a rotation axis in a motorized fashion, wherein the rotation axis in a received state is at a defined angle relative to the pivoting axis, in particular orthogonally, and comprising a second angle measuring functionality for determining a rotation angle from an angular position of the beam deflection element. The measuring device furthermore has a receptacle embodied in such a way that the scanning module can be fixed in a modular manner in a defined positioning on the measuring device as a result of an interaction of the receptacle with the fixing means. Furthermore, the control and processing unit is embodied in such a way that the respective rotation angle, the respective pivoting angle and the respective distance for a point on the object are combined, such that a respective point position is defined by the combination, and a point cloud having a number of the point positions can be generated. 
     With such a measurement system, by means of the rotating movement of the deflection element, for example of a mirror, and the deflection of the scanning beam impinging thereon, it is possible to define a laser plane or a laser area, in particular of higher order. By virtue of the fact that the scanning module, in which the mirror rotates, is pivoted about a second axis by means of the measuring device, serving as a pivoting apparatus, the laser plane can now be offset continuously and an environment can thus be scanned continuously by means of the emitted laser beam. In addition, for each point on which the laser beam impinges, is reflected and is detected by a detector for the purpose of distance measurement, an emission direction of the laser beam firstly relative to the scanning module and secondly relative to the base of the measuring device is determined by means of the two goniometers. In this case, the distance measurement can be carried out e.g. according to the phase measuring principle or by means of a time-of-flight determination. By means of the combination of measured angle and respective distance variables respectively associated with a point, which combination is performed by means of the control and processing unit, it is possible to generate value arrays, wherein each array represents a coordinate of the measured point. By way of example, it is possible to combine distances and angles acquired simultaneously or within a specific time period or at defined time intervals. A point cloud which embodies the measured environment can furthermore be generated by joining together a multiplicity of such value arrays. According to the invention, the scanning module is designed in such a way that it can be detached from the pivoting unit or can be placed thereon in a modular manner by means of fixing means specifically provided for this purpose. In this case, by way of example, a stand comprising a base, which is fixedly connected to a tripod, and a construction fitted on the base and pivotable relative thereto can serve as a pivoting apparatus for the measurement system according to the invention. In addition, receptacles can be arranged on such an apparatus, which receptacles are respectively suitable for receiving the scanning module, such that a defined connection between the components arises which is releasable again in a simple manner. A receptacle suitable for this purpose and corresponding fixing means can interact and be designed in principle according to a plug-socket principle. 
     In particular, according to the invention, it is possible that the scanning module has a beam passage unit, and the targeting unit can be aligned in such a way that the first laser beam can be coupled into the scanning module by means of the beam passage unit in a coupling-in state and can be deflected in a rotating fashion as a scanning beam about the rotation axis by means of the beam deflection element, in particular wherein a scanning beam reflected at the object can be coupled out from the scanning module by means of the beam passage unit. 
     According to the invention, the scanning module of the measurement system can additionally have an acquisition unit embodied in such a way that an impingement position of the first laser beam, which can be deflected onto the acquisition unit by means of the beam deflection element in the coupling-in state, on the acquisition unit can be acquired, wherein a positioning parameter indicating a relative positioning of the scanning module with respect to the measuring device can be generated depending on the impingement position, in particular wherein the point positions can be corrected by means of the positioning parameter. 
     In the arrangement of the scanning module on the measuring device, wherein the fixing means of the scanning module are releasably connected to the receptacles of the measuring device, the first laser beam, which can be emitted by means of the targeting unit, can be aligned by a defined alignment of the targeting unit in such a way that the beam is directed onto the beam passage unit and is transmitted or coupled into the scanning module by said beam passage unit. For this purpose, the beam passage unit can be embodied e.g. with a specific optically transparent material, such that in each case that radiation of the emission unit of the measuring device having a specific wavelength is transmitted through the material. The laser radiation is then guided, for example by means of mirrors, prisms and/or lenses, to the beam deflection element, where it is deflected at a specific angle and emitted from the scanning module. By means of the rotation of the beam deflection element (and by means of the simultaneous pivoting of the measuring device) and the emission, the reflection at an object and the reception of the beam, the object can be scanned in this way. The reflected beam can thus be coupled out from the scanning module in a manner corresponding to an emission beam path and can be coupled into the measuring device and thus received again at the measuring device, and the distance to the object can thus be measured by means of the distance measuring functionality of the targeting unit. 
     According to the invention, as a result of the acquisition of the laser beam emitted by the measuring device by means of a specific acquisition unit on the part of the scanning module, e.g. by means of an area sensor (e.g. CMOS or CCD array), it is additionally possible to determine parameters with which a determination of the positioning of the scanning module on the measuring device can be performed. By way of example, from a deviation of the impinging laser beam from an image center of the acquisition unit—depending on the direction and distance from the center—it is possible to obtain information regarding the position and orientation of the scanning module relative to the measuring device. The parameters determined in this case or the measurement signals generated can be made available to the control and processing unit for determining e.g. correction parameters. The latter in turn can additionally be used for possible compensation of measurement values or can be displayed to a user graphically, e.g. on a display, such that said user can perform a position correction of the two components (measuring device and scanning module) relative to one another. 
     Furthermore, according to the invention, it is possible that the scanning module has a beam source for emitting a second laser beam as a scanning beam, and the scanning beam can be deflected in a rotating fashion about the rotation axis by means of the beam deflection element, in particular wherein the scanning module has a second distance measuring functionality for distance measurement, in particular by means of the scanning beam. 
     By virtue of the arrangement of this beam source, e.g. in the scanning module, the laser beam for scanning an object can be emitted independently of the measuring device and coupling of the beam into the scanning module need not be performed in order to provide the scanning functionality. The scanning module can additionally have a further distance measuring functionality and a distance to the object can be measurable as a result of a reception of the reflected scanning beam at the scanning module. In this configuration, therefore, both the rotation angle and the distance can be determined on the part of the scanning module. The pivoting angle can be determined by means of the measuring device. 
