Abstract:
In geodetic measuring systems and measuring devices ( 14 ) there exists a need to find and detect, rapidly and automatically, marker points to be measured that are provided with a marker (retro reflector) ( 2   a ). For the rapid detection, identification and determination of the horizontal angles of such a marker, even at greater distances, electromagnetic radiation in the form of a vertical fan ( 17 ) is transmitted by a transmitter unit ( 1 ) whose radiation is received, after reflection from the marker, by a receiving unit with a view field in the form of a vertical fan. By analyzing the signal strength and the apparent object size, a plausibility test and a reliable suppression of foreign or interference markers can be achieved. Such a marker searching device is marked by a selective analysis of specific characteristics of a marker detected. On the basis of the plausibility test, a rapid, certain and robust location of markers is possible.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates generally to surveying and geodetic measurements, and relates more particularly to a process and device for the automatic location of a reference marker, a receiver unit, a geodetic measuring device, and geodetic measurement systems.  
           [0003]    2. Description of the Relevant Art  
           [0004]    For a long time, there has existed the need, in connection with geodetic measurements, for automatically recognizing geodetic reference markers to be measured and located in the field, and, if possible, at the same time, obtaining a rough measurement. This necessity is even greater as a result of the tendency toward fully automatic integrated measuring systems.  
           [0005]    Optical-electronic devices for the automatic location of geodetic reference markers or a retro reflector or a reflection foil are corresponding already used in various embodiments. Devices of this type thereby supplement the usual sensory measuring means usually employed in geodetic measuring work. The combination of a motorized theodolite with automatic marker detection provides substantial advantages.  
           [0006]    Devices for finding markers and, therefore, also the present invention involve all measuring devices that are optically pointed to measuring points through directing means handled by humans.  
           [0007]    The concept “geodetic measuring device” in this connection should generally be understood to be a measuring instrument that has devices for measuring or checking data with spatial references or also for pointing. Especially, this involves the measurement of distances and/or directions or the angles to a reference or measuring point. In addition, however, additional devices, for example, components for satellite-supported location determination (for example, GPS or GLONASS) may be present, which can be used for measurements in accordance with the invention. Here, geodetic measuring devices should be understood to mean theodolites, level or total stations, tachymeters with electronic angle measurements, and electronic optical distance measuring devices. Similarly, the device is suitable for use in specialized devices with similar functionality, for example, in military aiming circles or in industrial construction or process monitoring. These systems are thereby also included under the concept “geodetic measuring device.” 
           [0008]    Automated theodolites commonly used today, as an example of a geodetic measuring device, are not only equipped with angle and distance sensors, but also with an optical-electronic marker seeking positioning and marker point measuring device, hereinafter called automatic marker locating unit (AZE). Such theodolites are capable of moving directly to the marking point and measuring the spatial coordinates. When operating perfectly, the time saved with such automated instruments is substantial. If, in addition, the system can be operated through remote control, for example, from the marking point as a one-man station, then the work efficiency and the savings in cost achieved thereby is even greater.  
           [0009]    An essential component of these automated measuring instruments is AZE. Various solutions are known, such as CCD or CMOS cameras with image processing, optical-electronic position-sensitive semiconductor detectors (PSD); 4-quadrant diodes, acoustical-optical beam scanners, etc.  
           [0010]    The primary function of this AZE includes the exact measurement of a reference mark or a reflector precise to the millimeter, over short and long distances, where distances in excess of 1000 m can also be measured. In order to achieve this mm precision, the seeking devices have the disadvantage of a limited sensor site view field. Only in the case of small to medium view fields of a few degrees can point precisions of &lt;5 mm be achieved at 1000 m.  
           [0011]    A substantial disadvantage of a small sensor view field is that the search for the marker is rendered more difficult, since the reference mark to be measured is often outside the view field at the beginning of a measurement. In many applications, especially in the short distance range, which does with a broad angle working field, an expanded sensor view field is advantageous.  
           [0012]    Today, two methods are used in searching for markers. In one method, the sensor seeks the marker independently following a programmed algorithm or procedure; however, this takes time, due to the small field of view. In the second method, the search field is defined by the user, so that marker search proceeds in a more directed manner and takes less time; however, this has the disadvantage that the search field configuration must be reprogrammed every time the position changes.  
