Abstract:
Method for determining, with geodesic precision, the position of a target point on a target object by using a geodesic measuring device, said method comprising a sighting device which comprises at least one objective unit that defines an optical line of sight, an electronic distance measuring unit, and a thermal imaging camera for recording a thermal image in the direction of the optical line of sight. An angle measuring function is provided for recording the line of sight alignment, and a control unit is provided for controlling the angle measuring function, the thermal imaging camera. In a thermal imaging mode when a measurement procedure is triggered, position data of the sighted target point which are determined in said measurement procedure are linked to temperature information which is read out from the thermal image for the target point at which the line of sight is aimed.

Description:
FIELD OF THE INVENTION 
     The invention relates to a geodesic measuring device for measuring distances and angles with respect to points on an object and a method for measuring distances and angles with respect to points on an object. 
     BACKGROUND 
     Generally known examples of geodesic measuring devices are the theodolite or the total station. Geodesic measuring devices are used for determining distances and for simultaneously acquiring corresponding angles with respect to target points. Such systems are in widespread use primarily in the field of landscape surveying or for positioning tasks in industry. Both areas of use demand the exact determination of the variables of distance and angle over in some instances large distances, in order e.g. to be able to precisely plan and implement subsequent building development of a surveyed terrain or in order to control a machine incorporated into a production process. 
     One known extension of these measuring devices is combination with an image recording unit, usually integrated into the device. Thus, in addition to the variables determined, e.g. a camera can be used to acquire images of an environment in which the target points are situated. This combination opens up the possibility, inter alia, of carrying out a measurement e.g. by means of image-assisted target point seeking. Moreover, the recording of an optical image makes it possible to bring about a target identification or target tracking and thus a further facilitation and automation of the measuring process. An automatic target tracking is known from EP 2 141 450, for example, wherein a sighting direction of a measuring station is automatically aligned with a target on the basis of a processed image. 
     Furthermore, an image of a recorded environment to be measured can be displayed on a display fitted to the measuring device. By means of an input unit, a user is thus enabled to select specific points of interest on the image and to determine the exact positions of the points with the aid of the distance and angle measuring devices incorporated in the measuring device. 
     EP 1 314 959 and WO 2004/036145 disclose for example geodesic measuring devices comprising an electronic display and control device which enable screen-based operation. 
     In a two-dimensional representation of an optical image, it is accordingly possible to define points with respect to which a measurement, i.e. the determination of distance and/or angle, is effected. On the basis of an image that can be acquired by various recording means, targets can be identified and tracked by means of image processing methods, such that an automatic measurement is possible in principle on this basis thus provided. In addition, with such an embodiment—by means of the arrangement of at least one camera with an extended acquisition spectrum—ranges and object properties which are outside the visual accessibility of the human eye can be made accessible to the measurement. 
     By means of these geodesic measuring devices, points selected beforehand, e.g. on a display, can be sighted, moved to and subsequently measured. For the user of such a device, this significantly simplifies the operability and affords the major advantage with regard to ergonomics that the device need not necessarily be aligned through an eyepiece, but rather can be controlled on the basis of the display or via a remote control. 
     What is disadvantageous, however, is that only angle and distance data can be ascertained with respect to an appropriate point and, furthermore, no further information about e.g. the object on which the point is situated can be acquired. Furthermore, no assignment or linking of position information to further image-based object- or target-point-related data takes place. 
     Additional information about an object or the surface thereof can be acquired e.g. on the basis of a camera-recorded color value or else by means of a thermal imaging camera. By means of this information, it is possible to derive specific object properties or properties of at least parts of objects. By way of example, thermal imaging cameras can be used for identifying irregularities in a heat distribution or heat leaks and it is thereby possible to ascertain such locations e.g. at buildings. A thermal detector can also be used in fire fighting—for finding a fire source—or for target identification when darkness prevails. 
     One problem in the course of using a thermal imaging camera that can be handheld arises when an exact position of a conspicuous feature identified by the camera or e.g. the dimensioning of said conspicuous feature is intended to be determined. Such a positioning or determination of the extent cannot be performed solely from a manually acquired thermal image, which can then usually be displayed on a display at the camera. However, exact position determination for such conspicuous features would be desirable inter alia in the case of e.g. construction measures to be performed for the purpose of improving insulation or repair work. 
     SUMMARY 
     Accordingly, a problem addressed by the present invention is that of providing a device and a method whereby thermal energy properties, in particular temperature properties, of objects can be locally correlated with position information of points on said objects. 
     One specific problem addressed by the invention is that of providing a device and a method whereby information can be derived from thermal energy properties and said information can be locally correlated with position information of points. 
     A further specific problem addressed by the invention is that of providing a system whereby objects can be identified rapidly and reliably on the basis of their thermal energy properties, in particular temperature properties. Furthermore, position information is intended to be able to be assigned to the identified objects. 
     These problems are solved by the realization of the characterizing features of the independent claims. Features which develop the invention in an alternative or advantageous manner can be gathered from the dependent patent claims. 