     In general, the pivoting angle can be communicated to a control and processing unit assigned to the scanning module and the combination, further processing and/or provision of pivoting angle, rotation angle and distance can be effected there. In particular, rotation angle and distance can be transmitted to a control and processing unit assigned to the measuring device and can be combined and provided on the part of the measuring device. Furthermore, the data for combination, processing and/or provision can be made available to a mobile or stationary unit, e.g. working computer, laptop or remote control for the system, with control and processing unit. The data transmission can furthermore take place in a cable-based manner, by means of radio, WLAN, infrared or via Bluetooth. 
     In particular, the measurement system can have at least one distance measuring sensor for measuring a distance between the scanning module and the measuring device in the received state for generating a further positioning parameter indicating the relative positioning of the scanning module with respect to the measuring device. 
     Such a sensor makes it possible to precisely determine a relative position of the scanning module on the measuring device, particularly if three such sensors—not lying on a straight line—are provided for this position determination. In this regard, distances between the components can be measured and a relative inclination of the components with respect to one another can be determined, for example, from the distances being related to one another. Accordingly, if the position and alignment of the measuring device are known, the alignment and—in the case of a defined positioning of the scanning module on the measuring device—if appropriate the position of the scanning module can be determined unambiguously by means of the sensors. From these measurements, information concerning the position and alignment can be provided to the system e.g. in a defined parameter form and can be processed further for example for purposes of compensation or adaptation of coordinates to be determined, in particular on the part of the control and processing unit. 
     In addition, according to the invention, it is possible that the measurement system has an at least two-component centering apparatus for the defined positioning of the scanning module on the measuring device, wherein a first component is assigned to the scanning module and a second component is assigned to the measuring device, in particular wherein a positioning accuracy can be measured by means of sensors for determining a relative positioning of the first component with respect to the second component. 
     In order to be able to fix the scanning module in a defined position and alignment on the measuring device or—in general—on a pivoting apparatus having a construction pivotable relative to a base, such a centering apparatus can be integrated into the measurement system or arranged thereon. As a result of an interaction of the first component of said centering apparatus with the second component, wherein respectively one of the components is assigned to the scanning module and the other is assigned to the measuring device or the pivoting apparatus, a high mounting precision can be achieved when the scanning module is mounted on the measuring device. In addition, it is possible to provide sensors with which distances between the centering components and thus a centering accuracy can be determined. Such a centering apparatus can consist, for example, of a pin as first component and a receptacle as second component, which is configured for precisely receiving the pin, in particular with a defined tolerance being complied with. At the sides of the pin receptacle which face the pin in a centering state, it is additionally possible to arrange sensors for distance measurement with respect to the pin. One known, releasable precision connection with forced centering free of play is known as an interface to the tripod on the lower part of the theodolite. The connection of the scanning module to the measuring device can be embodied in a comparable manner. 
     In addition, according to the invention, the measurement system can have a camera for acquiring an image. An image of the environment to be measured or of the object can be captured by means of said camera, wherein information acquired in the image can be used for characterizing the object or the surface thereof. By means of a combination of the image information with the measurement data generated in the scanning process, additional object properties can, in particular in a punctiform manner, be resolved, derived and processed further. Moreover, the camera can be arranged in the measurement system and embodied in such a way that the image is acquired by means of the beam deflection element, that is to say that incident light can be directed onto the camera with the aid of the beam deflection element. Furthermore, the beam deflection element can be embodied by a mirror, in particular by a polygon mirror. The deflection of the laser beam can thus be effected depending on the configuration of the mirror and its relative inclination with respect to a direction of incidence of the laser beam at a defined angle. Furthermore, the laser beam can thereby be deflected repeatedly within a complete revolution of the polygon mirror. 
     According to the invention, it is additionally possible that an inclination or tilting of the scanning module relative to the measuring device can be determined by means of a scanning of a prominent structure (by means of the scanning module and the measuring device), wherein the relative inclination is determined depending on a comparison of a scanning point cloud representing the prominent structure and generated by means of the scanning module and a measurement point cloud representing the prominent structure and generated by means of the measuring device. 
     The invention furthermore relates to a scanning module according to the invention for a measurement system according to the invention comprising a beam deflection element for deflecting a scanning beam, said beam deflection element being rotatable about a rotation axis in a motorized fashion, and an angle measuring functionality for determining a rotation angle from an angular position of the beam deflection element. Furthermore, the scanning module has fixing means for fixing the scanning module to a receptacle corresponding to the fixing means, wherein the scanning module can be fixed in a modular manner in a defined positioning on the measuring device as a result of an interaction of the fixing means with the receptacle arranged on a measuring device, in particular total station, theodolite or laser tracker. In addition, the scanning module is designed for transferring the rotation angle to a control and processing unit in accordance with the measurement system according to the invention. 
     Such a scanning module or such an attachment scanner can generate a laser plane as a result of the rotation of the laser beam about the rotation axis, wherein both the emitted laser beam and a beam reflected at an object can be guided by means of the beam deflection element or be directed in accordance with a specific measurement direction from the beam source to the object and from the object to the detector. The respective emission and reception directions of the beam can furthermore be determined by means of an incorporated angle measuring sensor. If distances to points are then measured by means of the laser beam and these distances are combined with the angles present at the time of measurement, a coordinate of the respective target point can be determined from each distance-angle combination and the point cloud can be generated by means of an accumulation or cumulation of these points. Furthermore, the scanning module with the fixing means can be positioned and fixed on an apparatus, in particular by means of a receptacle apparatus provided for this purpose. By means of this apparatus, the scanning module can be pivoted or rotated about a second axis, which is perpendicular to the rotation axis of the beam deflection element, wherein the laser plane is thus correspondingly pivoted and a generation of a point cloud of a measurement environment traversed by pivoting or of an object pivoted away can thus be carried out. The data, in particular rotation angles, generated on the part of the scanning module in this case can be made available to the control and processing unit, e.g. of a total station, for combining rotation angles with pivoting angles and distances. 