           [0013]    A further disadvantage exists in following moved markers. In the case of tangential movements that are too rapid or jerky for the marker guidance of the automatic theodolite, it can occur that the marker leaves the view field of the marker detection device. Even a loss of the marker for a short time can then interfere with an efficient following process.  
           [0014]    Further deficiencies in the case of devices with AZE in the state of technology are also the lack of robustness in the recognition of markers in the case of reflections by foreign markers. Foreign markers are those with a high degree of reflectivity, such as traffic signs. In marker recognition, the identification of the marker to be measured has not to date been satisfactorily solved, since especially the lack of robustness in solar reflections on objects with shiny surfaces has a disadvantageous effect.  
           [0015]    While solar reflections on objects can be recognized with modern equipment, nevertheless the analysis necessary for this takes time, as a result of which the search process comes to a halt at every reflection.  
           [0016]    In the case of rough-search sensors of the state of technology, due to the small sensor view field, the rough marker search requires too much time. The small view field, therefore, has effects that are out of proportion. In the first place, it has a smaller area of coverage of the environment, so that examining the search range requires a longer period of time. Secondly, the coverage must be done with a slower scan speed due to the shorter time that the object remains in the view field. A fan shape for the detection area of the sensors is, in this regard, more suitable, however the view fields, made up of fan angles of typically 1 to 5 degrees, is still much to small.  
           [0017]    From the patent CH 676 042, a device is known with a fan-shaped transmitter and receiver, which is housed in a rotating measuring head. Light pulses are transmitted in a light fan from the transmitter unit; the reflected impulses are correspondingly evaluated with respect to angular information. However, this device has a substantial disadvantage of selecting not only the markers to be measured, but also outside interference objects. Such objects are, among other things, optically reflecting objects such as plate glass windows or traffic signs, and even sunlight reflected from motor vehicles.  
           [0018]    An extension of the above marker search device for the rough determination of the marker coordinates is described in CH 676 041. In this case, a combination with an optical-electronic device is made for fine measurement. The actual marker search device sets up two fans that are perpendicular to each other, with which the location of the marker point is measured roughly. The subsequent fine measurement can then be carried out with the second device without the marker search procedure. The disadvantage of this combination is also the lack of robustness with respect to an erroneous locking in on foreign objects.  
           [0019]    A further device is known from U.S. Pat. No. 6,046,800. A motorized theodolite, which is equipped with a sensor to detect the marker point coordinates, is revealed, consisting of one or two fan-shaped transmission bundles and two optical receiver channels. A special characteristic of this device consists of the fact that the optical axes of the transmitting channel and the two receivers lie triaxially in a single plane. This makes it possible to differentiate between normal reflecting and retro reflecting objects in a rotational or searching movement of the theodolite by evaluating the sequence over time of the two signals received. This method of pupil division on the receiver side, however, has the disadvantage that this differentiating characteristic exists only at short distances; in addition, the device is expensive, due to the two receiving channels.  
           [0020]    From patent DE 196 23 060, a geodetic device for rough marker search is also known. This device consists of an optical-electronic vertical angle searcher essentially formed as a scanner. Transmitted and received beams are rotated around a (second) horizontally placed motor-driven axis. The intended result is a great range that is achieved on the basis of the parallel collimated optical bundles; this property is, however, purchased with the disadvantage of the point-type and therefore sequential and time consuming probing of the space. In the search process, the rapid vertically rotating sensor beam is simultaneously rotated slowly in the horizontal direction. A further disadvantage is the need for a supplementary angle measuring system on the scanner axis for the rough determination of the vertical angle. On the other hand, if the space were searched with a fan-shaped optical measuring bundle, then only a one-dimensional rotational movement around an axis would be necessary.  
           [0021]    A substantial disadvantage of all previously known devices is the insufficient robustness against strongly reflecting foreign objects that can be mistakenly interpreted as marker objects, as well as interference with or at least the delay of the search process as a result of bright sunlight or reflections of the sun.  