     A method according to the invention for determining, with geodesic precision, the position of a target point on a target object is carried out using a geodesic measuring device comprising a sighting device, in particular a telescopic sight, wherein the sighting device is pivotable relative to a base of the measuring device in order to change the alignment thereof and at least has an objective unit that defines an optical aiming axis, an electronic distance measuring unit, and a thermal imaging camera for acquiring a thermal image, in the direction of the optical aiming axis. Geodesically precise position determination (geodesic precision) for a target should be understood to mean, depending on the respective measurement requirement, determining the position of the target present at a distance of up to hundreds of meters (or a few kilometers) with a precision (resolution) in the centimeter or millimeter range, in particular in the submillimeter range, in conjunction with high reliability of this position measurement (low measurement uncertainty). The geodesic measuring device furthermore has an angle measuring functionality for acquiring, with high precision, the alignment of the aiming axis, and a control unit for controlling the angle measuring functionality and the thermal imaging camera, and in particular the alignment of the sighting unit. According to the invention, in a thermal image measurement mode as a result of the initiation of a measurement process, position data of the sighted target point which are determined in this case, together with temperature information read out from the thermal image for the target point sighted using the aiming axis, are linked to one another in pairs in such a way that they can be called up in a manner associated with one another, in particular wherein the position data of the target point are stored in a manner correlated with the temperature information. In this case, the respective determined position data of the sighted target point are linked to the respective temperature information for the target point. 
     According to a method according to the invention, a target point on the target object acquired in the thermal image can be measured in a georeferencing manner, in particular automatically, on the basis of a temperature measurement criterion predefined depending on the temperature information which can be read out from the thermal image, wherein the optical aiming axis of the measuring device is aligned with the target point. In order to define the temperature measurement criterion, the temperature information in the thermal image can be converted, in particular by means of image processing, into areas each representing a temperature range, wherein the areas are delimited with respect to one another by isotherms, and/or a center of a temperature range, in particular an area centroid, can be determined. By means of the temperature measurement criterion, it is possible to determine temperature information for a measurement process in such a way that those positions which correspond to the temperature information determined can be measured automatically on the basis of the temperature measurement criterion thus defined. In this context, the measurement laser beam can be automatically aligned with the respective positions and the corresponding points can thus be measured. 
     By means of such image processing, a recorded temperature profile which varies in color continuously in accordance with a temperature gradient or slope can be subdivided into individual zones, wherein each of these zones represents a previously determined temperature range, e.g. from +10° C. to +15° C. The temperature ranges can be adapted in accordance with the temperature difference from the largest measured temperature to the smallest measured temperature. In the case of large temperature differences, for example, larger ranges can be defined in order that the number of ranges determined on the basis of an image can be kept manageable; conversely, in the case of an overall small temperature difference, the temperature range for a zone can likewise be chosen to be small, in order that differentiations of ranges can thus be effected. 
     On the basis of the zones thus derived, a boundary line between two zones can in turn be determined by means of image processing. Said boundary line then simultaneously embodies a line which, along its course, can represent a constant temperature on an object. Along these derived isotherms, a measurement can take place and the limit of a temperature range can thus be determined exactly. In addition to determining delimiting isotherms, it is also possible to derive centers of the zones, which correspond e.g. to the area centroid and thus simultaneously represent the central point of said zone. The determination of a position of a source of a heat leak can be carried out by means of this calculation. Thus, by way of example, it is possible to localize leakages on heat-carrying lines and subsequently to implement measures for sealing or to locate further heat sources. 
     In particular, with a method according to the invention, measurement can be effected along a path representing predetermined temperature information or a temperature profile, in particular along the isotherms, and/or constantly with respect to a point of the predetermined temperature information, in particular with respect to the center of the temperature range. 
     As a result, it is possible to determine not just individual points appropriately and positionally, rather it is possible to carry out a precise determination and measurement of extensive objects whose properties correspond to a predetermined (temperature) criterion. Thus, by way of example, it is possible to measure a region or point in which a temperature conspicuousness is present and this region can be processed on the basis of the position information determined in this case. Alternatively or additionally, it is possible to track not only a spatial profile of a temperature criterion, but also a temporal profile. In other words, it is possible e.g. constantly to carry out measurements with respect to predefined points and firstly to track a possible change in the spatial position of said points and/or secondly to record a change in temperature and the temporal profile of this change at said points. Consequently, at least these two cases of observation can be relevant. Thus, firstly it is possible to acquire and observe the temperature and/or its change or its temporal profile on a spatially defined point; secondly, it is possible to predefine a defined temperature and to constantly determine the position of a point or region having said temperature. By means of this possibility, it is possible to observe objects over a long period of time and to detect changes in their structure and/or in their thermal properties. A temporally extensive observation duration can be used in particular for monitoring large structures, such as e.g. a dam, and contribute to fulfilling safety conditions. 