     Furthermore, according to the invention, the scanning module can have a beam passage unit for coupling in and/or coupling out the scanning beam, such that at least the coupled-in scanning beam can be deflected in a rotating manner about the rotation axis by means of the beam deflection element. As a result, a laser beam from a beam source physically separated from the scanning module can be radiated into the scanning module and guided in such a way that the beam can be used as a scanning beam and can be deflected by means of the beam deflection element. The distance measurement with respect to the object can in this case likewise be effected with the aid of the coupled-in laser beam. For this purpose, the beam reflected at the object can in turn be received on the part of the scanning module, deflected by the beam deflection element and coupled out by the beam passage unit, which is embodied for example with optically transparent material, such that the coupled-out beam is acquired by a detector for the purpose of the distance measurement. 
     In particular, according to the invention, it is possible that the scanning module has an acquisition unit for acquiring the scanning beam, wherein the acquisition unit has a distance measuring functionality for measuring distance with respect to an object and/or a position-sensitive sensor for determining an impingement position of the scanning beam on a sensor. Moreover, according to the invention, it is possible that the scanning module has a beam source for emitting the scanning beam, and the scanning beam can be deflected in a rotating manner about the rotation axis by means of the beam deflection element. With these embodiments of the scanning module, firstly, the beam can be emitted independently of external beam sources and secondly, the distance measurement can likewise be determined independently of additional distance measuring devices. In a combination of these embodiments, both the rotation angles and the distances for points on the object can be determined by means of the scanning module. In this case, the beam source can emit a laser beam in such a way that the latter impinges on the beam deflection element so as to be deflected there onto the object. Furthermore, further beam guiding means can be provided, which guide the emitted beam in such a way that the latter impinges on the beam deflection element and, if appropriate, the reflected laser beam is guided toward the detector. In this case, the laser beam source can emit, for example, a largely collimated laser beam or a divergent beam expanded in a defined manner. 
     The scanning module according to the invention can furthermore have a data interface embodied in such a way that information, in particular angle information and/or distance information, can be transmitted from the scanning module to a device, in particular measuring device, connected to the scanning module by means of the fixing means, in particular wherein the information can be transmitted between scanning module and device. By means of such a data interface, the rotation angles determined by the scanning module can be transmitted for example to the processing unit of a measuring device and can be combined there with pivoting angle and distance information for respective points. Coordinates for the respective point can in each case be generated by means of such a combination. Furthermore, the data transfer can take place in the opposite direction, from the measuring device to the scanning module, and the processing of the information can be carried out with a corresponding control and processing unit on the part of the scanning module. 
     According to the invention, it is possible that the scanning module has a control and processing unit for data processing and for controlling the alignment of the beam deflection element, wherein the control and processing unit is designed in such a way that, after obtaining pivoting angle information generated by the measuring device and in particular distance information indicating the distance to an object, the respective rotation angle, the respective pivoting angle and the respective distance for a point on the object are combined, such that a respective point position on the object is defined by the combination. In addition, it is possible that a point cloud having a number of the point positions can be generated. 
     In particular, the scanning module according to the invention can have an inclination sensor and/or a camera for acquiring an image. By means of the inclination sensor, a positioning of the scanning module can thus be determined, in particular independently of a positioning and alignment of a measuring device, and the scanning module can be brought to a defined position. By way of example, a leveling of the module can be set or checked by means of a spirit level or a compensation or correction of acquired point coordinates can be effected by means of an electronic inclinometer. With an additionally arranged camera, it is furthermore possible, for example, to acquire images of those surroundings which are acquired by the scanning module or by the pivoting of the laser plane. In this case, panoramic images representing the complete measurement environment can be generated by joining together a plurality of images. Furthermore, image information can be combined with generated data of the scanning module and additional surface information, e.g. color, contours or reflection behavior, of measured objects can thus be generated. 
     The invention additionally relates to a measuring device, in particular total station, theodolite or laser tracker, for a measurement system according to the invention, comprising a base, a construction arranged on the base and pivotable about a pivoting axis, and a targeting unit, in particular telescopic sight, wherein the targeting unit has at least an emission unit for emitting a laser beam, said emission unit defining an optical target axis, and a distance measuring functionality for measuring a first distance to an object. In addition, provision is made of an angle measuring functionality for highly precisely acquiring at least one pivoting angle defined by a relative pivoting position of the construction with respect to the base. 
     The measuring device furthermore has a receptacle embodied in such a way that a scanning module can be fixed in a modular manner in a defined positioning on the measuring device as a result of an interaction of the receptacle with fixing means of the scanning module. Furthermore, provision is made of a data interface embodied in such a way that information, in particular angle information and/or distance information, can be obtained, in particular from the scanning module, and a control and processing unit for data processing and for controlling the measuring device, wherein the control and processing unit is embodied in such a way that, after obtaining rotation angle information generated by the scanning module and in particular distance information indicating a second distance to the object, the respective rotation angle, the respective pivoting angle and the respective first or second distance for a point on the object are combined, such that a respective point position on the object is defined by the combination. It is possible that a point cloud having a number of the point positions can additionally be generated. 