           [0022]    In most cases, the search process is supported manually through voice radio or data radio. In the device described in document DE 197 334 91, an additional optical receiving unit attached to the market object is used to check whether the search beam of the theodolite is hitting the marker object. If the corresponding search signal is being received, then the marker object reports its identification to the theodolite using data radio. This solution, while robust, affects the ergonomics at the marker object.  
           [0023]    The problems to be solved by this invention consist of an improvement of the sensor devices defined above.  
           [0024]    In this regard, one problem consists of providing a geodetic measuring device for the rough search of the marker, which is suitable for locating and identifying, as rapidly as possible, marker objects and determining rough coordinates, and which has a shorter searching time with a range of up to 1000 m. The speed of the search for the marker is a main problem, since it demands a large sensor viewing field, which can be achieved by a corresponding wide fan angle. As fan angles become larger, however, the range decreases. The problem to be solved by the invention is therefore to achieve the range of geodetic applications and simultaneously a high search speed.  
           [0025]    A further problem consists of making possible a search process that is robust against foreign light and self-reflection at foreign markers. The search process, at the same time, cannot be delayed or interrupted by foreign markers with a high degree of reflection or by items with solar reflections. At the same time, the problem includes the simultaneous identification of the marker objects to be measured on the basis of suitable identification characteristics, even during the search process.  
         SUMMARY OF THE INVENTION  
         [0026]    These problems are solved in accordance with the present invention. This invention substantially concerns an optical-electronic marker search device consisting of a fan-shaped transmitting channel that irradiates the marker to be located, a fan-shaped receiving channel that receives light reflected from the marker object, a motorized measuring device, for example, a theodolite, which moves around one of the two axes during the search process, at least one electronic evaluating unit to determine the rough location of the marker point, signal strength of the reflected signal, the width of the marker object in the scanning direction, and the distance to the marker object. Optically, the duration of the reflected optical signal can also be determined.  
           [0027]    Both the planes of the two optical-electronic light fans and the axis of rotation of the theodolite (=scanning axis for the search procedure) are oriented parallel to each other. In the following, the concepts of the horizontal and vertical motion are to be understood in such a manner that the corresponding components and a corresponding movement are present in a movement. A horizontal movement of the transmitter unit can therefore especially also be achieved by a movement tilted toward the horizon.  
           [0028]    A powerful and sensorily sensitive running time measuring device serves as a marker search device. Suitable running time meters with pulse modulation have a great range and a short measuring time. The attainable optical transmission powered with pulse laser diodes only millimeters in size is over 100 Watts. This makes it possible to achieve the range required for geodetic applications even with fan-shaped spreading of the transmitted beam. During a search run, the running time meter is operated in the continuously measuring mode. In this regard, the transmitter sends out optical impulses at a rate in the kHz range. Since the device is run in the single-shot evaluation process, information concerning the scanned environment is available in the nanosecond to microsecond range. The pulses received are probed with a rapid AD converter, which provides an intensity image of the environment. At the same time, the pulses probed can, for example, be stored in a 2D memory and evaluated later or a first analysis may be made soon and the further evaluation based on these first results which, for example, can be a bringing together or concatenation of the pulses.  
           [0029]    The dimensioning of the optical transmitting fan is done in such a manner that it covers the environment typically to be measured in the vertical direction. The divergence in the direction perpendicular to the fan is preferably narrow, limited by diffraction.  
           [0030]    A search with a device in accordance with the invention provides, as an output, an intensity image of the environment searched. The two-dimensional intensity image can be evaluated after the scan is completed or even simultaneously or soon after the recording. Possible results of such an evaluation can be, for example intensity maxima of any marker objects, a time for finding the marker or the equivalent angles to the marker object, or the distance to the marker object.  
           [0031]    The robustness vis-à-vis solar reflecting surfaces and reflecting distant markers is improved or attained only by using the invention. Due to the strong laser pulse, solar reflecting surfaces are not visible in the two-dimension intensity image for two reasons. First of all, the laser radiation of the transmitters is of a narrow spectrum and a comparatively narrow interference filter in the reception process blocks the sunlight to a great extent. Secondly, the pulse lasers generate strong light flashes whose density of radiation is greater than that of solar reflections. Robustness against solar reflective surfaces is thereby achieved.  