     In addition, with a method according to the invention, measurement can be effected automatically with a predetermined point-to-point resolution and/or with a predetermined temporal separation of individual measurements. It is thereby possible to vary the desired or required precision of dimensions and positions to be acquired and a measurement duration associated therewith. Thus, both the center of a temperature zone and the delimitation thereof by an isotherm can be measured with appropriate precision and, on the basis of these measurement data, e.g. constructional work or repair measures can be carried out positionally precisely on an object. By way of example, for this purpose it is possible to detect between 5 and 50 points over a distance of 10 cm along a line. Alternatively, a resolution can also be defined in a manner dependent on an angle change; thus, it is possible to measure e.g. 10-100 points during a change in the detection angle of 10°. With regard to the temporal detection, by way of example 1-60 measurements can be effected per minute. 
     In the context of a method according to the invention, furthermore a reference beam can be guided along a reference path, wherein, during the guidance of the reference beam, at least one part of the reference path is perceptible on the object as a reference line visually and/or by means of a detector and the reference beam is guided on the basis of the temperature measurement criterion, in particular along the isotherms. 
     Such a method, carried out e.g. by means of a total station, can afford further advantages for the user and whoever plans furthermore to carry out activities on the basis of the position information generated. Thus, positions determined beforehand on the basis of an acquired image of an object can be marked. For the marking of the position, a laser beam visible to the human eye can be projected onto one of the measured points and thus indicate e.g. a heat source. By guiding the visible beam along a derived isotherm, it is furthermore possible to identify an extensive area region, when this identification can be maintained in particular for the duration of a possible technical activity or for marking out the region determined. With the use of a laser beam that is not visually perceptible, a detector can be used to find the marking laser beam and to determine the course thereof. 
     In a method according to the invention, the temperature information and a corresponding daylight image can be represented independently of one another and/or at least partly in a superimposed manner, in particular wherein the temperature information and/or position information with respect to points can be transmitted to a controller. Furthermore, the distances and angles with respect to points can be referenced and linked to a local coordinate system. 
     A superimposition or a juxtaposed representation of the thermal image and of a daylight image corresponding thereto can contribute to an unambiguous identification of points to be measured within the visual range of the two images. By way of example, if an unambiguous differentiation of points cannot be reliably carried out solely on the basis of the thermal image, then a daylight image that captures the same visual range as the thermal image can be consulted for differentiation and the differentiation can thereby be made possible. By superimposing the two images it is possible—depending on the respective measurement environment—, in contrast to a representation of the images next to one another, for the unambiguity with regard to a differentiation of points to be increased further. Thermal and daylight images can be captured by means of one camera or one sensor, which can realize recordings in both spectral ranges, or by means of two different sensors. The controller generally allows the user to operate a total station by remote control. By means of the transmission of the image information acquired by the camera, in particular in real time, the user can use the specific temperature information for aligning the total station by remote control and for measuring points. 
     Furthermore, with a method according to the invention, the coordinates with respect to a target point on the target object can be determined and extracted and the coordinates are transmitted into a computer unit, in particular into a CAD system, wherein measurements of distances and angles in the acquired thermal image can be carried out on the basis of the coordinates. In this case, the coordinates can represent positions by indications of degrees of longitude and latitude, wherein additional altitude information with respect to the positions can be present. The position data generated in the measurement process can be linked to the thermal and/or daylight image information and both be processed further directly on the measuring device and be transmitted to a further computer system. The linkage created makes it possible to carry out a determination of e.g. distances, surface areas, temperatures on objects or temperature profiles, without having to carry out further measurement processes. Furthermore, with respect to each acquired image of the measuring device, at the same time an acquisition direction can be concomitantly acquired and in particular linked to and stored with the acquired image. Using this direction information, a point on a previously acquired image can be selected and declared as “to be measured” such that the measuring device can automatically move in the concomitantly acquired acquisition direction and measure the selected point. 
     A geodesic measuring device according to the invention, in particular a total station or a theodolite, for determining position data of a target point on a target object comprises a sighting device, in particular a telescopic sight, wherein the sighting device is pivotable relative to a base of the measuring device in order to change the alignment thereof and at least has an objective unit that defines an optical aiming axis, an electronic distance measuring unit, and a thermal imaging camera for acquiring a thermal image, in the direction of the optical aiming axis. Furthermore, an angle measuring functionality for acquiring, with high precision, the alignment of the aiming axis, and a control unit for controlling the angle measuring functionality and the thermal imaging camera, and in particular the alignment of the sighting unit, are provided. According to the invention, in the context of a thermal image measurement mode under the control of the control unit, as a result of the initiation of a measurement process, the position data of the sighted target point, together with temperature information whose position on the thermal image corresponds to a position of the target point that is defined by the alignment of the optical aiming axis, are linked to one another in pairs in such a way that they can be called up in a manner associated with one another, in particular wherein the position data are stored in a manner correlated with the temperature information by storage means. 