     With a measuring device according to the invention, by means of a combination with a scanning module according to the invention, it is possible to produce a system which inherently unites both the advantages e.g. of a laser scanner, in particular with regard to the measurement speed advantages, and the advantages e.g. of a total station, in particular with regard to the measurement accuracy. By means of the measuring device, for example, a target point can be measured highly precisely and its coordinates can be determined exactly. However, if e.g. a rapid overview scan of an environment is required for orientation, coarse targeting or creation of a terrain model, on account of a significantly higher measurement speed, a scanning module fitted on the measuring device can be pivoted by means of drives for the alignment of the targeting unit and a rapid scan of an environment can thus be carried out. The measuring device can thus form a system component of the measurement system with which a scanning module can be combined and which is designed for pivoting the scanning module. For this purpose, receptacles corresponding to fixing means of the scanning module can be provided for fixing. 
     A further aspect of the invention relates to a scanning method for generating a point cloud comprising
         emitting a scanning beam,   rotationally deflecting the scanning beam about a rotation axis,   pivoting the scanning beam about a pivoting axis situated at a defined angle, in particular perpendicularly, with respect to the rotation axis,   receiving the scanning beam after reflection at an object,   measuring the distance to the object and respectively determining rotation and pivoting angles,   combining the respective rotation angle, the respective pivoting angle and the respective distance for a point on the object, such that a respective point position on the object is defined by the combination, and   generating a point cloud having a number of the point positions.       

     In this case, at least rotationally deflecting the scanning beam is effected by means of a scanning module according to the invention. In particular, according to the invention, at least pivoting the scanning beam can be effected by means of a measuring device according to the invention. 
     In particular, a synchronization signal can be exchanged in order to control or coordinate a respective combination of the measurement values (e.g. rotation angles, pivoting angle, distance for a point on the object) of the sensors. 
     The invention furthermore provides a computer program product comprising program code, stored on a machine-readable carrier, for controlling or carrying out the scanning method according to the invention for generating a point cloud, in particular if the program is executed on an electronic data processing unit embodied as a control and processing unit of a measurement system according to the invention. 
    
    
     
       The method according to the invention, the measurement system according to the invention, the scanning module and measuring device according to the invention are described in greater detail purely by way of example below on the basis of specific exemplary embodiments illustrated schematically in the drawings, further advantages of the invention also being discussed. In detail: 
         FIGS. 1 a - d    in each case show an embodiment of a scanning module according to the invention; 
         FIGS. 2 a - d    in each case show a measurement system according to the invention with a measuring device and a scanning module fixed thereto; 
         FIG. 3  shows a further embodiment of a measurement system according to the invention with measuring device and scanning module with distance sensors and a laser beam directed onto a detector; 
         FIGS. 4 a - c    show a further embodiment of a measurement system according to the invention with a centering apparatus; 
         FIG. 5  shows a measuring process with a measurement system according to the invention for calibration; 
         FIGS. 6 a - b    in each case show a further embodiment of a measurement system according to the invention with a pivoting apparatus and a scanning module; 
         FIG. 7  shows a further embodiment of a measurement system according to the invention with pivoting apparatus, scanning module and an attached GNSS module; 
         FIGS. 8 a - c    in each case show a further embodiment of a scanning module according to the invention; and 
         FIGS. 9 a - b    in each case show a measurement system according to the invention with a measuring device and a scanning module fixed thereto. 
     
    
    
       FIGS. 1 a  to 1 d    in each case show an embodiment of a scanning module  10  according to the invention or of an attachment scanner which can be mounted by means of a fixing apparatus  18  on a pivoting apparatus, e.g. a theodolite or a total station, and can thus extend this apparatus by a scanning functionality. 
     In a first embodiment ( FIG. 1 a   ), the attachment scanner  10  has a mirror  11  as a deflection element, which mirror can be rotated about a horizontal axis  12 , wherein the rotation can be brought about by a motor  14  and a rotation angle can be acquired by means of an angle measuring sensor  13 . In addition, the module  10  is equipped with a light emitting module, e.g. a laser module  15 , in particular with a beam source such as, for example, a laser diode for emitting a laser beam and with an and receiving unit for detecting reflected laser radiation. The emitted laser beam can be aligned via an optical beam guiding element  17  onto the mirror  11  and from there onto a measurement point. Furthermore, the attachment scanner  10  is equipped with a camera  16 , the image field of which is likewise directed via the optical beam guiding element  17  onto the mirror  11  and from there in the direction of the measurement point. 
     In a second embodiment of the scanning module  10  according to the invention ( FIG. 1 b   ), the attachment scanner  10  has an optical beam guiding element  17   a , by which a laser beam aligned (here: from below) onto the module  10  can be defected onto the mirror  11  and from there onto the measurement point. With this embodiment, a laser beam from an external source not provided in the scanning module  10  can be deflected by means of the components of the module  10  and can be used for scanning. Furthermore, by means of the mirror  11  received, reflected radiation can be guided onto a detector that is likewise provided externally. Consequently, the scanning module  10  can be embodied without its own laser module  15 . It is once again possible for the rotation of the mirror  11  to be carried out by a motor  14  and the measurement of the respective rotation angles to be carried out by means of a goniometer  13 . In addition, in this embodiment a locking apparatus  19  is provided, with which the scanning module  10  can be connected e.g. to a measuring device in suitable positioning or by means of which the coupling-in of the laser beam can be carried out exactly. 
     In the third embodiment ( FIG. 1 c   ), the attachment scanner  10  is equipped with an optical beam guiding element  17   b , by means of which a laser beam aligned from below onto the module  10  can be deflected onto the mirror  11  and from there onto the measurement point. Here, the rotatable mirror  11  is arranged eccentrically with respect to a vertical pivoting axis  22  of a pivoting apparatus. In addition, the scanning module  10  once again has a motor  14  for driving the rotation and a goniometer  13  for determining the rotation angle of the mirror  11 . Moreover, a beam passage unit  9  is shown, by means of which a laser beam can be coupled into and out of the scanning module  10 . For this purpose, the beam passage unit  9  can be embodied with an optically transparent window, for example, through which the beam can be transmitted on account of the specific transmission properties. 