           [0032]    The necessary robustness against foreign or interference markers is more difficult to achieve. At first, in the two-dimensional intensity image, in addition to the actual marker object to be located, there often appear further optically reflecting objects.  
           [0033]    In the near range under 10 m, the problem can be solved by a special biaxial arrangement of the two optical fans. Transmitter and receiver are biaxially next to each other, where the sideward displacement is perpendicular to the fans. The view fields of the transmitter and receiver do not overlap below 10 m as a result. Single reflecting objects, such as mirrors, are not seen in this distance range by the receiver, only retro reflecting marker objects with a sideward displacement of the reflected beam such as, for example, the triple prisms common to measuring work generate a measurable received signal. As a result of this, the robustness below 10 m is solved by the biaxial arrangement.  
           [0034]    At all other distances, the real marker objects must be identified from the objects included in the two-dimensional intensity image in accordance with the invention.  
           [0035]    Any marker object generates both a characteristic signal process and a characteristic width as a function of the distance. The identification of marker objects is therefore possible using two distance-related measurement curves. For the object distance measured in each case, the width of the object and the signal strength are checked to determine whether they are within the tolerance range of the marker object sought. Depending on concrete marking parameters and measuring conditions, it may be sufficient to perform only a comparison with respect to a limit value, for example, a comparison with the lower limit value with respect to the signal and with the upper limit value with respect to the object size.  
           [0036]    If, during a scan, a reflected object is irradiated, then the signal and the object width are continuously compared to the tolerance values loaded. As soon as the transmitter fan has completely covered an object and all measured values lie within the tolerance limits, a marker object is identified and found. Depending upon application, the search process is stopped at the point or the coordinates, optionally along with parameters such as signal and width, are stored and the search process is continued without interrupting the scan so that further marker objects can be sought and found.  
           [0037]    The case, which is entirely possible, that at certain fan settings multiple marker objects occur simultaneously at different distances can be handled without a problem on the basis of distance measurements.  
           [0038]    In many applications, immediately after the instrument setup, the entire environment is scanned. This generates a two-dimensional intensity image, which contains all strongly reflecting objects. The coordinates of the irrelevant market objects, such as interference and foreign markers, are calculated and stored. With the knowledge of the coordinates of all interfering objects and foreign markers, these can be blocked out of further search runs. As a result, this makes it possible to save additional searching time, since the objects irrelevant to the measuring task no longer exist from a sensory point of view.  
           [0039]    When a marker object is found, the distance and one direction coordinate are known. Next, the second spatial direction is measured. This is achieved according to the known search procedure with the automated marker locating unit (AZE) present in the theodolite. The AZE search and measurement procedure is very efficient and rapid in this case, since only 1-dimensional movement or travel is necessary. The combination of the two devices results in a further advantage. Since the AZE measures the position of the marker object precisely to angular seconds, at the end of the AZE search and measurement process the marker point coordinates are known not only roughly, but with geodetic precision in the millimeter to sub-millimeter range.  
           [0040]    The combination of the marker search device with an automatic marker locating unit (AZE), in accordance with the present invention, makes possible the complete and mm-precise determination of the 3D coordinates of marker objects.  
           [0041]    An essential property of the process and the device in accordance with the invention is the speed of the search process. A complicating factor lies in the large signal dynamic resulting from the geodetic distance range.  
           [0042]    In a device according to the invention, this problem is supported or solved by measures taken on the transmitter side. The high signal dynamic can be allowed for by transmitting multiple laser pulses of differing intensity. The signal dynamic is thereby divided onto transmitter and receiver. In the short-distance range, the receiver evaluates the weak pulses with lower amplitude in the long-distance range, the strong pulses with higher amplitude.  
           [0043]    A suitable application of the device in accordance with the invention is represented by modular integration in a motorized theodolite with automatic marker locating unit (AZE) according to patent U.S. Pat. No. 6,031,606.  
           [0044]    The process according to the invention as well as a device according to the invention and a geodetic measuring device according to the invention are described in greater detail in the following, on the basis of the sample embodiments schematically represented in the drawing, purely as an example.  
           [0045]    The features and advantages described in the specification are not all inclusive, and particularly, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification and claims hereof. Moreover, it. should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter, resort to the claims being necessary to determine such inventive subject matter.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0046]    [0046]FIGS. 1 a - b  are representations of the principles of two embodiments of the process and device of the present invention, with vertical fans and single as well as double pulse modulation.  