     Furthermore, a geodesic measuring device according to the invention, in particular comprising means for image processing, can be embodied in such a way that the measuring device has a control functionality, wherein, in the context of the control functionality, an abovementioned method according to the invention for determining, with geodesic precision, the position of a target point on a target object is performed, in particular automatically. The measuring device can furthermore have means for image processing and/or a source of electromagnetic radiation, in particular a laser beam source, for generating a reference beam and guide means for guiding the reference beam along a reference path, and the control functionality can be designed in such a way that, when the control functionality is performed, one of the abovementioned methods according to the invention is performed. 
     With a geodesic measuring device according to the invention, as a result of the initiation of the measurement process, a georeferencing measurement—controlled by the control unit—with respect to a target point on the target object acquired in the thermal image can be effected, in particular automatically, on the basis of a predefined temperature measurement criterion, wherein the optical aiming axis of the measuring device is aligned with the target point. In this case, the measurement can be effected on the basis of a thermal image conditioned by means of image processing. In order to define the temperature measurement criterion, it is possible to carry out a conversion of the temperature information into areas each representing a temperature range, wherein the areas are delimited with respect to one another by isotherms, and/or a determination of a center of a temperature range, in particular of an area centroid, by image processing means. 
     According to the invention, the measurement can be effected along a path representing predetermined temperature information or a defined temperature profile, in particular along an isotherm, and/or constantly with respect to a point of the predetermined temperature information, in particular with respect to a center of a temperature range. 
     On a geodesic measuring device according to the invention, the control unit can furthermore be designed in such a way that the measurement is effected automatically with a predetermined point-to-point resolution and/or with a predetermined temporal separation of individual measurements. 
     Furthermore, the inventive geodesic measuring device can have a source of electromagnetic radiation, in particular a laser beam source, for generating a reference beam and guide means for guiding the reference beam along a reference path, wherein during the guidance of the reference beam, at least one part of the reference path is perceptible on the object as a reference line visually and/or by means of a detector and the reference beam is guided on the basis of the temperature measurement criterion, in particular along an isotherm. Moreover, a temperature-specific point, in particular the center of the temperature range, can be marked by means of the reference beam. 
     The inventive geodesic measuring device can have an output unit, in particular a display, wherein the temperature information and a corresponding daylight image can be represented independently of one another and/or in a manner at least partly superimposed on the output unit. In particular, with a geodesic measuring device according to the invention, acquired data and/or information can be communicated to a controller, wherein output means for representing the acquired data and/or the information, in particular the temperature information, are provided at the controller. 
     Furthermore, with a geodesic measuring device according to the invention, coordinates with respect to the target point on the target object can be determined and extracted and the coordinates can be transmitted into a computer unit, in particular into a CAD system, wherein measurements of distances and angles in the acquired thermal image can be carried out on the basis of the coordinates. 
     On a measuring device according to the invention, such as e.g. a theodolite or a total station, a camera is arranged, which can be used to acquire images of an environment, wherein the acquired images are in each case related to a measuring direction of the total station. As a result, it is possible to select a point to be measured on an image and then to measure its exact position using distance and angle measuring means. For selecting the point, an acquired image can be conditioned by means of image processing. On a corresponding measuring device, alignment means, e.g. servo or stepper motors, can furthermore be provided, with which the alignment of the measuring direction can be set and by means of the control of which a measurement based on an acquired image can be performed automatically. Instead of a camera whose spectral range corresponds to that of the human eye, alternatively or else additionally it is possible to provide a thermographic camera or a thermal imaging camera which has a spectral detection range which is wider or shifted in the spectrum and thus makes optical ranges that are inaccessible to the human eye accessible in a mediated manner and can acquire e.g. temperature information in the infrared range (and thus indirectly energetic properties of objects). Such a camera can be embodied such that it can capture both a daylight image and a thermographic image and can make available the image information in each case—represented by electronic signals—either individually or in a combined or superimposed manner. 
     With such a measuring device, therefore, firstly an object can be captured by the camera such that an image which arises as a result corresponds to the visually perceptible range of the human eye. In addition to this image, a further image can be created by a recording in the infrared range. Both images can be displayed to a user individually, together next to one another or at least partly in a superimposed manner on a display provided on the measuring device or on the total station. In addition, data or forms extracted from a thermal image can also be superimposed with the daylight image. Alternatively or additionally, one or both images can also be represented on a remote control or a controller with display, which is connected to the measuring device, in particular in a wireless manner via radio. This display can furthermore be embodied as a touch-sensitive “touch display” and thus simultaneously serve as input means for the user alongside other input means possibly present, such as e.g. a keyboard. 
     On the basis of a displayed image, the user can select a point in an environment captured on the image and can determine the position data with respect to said point by measurement. On the basis of a thermographic image, more extensive possibilities during object measurement can be made available to the user. Temperature information, usually represented by a color gradation, can be graphically visualized on such a thermal image. A temperature profile can usually be represented thereon in such a way that a wavelength which is detected in the spectral range and which corresponds e.g. to a comparatively low temperature of an object is represented in a blue-violet color and regions on objects having a high temperature are correspondingly represented as reddish. Between these limits of the detectable spectral range, object temperatures are represented in accordance with a previously defined color profile. 