       FIG. 1 d    shows a fourth embodiment of the scanning module  10 , wherein a laser beam aligned from below onto the module  10  impinges directly on a polygon mirror  11   a , which can be rotated about the rotation axis  12  by means of motor  14  and which deflects the beam. In this case, the beam is once again coupled into the scanning module by a beam passage unit  9 . The laser beam can be generated by an external beam source and reflected radiation can be directed by means of the polygon mirror  11   a  onto a likewise external detector, which can be provided for example in a measuring device, as a result of which the scanning module  10  can be embodied without a laser module  15 . In this embodiment, too, provision is made of an angle measuring functionality  13  for determining the rotation angles. 
       FIG. 2 a    shows a first embodiment of a measurement system  50  according to the invention, wherein a scanning module  10  is combined with a measuring instrument  20 , e.g. a theodolite or total station. In this case, the scanning module  10  corresponds to a module  10  according to the invention as shown in  FIG. 1 a    with mirror  11 , goniometer  13 , motor  14 , rotation axis  12 , laser module  15  and camera  16 . In a scanning process, in this case the mirror  11  of the attachment scanner  10  can rotate about the horizontal axis  12  at high speed. 
     In this case, the entire upper part of the measuring device  20 , the construction  20   a  designed for receiving the scanning module  10 , can simultaneously be pivoted or rotated at lower speed about the vertical pivoting axis  22  relative to the base  20   b  of the measuring device  20 . This can be brought about by a motor  26  arranged in the measuring instrument  20 . During scanning, the laser module  15  can emit a laser beam  60  which is guided via an optical beam guiding element  17  onto the mirror  11  and from there e.g. onto the measurement point. By means of the laser beam  60 , its reflection at a surface and the acquisition by the detector, it is thus possible to carry out a distance measurement to the measurement point on the surface. The coordinates of the measurement point can be calculated from the measured distance and also from the vertical angle or rotation angle acquired by the angle sensor  13  and a horizontal angle or pivoting angle determined by an angle sensor  24  arranged in the pivoting apparatus  20 . In addition, the measuring instrument  20  has a targeting unit  30 , in particular a telescope, said targeting unit being pivotable or rotatable about a second vertical axis  21 . In this case, the targeting unit  30  can be pivoted by means of a further motor  25 , wherein a further pivoting angle can be measured by an angle measuring sensor  23 . 
       FIG. 2 b    shows a second embodiment of the measurement system  50  according to the invention with attachment scanner  10  and measuring device  20 . In this case, the telescope  30  of the measuring instrument  20  can be aligned upward, substantially parallel to the vertical axis  22  thereof, and can be held or secured in this position by means of the locking apparatus  19 . For scanning purposes, a laser beam  60  can be directed from the laser emitter  27  in the telescope  30  via an optical deflection element  29  in the telescope  30  onto an optical beam guiding element  17   a  in the attachment scanner  10  and from there onto the mirror  11  thereof and, if appropriate, furthermore subsequently onto the measurement point. In this case, the mirror  11  of the attachment scanner  10  rotates at high speed about the rotation axis  12 . The construction  20   a  of the measuring device  20  can simultaneously pivot or rotate at lower speed about the vertical axis  22 . In this case, too, the coordinates of the measurement point can be calculated from the measured distance and also from the rotation angle acquired by the angle sensor  13  and the pivoting angle determined by the angle sensor  24 . For this purpose, the rotation angles, pivoting angles and distances for a respective measurement point are combined e.g. by means of a processing unit provided on the measurement system  50 . During the scanning process, the image field of the camera  28  of the measuring instrument  20  can be aligned via the elements  17  or  29  and  17   a  and the mirror  11  onto the measurement point and image data can be acquired. 
       FIGS. 2 c  and 2 d    show a third and a fourth embodiment of the measurement system  50  according to the invention with respectively a measuring device  20  and a scanning module  10  corresponding to the embodiments in accordance with  FIGS. 1 c  and 1 d   . Both embodiments of the measurement system  50  use a laser beam  60  which is emitted by a beam source  27 , in particular laser diode, of the targeting unit  30  and is guided into the scanning module  10 . A beam passage unit  9  is in each case provided for this purpose. Depending on the embodiment, the beam passage unit  9  can be designed for example as mirror protection or as means for enlarging the field of view of the camera  28 . The beam  60  can be directed by means of a beam deflection element  17   b  onto the mirror  11  or onto the polygon mirror  11   a  and can be directed onto a surface to be measured. In  FIG. 2 c   , the laser beam  60  is in this case emitted from the mirror  11  eccentrically with respect to the pivoting axis  22 , wherein a laser plane lying parallel to the axis  22  can be generated. 
     The respective angles and the distance which are acquired at the same time or at defined time intervals that can be assigned to one another can be combined for a point measurement. In the embodiment in accordance with  FIG. 2 a   , for example, this acquisition can be controlled by the measuring device by virtue of the fact that, at the time of measurement of the horizontal angle by the angle sensor  26 , via a data interface, a trigger signal is sent to the attachment scanner  10 , which triggers there the measurement of the vertical angle by the angle sensor  13  and of the distance. Moreover, at the time of measurement of the vertical angle and of the distance, the attachment scanner  10  can send a trigger signal to the measuring instrument and initiate there a simultaneous triggering or a triggering within a specific time period of the horizontal angle measurement. Furthermore, the trigger signal can be sent continuously e.g. upon each point measurement or at specific angle positions e.g. once per revolution of the mirror  11 , in particular in the nadir position thereof. In particular, the measurement data can be interpolated between the trigger signals. 
     The measurement data (vertical angle and/or distance) determined by the scanning module  10  can be communicated via a data interface to the measuring device  20 , where they can be stored together with a horizontal angle determined by the measuring device  20 . In particular, in a control and processing unit of the measuring device  20 , point coordinates can be calculated from the angles and the distance and said point coordinates can be stored. 