         [0047]    [0047]FIG. 2 is an extract from a two-dimensional intensity image of a marker object for a process in accordance with the present invention.  
         [0048]    [0048]FIG. 3 is a schematic representation of the application of a plausibility band (tolerance value table) for signal amplitude.  
         [0049]    [0049]FIG. 4 is a schematic representation of the use of a plausibility band (tolerance value table) for the apparent size of the object (object width).  
         [0050]    [0050]FIGS. 5 a - b  are representations of the differing conditions for the biaxial property of the transmitting unit and receiving unit for the transmitted beam that is preferably limited in diffraction with a retro reflector and with a singly reflecting object.  
         [0051]    [0051]FIGS. 6 a - c  are representations of various embodiments of the receiver unit according to the present invention, with a structured fan, a horizontal fan tuft, and a two-dimensionally structured view field.  
         [0052]    [0052]FIGS. 7 a - b  are perspective representations of an automated geodetic measuring device according to the invention, and the combination of the search process with AZE.  
         [0053]    [0053]FIG. 8 is a block schematic as an example for a circuit-side embodiment of the device according to the present invention.  
         [0054]    [0054]FIG. 9 is a perspective representation of the geodetic measuring system in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0055]    The drawings depict various preferred embodiments of the present invention for purposes of illustration only. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention described herein.  
         [0056]    [0056]FIGS. 1 a - b  show two possible embodiments of a device in accordance with the present invention to carry out the procedure according to the invention.  
         [0057]    In FIG. 1 a,  a pulse laser diode  1  a is a transmitter diode with pulse modulation that generates electromagnetic radiation with pulses P 1  as a signal. A suitable pulse duration is, for example, 50 nanoseconds. The strong signals generated thereby with optical powers in the Watt range are robust against foreign light reflections. Even sunlit reflective surfaces are therefore weaker than the signal pulse received.  
         [0058]    The radiation generated is emitted in a vertically oriented fan, which on the side of the device is generated by a combination of a lens  1   b  and a cylindrical lens array  1   c.  Alternatively, however, any other suitable components can be used, such as, for example, micro lens arrays or diffractive optical elements. After the emission and a reflection by a marker, which, for example, includes a retro reflector  2   a  as an example for a suitable reflector, reflective pulse P 2  is again received by the device.  
         [0059]    In this regard, on the receiver side, the fan-shaped view field is achieved by means of a slit aperture  4   a  before a receiver diode as a photosensitive element  4   b,  together with an objective  3  with cylindrical effect.  
         [0060]    In the second embodiment represented in FIG. 1 b,  on the side of the device in the transmitter unit  1 , the same components of pulse laser diode  1   a,  lens  1   b  and cylinder lens array  1   c  are used. However, now, as an example, two laser pulses with differing intensities are transmitted. Here, also, the pulse rate is in the kHz range. The radiation emitted now has a pulse P 11  with a higher maximum pulse height and a pulse P 12  with a lower maximum pulse height, which follow each other sequentially, and thus, in this embodiment, represent a double pulse.  
         [0061]    After reflection from the marker, which again has a reflector  2   a , the reflected pulses P 21  and P 22  are detected by the receiver unit. This again consists of an objective  3  with cylindrical effect and a slit aperture  4   a  before a receiver diode as a photosensitive element  4   b.    
         [0062]    Upon reception of the pulses of different intensity, the pulse that lies in the receiving dynamic range of the receiver is evaluated. In this example, for a shorter measuring distance whose limit, for example, may be 20 m, the reflected pulse P 22  with the lower pulse height is used, and for a greater measuring distance, the reflected pulse P 21  with the higher pulse height is used.  
         [0063]    [0063]FIG. 2 shows schematically a section of a two-dimensional intensity image with a marker object. The individual signal pulses  5  detected by the receiver are detected as a function of the time of their emission, with time triggered probing. At each laser pulse, a further signal track is created in the intensity image, along the distance axis. With time triggered probing, assignment is made with respect to distance and the emission times determine the horizontal angle associated with the signal track.  