     By way of example, a temperature distribution of an object, e.g. of a house, can thus be represented with a color gradation in order to provide information about which parts of the object are heated to a greater extent and possibly emit more heat to the environment than other colder parts. Such information enables the user for example to identify a heat leak or to investigate the quality of an insulation. After a leak has been visually located, the position of the leak can then subsequently be moved to and measured exactly by means of the angle and distance measuring unit of the total station. From energetic standpoints, in particular, this combination of visual detection process and geodesic measurement process for temperature zones affords a very good possibility for identifying and determining the position of instances of temperature conspicuousness and implementing measures on the basis thereof. By way of example, it is thus possible to determine locations or positions at which an insulation of a building does not comply with generally required standards. The deficient insulation can then be repaired effectively and with pinpoint precision. 
     Furthermore, the spectral detection range of a thermal imaging camera can differ e.g. from the detection range of the human eye with regard to the reflection property of radiation on objects. As a result, by means of a thermal imaging camera, different object properties can be acquired by detecting reflections, in particular reflections of electromagnetic radiation having a wavelength which is in the detection range of the camera, wherein the temperature of the object can be constant as much as possible over the extent thereof. On the basis of such reflection properties, a measurement with respect to a target point thus identified can in turn be effected. 
     A measuring device according to the invention can furthermore also be used effectively in an environment that appears dark to the human eye. The thermal radiation emerging from objects can be detected even in darkness, wherein points can be selected and measured on the basis of the images thus recorded. Such a use proves to be advantageous particularly under difficult lighting conditions e.g. underground or when constructing road or railroad tunnels. Intensive artificial illumination of the measurement environment can thus be dispensed with in part. Particularly when a natural terrain does not have to serve as target object, but rather target marks are used which possibly have a thermal signature, a total station according to the invention comprising an infrared or thermographic camera can be used in an environment that is absolutely devoid of light. 
     In particular, the detector of a geodesic measuring device according to the invention can detect a thermally coded target mark, wherein a detection direction of the measuring device can be constantly aligned with the target mark by means of alignment means for aligning the measuring device. By means of a total station corresponding to the invention, it is thus possible to carry out sighting and tracking of one or a plurality of thermally coded, e.g. heated in a defined manner, targets. By means of different codings, in particular by means of different temperatures of the targets, a plurality of target marks can be identified and differentiated from one another. Such target marks can furthermore be assigned to previously determined machines or objects and it is then possible to determine these objects with tracking of the respective targets e.g. in a manner controlled with positional precision or the positions thereof, in particular also constantly. In this case, the measuring device can be aligned with the target mark constantly, e.g. by means of actuating, stepper or servo motors, in particular continuously, such that the detection direction of the device points directly in the direction of the target mark. 
     A system according to the invention comprises a measuring device according to the invention and a target mark, wherein the target mark has a predetermined thermal coding, in particular a region of defined temperature and/or a defined geometric arrangement of temperature-regulated regions, wherein a position of the target mark on the thermal image acquired by the thermal imaging camera is determinable by means of an identification of the thermal coding, in particular by image processing. By means of such a target identification functionality, a target mark or target assigned to a machine, for example, can be determined positionally precisely and the position of the machine can thus be derived. For this purpose, at least part of the target mark can be heated to a defined temperature. 
     In addition, by means of the system according to the invention, in the context of target tracking, the position of the target mark on the thermal image can be assigned to the direction of the optical aiming axis of the measuring device and the control unit can be designed for controlling the alignment of the sighting unit in such a way that the optical aiming axis is constantly aligned with the target mark. With this alignment, a target provided with a target mark can be tracked. By way of example, the position of a construction machine in the terrain can be continuously ascertained. 
     Furthermore, the target mark for use with the system according to the invention can have a temperature-regulating unit for the thermal coding of at least one part of the target mark. 
     A further aspect of the invention is a method for determining the position of a target point with a target mark using a geodesic measuring device with a thermal imaging camera, wherein the target mark is thermally coded in a defined manner and the position of the target mark on the acquired thermal image is determined. 