     In addition, it is also conceivable to communicate the horizontal angle from the measuring device  20  to the attachment scanner  10 , where said horizontal angle can be stored together with the vertical angle and the distance on a storage module or point coordinates can be calculated therefrom by means of a corresponding control and processing unit of the attachment scanner  10 . If the horizontal angle is acquired and transmitted e.g. at a lower measurement rate, the measured angles can be interpolated in the processing unit, such that only a comparatively small number of angle values need be transmitted from the measuring device  20  to the attachment scanner  10 , e.g. only one value per vertical revolution of the mirror  11  or polygon mirror  11   a . Furthermore, a compression, e.g. by filtering, of the measurement data or point coordinates can be effected before the data transmission or storage. A very efficient data compression is possible with an angle triggering, wherein the angle sensor of the fast axis represents the trigger source. In this case, it suffices to store only the sequence of the distance measurement values with the fewer measurement angles of the slow axis  22 . The point positions and the point cloud associated therewith can be generated from such a greatly reduced sequence of measurement values. 
     Furthermore, it is possible to communicate the horizontal angle from the measuring device  20  and also the vertical angle and the distance from the attachment scanner  10  to an external processing unit, e.g. to a mobile remote control situated neither in the measuring device  20  nor in the attachment scanner  10 . 
     The communication between measuring instrument  20 , attachment scanner  10  and e.g. a controller can be effected via a wire connection, via radio (e.g. Bluetooth or WLAN) and/or via an optical, inductive or capacitive interface. For this purpose, suitable transmitting and receiving units can be provided at the individual components of the measurement system  50  according to the invention. The energy supply of the attachment scanner  10  can furthermore be effected by an integrated battery or by from the measuring device  20  by means of electrical contact-making. 
     In order to ensure a high accuracy for a coordinate measurement by means of the scanning module  10 , an external orientation of the scanning module  10  can be determined. For this purpose, it is possible to mount the scanning module  10  at a defined position (whereby three translation parameters are known) and in a defined alignment (whereby three rotation parameters are known) on the measuring device  20 . The measuring device  20  can furthermore be calibrated into a measurement environment, in particular by the targeting of target points with known coordinates, as a result of which the position and alignment of the measuring device  20  are known. In addition, a deviation from the defined position and/or alignment can be acquired by sensors and taken into account in e.g. the calculation of the coordinates of the measurement points. In this case, mounting in a defined position and/or alignment can be realized for example by means of a mechanical fixing or centering device, whereby a high positional accuracy can be made possible. 
     In addition to the scanning process by means of the scanning module  10 , at the same time a “scanning” can also be effected by means of the measuring device  20 . In this case, the telescope  30  can rotate at comparatively low speed about the horizontal axis  21 . In this case, the horizontal angle can be measured by the angle sensor  24  and the vertical angle by the angle sensor  23 —the distance can be determined by means of the laser module  27 . From these measurement data it is possible to calculate the coordinates of measurement points, which can form a point cloud in total. 
     After the scanning, therefore, two point clouds can be present. A first point cloud having high resolution but low accuracy, which was acquired by the scanning module  10 , and a second point cloud having lower resolution but high accuracy, which was generated by the measuring device  20 . By means of a matching of the two point clouds, it is thus possible to detect or correct systematic faults e.g. of the scanning module  10 . 
     If the attachment scanner  10  does not have its own camera, the image capture can be carried out by a camera  28  provided on the measuring device  20 . For this purpose, during a scanning process carried out by means of the attachment scanner  10 , the telescope  30  of the measuring device  20  can pivot or rotate at lower speed about the horizontal axis  21  thereof. With the camera incorporated in the telescope  30  (on-axis camera, i.e. the camera  28  acquires an image corresponding to the alignment of the laser beam  60 , in particular coaxially), images can be captured and, at the same time, the horizontal angle and the vertical angle of the telescope  30  can be acquired. By means of these angles, given a known position and alignment of the attachment scanner  10 , the image data can be combined with the scanning data. Furthermore the measurement system  50  can be equipped with an overview camera, wherein the overview camera has a larger field of view in comparison with the camera  28  and can thus acquire a larger region of a measurement environment. The outputting of the images thus acquired can offer a user, in particular, an additional benefit with regard to the orientation and targeting of targets in the terrain. 
       FIG. 3  shows a measuring device  20  with scanning module  10  in accordance with the embodiment in  FIG. 2 a   , wherein the attachment scanner  10  is equipped with an additional optical element  31 , e.g. lens or filter, in order to ensure an optical imaging suitable for determining a position of a laser point on the camera  16 . Distance measuring sensors  32  for determining position and alignment parameters are additionally provided. If the distance between the attachment scanner  10  and the measuring device  20  is acquired at at least three different positions (which do not lie on a straight line) by means of such sensors  32 , a vertical distance and also the longitudinal and transverse inclinations of the scanning module  10  can be derived from these measurements. 
     Additional parameters can be determined by virtue of the fact that the laser beam  60  is directed from the measuring device  20  via the mirror  11  and the beam guiding element  17  onto the camera  16 , which can have a position-sensitive sensor, of the scanning module  10 . For this purpose, the telescope  30  of the measuring device is aligned upward parallel to the vertical axis and the mirror  11  of the attachment scanner  10  is aligned downward. The parameters can be derived from an acquired position of the laser point in a captured image of the position-sensitive sensor. Conversely, the laser beam  60  can also be imaged from the laser module  15  of the attachment scanner  10  onto the camera sensor  28  of the measuring device  20  and offset parameters and angle parameters can be derived from this position of the laser point. For this purpose, the camera sensor  28  can likewise be embodied and evaluated position-sensitively. 
     In particular—e.g. in the case of a coarse alignment of the telescope  30  parallel to the vertical axis  22 —in the case of an approximate alignment the angle deviation can be acquired by means of the angle sensor  23  and taken into account for example in a coordinate calculation. In addition, calibration parameters of the measuring instrument  20  (e.g. corrections of the target line error and/or tilting axis error) and of the attachment scanner  10  can concomitantly influence the calculation. 
     In addition, the attachment scanner  10  can be equipped with an inclination sensor that acquires the inclination in longitudinal and transverse directions in relation to the gravitational field. Said sensor can be used to correct the measurements of the attachment scanner with regard to the deviation of the pivoting axis (vertical axis) from a perpendicular direction. 
     Furthermore, a relative inclination of the attachment scanner  10  in relation to the measuring device  20  can be calculated from the difference between the measured inclinations of the attachment scanner  10  and an inclination determined by an inclination sensor of the measuring device  20 . 
     A horizontal pivoting of the attachment scanner  10  in relation to the measuring device  20  can additionally be effected by the scanning of a prominent structure, for example a vertical house edge, by the attachment scanner  10 , on the one hand, and by the measuring device  20 , on the other hand, wherein the difference angle can be determined on the basis of a horizontal offset of the two point clouds that can be obtained in this case. 
     The attachment scanner  10  can furthermore be equipped with a storage module, such that the acquired measurement data can be stored directly in the attachment scanner. In parallel therewith, the measurement data of the measuring device  20  can be stored on a memory arranged there. The synchronization of the attachment scanner  10  and of the measuring device  20  can be effected by means of a trigger signal communicated from the measuring device  20  to the attachment scanner  20  (or vice versa). In this case, the synchronization can be effected on the basis of a time signal respectively received by the measuring device  20  and the attachment scanner  10 , wherein a time receiver is respectively assigned to the two components. In particular, the synchronization can also be effected by two GPS receivers which each receive the GPS time, a respective GPS receiver being arranged on the measuring device  20  and attachment scanner  20 . The acquired time signals can in each case be combined with measurement values (by way of example, a time stamp can be assigned to the measurement data) and a subsequent assignment of the measurement values can be effected by means of the combination. 
       FIG. 4 a    shows a scanning module  10  with a measuring instrument  20 , wherein a mechanical locking or centering of the two components is additionally shown, in particular in joint consideration with  FIGS. 4 b  and 4 c   . In this case, the beam exit end  33 , in particular the objective lens, of the telescope  30  is received in its illustrated alignment by the locking apparatus  19  in such a way that a lateral displacement which is caused thereby and which is made possible by the suitable embodiment of the fixing apparatuses  18  brings about a centering of the attachment scanner  10  relative to the measuring instrument  20 . In particular,  FIG. 4 c    illustrates a locking apparatus  19  in which the attachment scanner  10  is locked with a coarse positioning relative to the beam exit end  33  and a remaining offset with respect to a desired position can be acquired by means of distance sensors  34  and taken into account computationally in the coordination determination for the measurement point. 
       FIG. 5  shows a measuring process with a measurement system  50  according to the invention, in particular for calibrating the system  50 . During the calibration, it is possible to determine parameters which describe e.g. mechanical deviations from a desired geometry and are used for calculating compensations or corrections of the measurement values. Internal calibration parameters such as e.g. the angle of the mirror  11  in relation to the rotation axis  12  thereof or the impingement angle of the laser beam  60  on the mirror  11  can generally be determined after the manufacture of the scanning module  10 . These parameters can be checked after relatively long time periods of use of the device by means of corresponding methods and can be corrected, if appropriate, in order to be able to ensure a high precision of the system  50 . Furthermore, the measurements described below can also serve to determine an external orientation of the attachment module  10  in relation to the measuring device  20 , in particular in combination with measurement by additional sensors. 
     For calibration purposes, measurements are carried out which can be used to determine the calibration parameters—usually by means of a compensation calculation. For this purpose, e.g. the measuring device  20  can be aligned with a target point  41  on an object  70  at a known distance. From the known distance and also from the angles acquired by the angle sensors  23  and  24 , it is possible to determine a reference target direction  42  in the coordinate system of the measuring device  20 . At the same time, the mirror  11  can be aligned with the point  41  marked by a laser beam  40  in such a way that said point is imaged as a laser point in the image of the camera  16  of the scanning module  10 . A direction  43  can be determined by measurements by means of the angle sensors  13  and  24  and the determination of the position of the laser point  41  in the captured camera image. The calibration parameters can be determined by a matching of the reference directions  42  and the directions  43  with a plurality of points, wherein the number and the spatial distribution of the point positions to be determined are dependent on the parameters to be determined. 
     Measurements onto the same point  41  in two circle positions are particularly advantageous, that is to say that after the point has been measured in the first circle position, the measuring device  20  with the attachment scanner  10  is rotated horizontally by 180° and then the telescope  30  of the measuring device  20  and the mirror  11  of the attachment scanner  10  are rotated vertically in such a way that the same point  41  can be measured in the second circle position. 
     The method can also be carried out oppositely, by virtue of the laser beam  60  of the attachment scanner  10  marking a point  41  and the latter being acquired by the camera  28  in the measuring device  20 . 
     If the distance to the point is not known, a distance measurement can be carried out by means of the laser module  27 . From the distance and the angles determined by the angle sensors  23  and  24 , it is possible to determine the coordinates of said point  41  in the coordinate system of the measuring device  20 . From these coordinates, it is possible to derive a reference target direction  43  for the attachment scanner  10 . 