     In this case, the position of the target mark on the thermal image can be assigned to the direction of the optical aiming axis of the measuring device and the aiming axis can be constantly aligned with the target mark. In addition, the target mark can have an at least partial thermal coding. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The method according to the invention and the device according to the invention are described in greater detail purely by way of example below on the basis of concrete exemplary embodiments illustrated schematically in the drawings, and further advantages of the invention will also be discussed. Specifically in the figures: 
         FIG. 1  shows a measuring device according to the invention with a thermal imaging camera; 
         FIG. 2  shows a thermal image recorded on an object surface with a measuring device according to the invention; 
         FIG. 3  shows a temperature profile with a localized heat source; 
         FIGS. 4 a - b    show subdivisions of a temperature profile of a thermal image into different heat zones; 
         FIG. 5  shows a daylight and a thermal image recording of a building with a measuring device according to the invention; 
         FIG. 6  shows a construction machine with a thermally coded target mark and a measuring device according to the invention; 
         FIG. 7  shows a terrain with thermally coded target marks and a measuring device according to the invention; 
         FIG. 8  shows two measuring rods each having a reflector and thermal coding elements. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a measuring device  1  according to the invention with an integrated detector  2 , which can be embodied in particular as a thermal imaging camera, wherein the detector  2  has a detection direction as much as possible parallel to a sighting direction of a sighting device  4 , likewise arranged in the measuring device. Furthermore, the measuring device is provided with an output unit  3 , in particular with a display, on which images  10  acquired by the camera  2  can be represented. Moreover, the device has two mutually perpendicular rotation axes  5   a ,  5   b  for alignment with an object. The measuring device, e.g. a total station, can thus be aligned with an object by means of the rotation of the sighting device  4  about the two axes  5   a ,  5   b  and can firstly acquire an image  10  of said object, in particular with temperature information. From the image, a temperature profile of the object can subsequently be derived and temperature zones defined by means of image processing can be determined. Afterward, points of interest, e.g. points with instances of temperature conspicuousness, can be measured with the aid of the sighting device  4  and their position on the object can be determined exactly. 
       FIG. 2  shows a measuring device  1  according to the invention and an object  15 , or the object surface thereof, a thermal image  10  of which is acquired. On the object  15  itself, a temperature profile  9  corresponding to the thermal image  10  is shown for the purpose of better illustration. In a spectral range accessible to the human eye, the object surface would appear as a homogenous area without conspicuous features. However, by extending the spectral range that can be perceived and displayed, it is possible for further properties of said surface to be visualized. The temperature profile corresponds to a representation after image processing performed on a continuous temperature profile. The formerly continuous (color) profile is subdivided, by image processing means at the measuring device, into the zones or ranges  11   a - e , each representing a predefined temperature range. The temperature ranges  11   a - e  are in turn delimited from one another by in each case a boundary line  12  representing a specific temperature. By way of example, such an isotherm  12  is illustrated between the ranges  11   a  and  11   b . A temperature range embodied by the temperature zone  11   b  can extend for example from 35° C. to 30° C., wherein a temperature of 30° C. is then present along the isotherm  12  and the temperature zone  11   a  represents the temperature range of e.g. 30° C. to 25° C. Outside the zone  11   a , a temperature of less than 25° C. can then prevail and is not detected any further in accordance with the detection settings of the thermal imaging camera  2 . By means of the sighting device  4  arranged in the measuring device  1 , furthermore, the position and the delimitation of a temperature range of interest on the object  15  can be measured exactly and, in a next step, be extracted into a CAD model and be transferred together with the object  15  into a coordinate system. For this purpose, a measurement beam  30  is guided e.g. along the isotherm  12  determined in the image  10  and the distance with respect to the object  15  is determined constantly with a predetermined point-to-point resolution. In this case, the measurement beam  30  can be guided automatically, in particular. 
       FIG. 3  shows the temperature profile  9  from  FIG. 2 , wherein the classification of the temperature profile into temperature ranges  11   a - e  has likewise already been effected by means of image processing. The temperatures of the temperature zones  11   a - e  increase toward the center, that is to say that the zone  11   a  has a temperature range having lower temperatures than the zone  11   e , representing the range having the highest temperatures. By means of image processing, furthermore, the center  13  of the temperature profile can be determined and e.g. a heat or cold source can thus be localized. Likewise, it is possible to define straight lines  14   a ,  14   b  which run along a temperature gradient and run through the center  13  of the temperature profile. As a result, it is possible e.g. to perform a measurement along the straight lines  14   a ,  14   b  and to localize thereon points having the lowest and simultaneously points having the highest detected temperatures. It is thus possible to make statements about the temperature profile or the extent of one of the plurality of temperature ranges  11   a - e , wherein it is not necessary to measure the entire spatially detected temperature range  11   a - e , rather it suffices to measure e.g. two mutually perpendicular straight lines  14   a ,  14   b  which intersect at the center  13 . 
       FIGS. 4 a  and 4 b    each show an exemplary subdivision of a temperature profile  9  into temperature or thermal ranges  11   a - g . In this case, the entire detected temperature range in  FIG. 4 a    is subdivided into seven sub-ranges  11   a - g , wherein the temperature range in  FIG. 4 b    is subdivided only into two sub-ranges  11   a - b . Such a different subdivision of a temperature range can make the desired information clear, depending on the requirement. If e.g. a temperature profile  9  is detected which encompasses a relatively small temperature difference of e.g. in total 0.5° C., then a subdivision of this total profile into a plurality of sub-ranges can make it possible to carry out a differentiation and a classification of temperature ranges. By contrast, particularly when evaluating a temperature profile which encompasses a relatively large temperature range of e.g. 100° C. temperature difference, said profile can be represented in a manner gradated in fewer ranges in order here, too, to be able to perform a meaningful differentiation of temperature zones. 
       FIG. 5  shows three images  20   a - c  of a building and a measuring device  1  according to the invention, which can be used to acquire said images. The first image  20   a  shows a daylight recording of the building, wherein this recording can be acquired both by means of a camera assigned to the measuring device  1  and having a spectral detection range corresponding to the human eye, and by means of a spectrally extended thermal sensor at the measuring device, in particular by means of a thermal imaging camera. The edges  21  of the building, a window  22  and a chimney  23  are visible on the image  20   a . In the second image  20   b , by contrast, sharp edges  21  of the building are no longer visible, rather the temperature distribution over the front of the building is represented. This image  20   b  may have been acquired by a thermal imaging camera in the infrared spectral range. The regions of the building which are represented darker are clearly discernible, which substantially run along the edges  21  of the building, around the window  22  and in the region of the chimney  23  and indicate regions in which a greater thermal emission is present. In addition, a temperature conspicuousness  24  can be visualized in the thermal image recording  20   b . Said temperature conspicuousness  24  can indicate that at this location e.g. a heat leak, caused for example by a defective building insulation, is present at the building. The heat leak  24  can be measured on the basis of the image information by means of the measuring device  1  and the position with respect to the building can be determined exactly. For this purpose, a measurement beam  30  can be guided along previously derived isotherms and can measure the latter with a defined resolution. By extracting isotherms, it is possible to determine a core region of the temperature conspicuousness  24  and to transfer it into a common coordinate system together with the building coordinates. The precise position of the leak  24  relative to the building can thus be represented with the aid of a CAD model. Furthermore, a further image  20   c  can be generated, which shows the building contours visible from the daylight image  20   a  together with the heat leak  24 . By superimposing the information derived from the two images  20   a  and  20   b , the position of the temperature conspicuousness  24  can be represented exactly and visually marked by means of a, more particularly visible, laser beam by the beam being guided along a reference path corresponding to the delimitation of the core region of the heat leak  24 . Such a marking can serve for orientation e.g. for repair work for eliminating the heat leak  24 . 
       FIG. 6  shows a measuring device  1  according to the invention and a construction machine  25  in the terrain  28 . The construction machine  25  has a target mark  26 , which can be sighted by the measuring device  1  by means of a measurement beam  30 . According to the invention, the target mark  26  can furthermore be thermally coded, that is to say that the target mark  26  can be heated at least partly to a predefined temperature, for example to a defined value of between 50° and 100° C., or be cooled for example to a defined value of between 5° C. and 20° C., such that a thermal radiation defined thereby emerges from the target mark  26 . In particular, the temperature can be chosen in such a way that a clear differentiation of temperature-regulated objects from the environment is possible. Thus, depending on the outside temperature or ambient temperature, a temperature or temperature range suitable for the respective requirements can be chosen or predefined for the target mark  26 . By way of example, given a prevailing air temperature of 40° C. and sunshine, a temperature range of 100° C. to 110° C. may be suitable for the target mark  26 , and a target mark  26  temperature-regulated to 30° C. may be suitable at −20° C. The measuring device  1  once again has a thermal imaging camera which can be used to capture the construction machine  25  and thus simultaneously the target mark  26  that is temperature-regulated in a known and defined manner. By means of image processing, in the measuring device  1 , the temperature of the target mark  26  can be determined and the position thereof with respect to the detection direction of the camera or with respect to the sighting direction of the sighting unit can be derived. By means of the predefined temperature of the target mark  26 , the target mark  26  captured in the thermal image can be identified at the measuring device  1  according to the invention and, with the assignment of the target mark  26  to a construction machine  25 , the position of the construction machine  25  can be determined unambiguously. 
     For an initializing identification of a target mark  26 , an initialization can be effected by the target mark  26  that is temperature-regulated in a defined manner being recorded by means of the thermal imaging camera and, from the recorded image, a temperature or a temperature range for the target mark  26  can be derived and stored. In this case, the temperature regulation of the target mark  26  or of parts thereof can be produced and maintained by means of a radiant heater assigned to the target mark. As an alternative thereto, the target mark  26  can be heated to a specific predefined temperature and a temperature conspicuousness corresponding to that predefined temperature can be sought by means of image processing on an acquired thermal image on the part of the measuring device  1 . 