     If neither measuring device  20  nor attachment scanner has a camera, the measurements required for the calibration can be carried out manually in a modified form. For this purpose, the laser beam  60  of the attachment scanner  10  can be aligned with a significant point  41 , e.g. a target mark. In this case, the angles are measured by the angle sensors  13  and  24  and the direction  43  is thus determined. By means of the rotation of the measuring device  20  about the vertical axis  22  and by means of the rotation of the telescope  30  about the horizontal axis  21 , the laser beam  40  of the measuring device  20  is aligned with exactly the same point and the angles are measured by the angle sensors  23  and  24  and the reference direction  42  is derived therefrom. The telescope  30  can be aligned by the laser beam  40  being made to coincide with the significant point  41 , e.g. the target mark, or by conventional targeting by means of a reticle. Calibration parameters which relate to the distance measurement of the attachment scanner  10 , e.g. distance offset and/or distance scaling, can be determined on the basis of measurements of the distance to identical points at different distances by means of the measuring device  20  and the attachment scanner  10 . 
     In particular, the scanning module  10  can furthermore be pivoted or rotated by means of a motorized pivoting apparatus  80 . In this respect,  FIGS. 6 a  and 6 b    in each case show a further embodiment of a measurement system  50  according to the invention with a pivoting apparatus  80  and a scanning module  10 .  FIG. 6 a    illustrates an attachment scanner  10  with a first embodiment of a pivoting apparatus  80 . The apparatus  80  has a lower base  80   b  and an upper construction  80   a , which is pivotable about the vertical axis  81 , wherein the pivoting can be effected by a motor  83  and the pivoting angle can be acquired by an angle sensor  82 . 
     A second embodiment of the motorized pivoting apparatus is shown in  FIG. 6 b   . The latter is additionally equipped with a laser module  84 , a camera  85  and an optical deflection element  86 . A scanning process with these two embodiments can be carried out analogously to the embodiments in accordance with  FIGS. 2 a  and 2 b   . Both embodiments can additionally be equipped with an, in particular two-dimensional, inclination sensor  87 , a magnetic compass, a display, in particular a touch-sensitive display, and/or a detachable operating element. 
       FIG. 7  shows a further embodiment of a measurement system  50  according to the invention with pivoting apparatus  80 , scanning module  10  and an attached GNSS unit or GNSS antenna  90 . For this purpose, the attachment scanner  10  can be equipped with fixing apparatuses  18   a  for mounting the GNSS antenna  90 . In addition, the pivoting apparatus  80  has a display  88  for displaying information and an operating panel  89 , in particular for inputting control commands. 
       FIGS. 8 a  to 8 c    show three further embodiments of an attachment scanner  100  which can be mounted by means of a fixing apparatus  18  as a scanner module on a pivoting apparatus, e.g. a theodolite or a total station, and can thus extend this apparatus by a scanning functionality. In these embodiments, the attachment scanner  100  has a beam guidance unit  300  being pivotable or rotatable about a first vertical axis  120  and having an aperture for emitting a light beam, e.g. a laser beam, and receiving reflections of the beam. In this case, the targeting unit  30  can be pivoted by means of a motor  140 , wherein a pivoting angle can be measured by an angle measuring sensor  130 . 
     In a fifth embodiment shown in  FIG. 8 a   , the beam guidance unit  300  of the attachment scanner  100  is equipped with a laser module, in particular with a beam source such as, for example, a laser diode for emitting a laser beam and with an and receiving unit for detecting reflected laser radiation. The emitted laser beam is guided from the beam guidance unit  300  onto a measurement point. Furthermore, the beam guidance unit  300  is equipped with a camera. 
     In a sixth embodiment shown in  FIG. 8 b   , the laser module  150  is provided outside the targeting unit  30 , and the emitted laser beam is guided into the beam guidance unit  300  by means of an optical fibre  170 . 
     In a seventh embodiment shown in  FIG. 8 c   , the beam guidance unit  300  is constructed to comprise a handle  190  in order to allow easier transport and handling of the beam guidance unit  300 . 
       FIGS. 9 a  and 9 b    show two exemplary embodiments of a measurement system  50  according to the invention, wherein a scanning module  100  according to  FIGS. 8 a  and 8 b    is combined with a measuring instrument  20 , e.g. a theodolite or total station. 
     In  FIG. 9 a   , the scanning module  100  corresponds to a module  100  according to the invention as shown in  FIG. 8 a    with beam guidance unit  300 , rotation axis  120 , measuring sensor  130  and motor  140 . In a scanning process, in this case the beam guidance unit  300  of the attachment scanner  100  can rotate about the horizontal axis  120 . In this case, the entire upper part of the measuring device  20 , the construction  20   a  designed for receiving the scanning module  10 , can simultaneously be pivoted or rotated at lower speed about the vertical pivoting axis  22  relative to the base  20   b  of the measuring device  20 . This can be brought about by a motor  26  arranged in the measuring instrument  20 . During scanning, the laser module can emit a laser beam which is guided onto the measurement point. By means of the laser beam, its reflection at a surface and the acquisition by the detector, it is thus possible to carry out a distance measurement to the measurement point on the surface. The coordinates of the measurement point can be calculated from the measured distance and also from the vertical angle or rotation angle acquired by the angle sensor  130  and a horizontal angle or pivoting angle determined by an angle sensor  24  arranged in the pivoting apparatus  20 . In addition, the measuring instrument  20  has a targeting unit  30 , in particular a telescope, said targeting unit being pivotable or rotatable about a second vertical axis  21 . In this case, the targeting unit  30  can be pivoted by means of a further motor  25 , wherein a further pivoting angle can be measured by an angle measuring sensor  23 . 
     In  FIG. 9 b   , the scanning module  100  corresponds to a module  100  according to the invention as shown in  FIG. 8 b    with beam guidance unit  300 , rotation axis  120 , measuring sensor  130 , motor  140 , laser module  150  and optical fibre  170 . 
     It goes without saying that these illustrated figures merely illustrate possible exemplary embodiments schematically. The different approaches can likewise be combined according to the invention with one another and also with systems and methods for measuring surfaces or objects and with measuring devices from the prior art.