       FIG. 7  shows how a plurality of differently temperature-regulated target marks  26   a - e  can be simultaneously assigned to a plurality of objects. In this case, the marks  26   a  and  26   b  are respectively assigned to a construction machine  25   a  and  25   b . By means of a constant image analysis of a thermal image acquired at the measuring station  1  according to the invention and subsequent image processing, the movements of the target marks  26   a  and  26   b  and thus the movement of the construction machines  25   a  and  25   b  can be concomitantly tracked in the acquired image and, on the basis thereof, a compensating alignment of the measuring station  1  in the direction of the target marks  26   a  and  26   b  can be effected. By means of the different thermal coding of the marks  26   a  and  26   b , the latter can be rapidly differentiated from one another and the sighting direction of the measuring device  1  can thus be aligned rapidly and precisely with the respective target mark  26   a ,  26   b  and a precise determination of the position of the construction machine  25   a ,  25   b  can be carried out. In addition to the target marks  26   a  and  26   b  on the construction machines  25   a  and  25   b , further target marks  26   c - e  are positioned in the terrain  28 . In this case, the two marks  26   c  and  26   e  are arranged at a respective measurement point in the terrain  28  and on the building shown. By virtue of the fact that these two target marks  26   c  and  26   e  in turn appear different on an acquired thermal image, the corresponding targets can be rapidly differentiated from the others, the measuring station can be aligned with them and their position can be determined exactly. A further target mark  26   d  shown is arranged on a measuring rod  41  guided by a user. The target mark  26   d  that is temperature-regulated in a defined manner can in turn be identified on the part of the measuring station  1  unambiguously by means of the processing of an acquired thermal image, on which the target mark  26   d  is concomitantly captured, and of the temperature characteristic recorded therein. On the basis of a direction with respect to the target derived therefrom and with knowledge of the distance roughly at which the target is situated and the spatial relationship between the temperature-regulated target mark  26   d  and a reflector  41  on the measuring rod  40 , that is to say the distance between the target mark  26   d  and the reflector  41 , the reflector  41  can be sighted directly by the sighting unit of the measuring station  1  and the precise position of the measuring rod can thus be determined. In addition, the position of the measuring rod  40  can be constantly determined on the basis of the temperature-regulated target mark  26   d  by means of image acquisition and image evaluation and the targeting device of the measuring station  1  can be aligned with the reflector  41 , e.g. a prism. The user of this measuring system according to the invention is thus enabled to pace out different measurement points and to detect the respective positions of the points rapidly and automatically. 
       FIG. 8  shows two measuring rods  42  each having a reflector  41 , which can be configured e.g. as a prism. Furthermore, a coding element  29  is in each case arranged on the measuring rods  42 , said coding element extending over part of the measuring rod  42 . On the coding elements  29 , by way of example, two different forms of a coding  27   a  and  27   b  applied thereon are shown. The coding forms  27   a  and  27   b  in this case each show dark regions on the coding elements  29  which can be temperature-regulated in a defined manner and can thus have a defined thermal coding partially or areally in specific forms  27   a  and  27   b . By way of example, three thermal struts  27   b  or a rectangular area  27   a  or other geometrical figures can be provided on the coding elements  29 . Using these different coding forms  27   a  and  27   b , it is possible e.g. to facilitate a differentiation of target marks on a thermal image by means of image processing. An identification can then take place no longer solely on the basis of different temperatures of the target marks, but rather additionally (or alternatively) by means of the identification of the form  27   a  and  27   b  of the temperature-regulated regions. The target mark identified in a recorded thermal image on the basis of the defined temperature and/or form  27   a ,  27   b  thereof can be used together with its position in the thermal image in various ways. Firstly, an automatic target tracking of the identified target mark can be effected and in this case the sighting direction of the measuring station  1  can be constantly aligned with the target mark. Such a target tracking on the basis of a daylight image is described e.g. in EP 2 141 450. In this case, the measuring station is automatically aligned with a target and tracks the latter, wherein the target identification is effected by means of image processing of a previously acquired image of the environment. This system supports a target tracking and target acquisition by means of a laser beam directed onto a reflector and detected at the measuring device, in particular when the laser beam lies outside a detection range and a target tracking cannot be realized solely on the basis of the detection of a laser reflection. 
     According to the invention, for the purpose of target tracking, a thermal image of a terrain or of an environment can be acquired, in particular constantly, and a target mark that is temperature-regulated in a defined manner can be identified therein by means of image processing and a target can be tracked by means of an automatic and constant alignment of the measuring station according to the invention with the target mark or in accordance with a movement of the target mark in the thermal image. Such a target identification and tracking can be used in particular for supporting an automatic laser target tracking unit. By virtue of the additional use of thermal image information, a target to be sighted, e.g. in the case of an interruption of the laser light path, can thus be rapidly acquired anew. 
     Furthermore, a manual or automatic target seeking can take place on the basis of the temperature identification of the target mark by means of image processing on an acquired thermal image. In addition, by means of the position of the target mark identified in the thermal image, high-precision sighting of a target can take place automatically. For this purpose, firstly, by means of image processing on the basis of a temperature that is different with respect to the environment and/or on the basis of the geometrical form of the thermal coding, the position of a thermal coding element  29  can be determined exactly. For a high-precision sighting e.g. of a prism that is based thereon, the distance between the thermal coding and the reflector  41  may be known. This additional information makes it possible for the sighting unit of the measuring station to be aligned with the reflector directly manually or automatically and for the position thereof to be determined exactly.