         [0064]    Now, by analyzing the detected progress of the signal strengths, objects can be identified in the two-dimensional intensity image and their object width and distance measured. Markers and foreign markers or interference effects are differentiated through a plausibility test.  
         [0065]    [0065]FIG. 3 and FIG. 4 show schematically the performance of such a plausibility test for the recognition of markers. The basis of the plausibility test is the signal distance model and the object width distance model (tolerance value tables). The object width or object extension is calculated on the basis of the product of the number of pulses and angular speed. Additionally, it is possible to take into account or calculate the reflectivity of the marker.  
         [0066]    The object extension is an important recognition characteristic, since traffic signs always have greater reflective surface than the actual markers. An individual, specific tolerance value table can be kept for these object-specific characteristics for each marker type. At the same time, freely selectable tolerance value tables can be used for special user-specific markers. Also, alternative or supplementary plausibility tests based on other criteria can be performed. For example, where appropriate, spectrally different reflectivity of different objects can be analyzed.  
         [0067]    [0067]FIG. 3 shows an example of a plausibility test with respect to the signal amplitude using a plausibility band (tolerance value table). The plausibility test is performed by testing whether a measured value of a marker lies within a plausibility band which is defined in each case by a lower tolerance limit  8   a  and an upper tolerance limit  8   b.  The theoretical curve of all values of a marker is then represented by the distance-dependent profile  7   a.  For example, if a value for a foreign marker should lie on its profile, such as, for example, the profile  6   a  of a traffic sign, and therefore outside the plausibility band, it therefore would be identified as a foreign marker.  
         [0068]    Depending upon the concrete situation, such as, for example, the characteristic of the marker and of the possible foreign marker, it can be sufficient to work with only one tolerance limit, if this assures a safe division of the marker and foreign markers.  
         [0069]    Another procedure for plausibility checking with regard to the apparent object size, again using a plausibility band (tolerance value table), is represented in FIG. 4. What is represented is a tolerance value table that contains the apparent object width in time units, with a logarithmic scale in the case of a horizontal scan of the measuring device for the different distances, in which a marker-may be found. A measured apparent extension for a marker for which again the theoretical profile  7   b  is represented reflects the apparent extension in the horizontal direction. Here also, a test is made as to whether the measured value is within the plausibility band defined by the lower tolerance limit  8   c  and the upper tolerance limit  8   d.    
         [0070]    A value for a foreign marker width, for example, would lie near its theoretical profile  6   b  and therefore outside the plausibility band.  
         [0071]    [0071]FIGS. 5 a - b  show the conditions in the reflection of the pulse emitted at a retro reflector, as compared to the reflection from a foreign marker for the short range.  
         [0072]    [0072]FIG. 5 a  shows a schematic representation of the reflection from a retro reflector  2   a  at short range. The view fields of the transmitter unit  1  and the receiver unit that contains objective  3  and detector  4  are placed biaxially so that they do not overlap in the near range below 5 m and as a result are robust against foreign objects without retro reflection. The radiation from the transmitter unit  1  is reflected by the retro reflector  2   a  with a parallel offset and therefore can be received in the axis defined by the objective  3  and the detector  4  of the receiving unit.  
         [0073]    The situation that deviates from this in the case of reflection from a foreign marker  2   b  is shown in FIG. 5 b.  The foreigner marker does not lead to a parallel offset of the radiation emitted by the transmitter unit  1 , so that it cannot be received in the axis defined by the objective  3  and the detector  4 . A biaxial placement of the view fields of the transmitter unit  1  and the receiver unit therefore makes it possible to suppress the detection of foreign markers for the short range.  
         [0074]    In order to shorten the search time still further, multiple embodiment forms are possible on the receiver side. The fan-shaped view field can be subdivided into multiple sectors; alternatively multiple fans next to each other can be used. FIGS. 6 a - c  therefore show alternative embodiments of a receiver unit according to the invention, with structured fans, a horizontal fan tuft, and a two-dimensionally structured view field. In all examples, the sensor fan is divided into segments on the receiver side. As a result, a rough spatial position determination is possible in the fan direction as well.  
         [0075]    [0075]FIG. 6 a  shows the structuring of the fan of the receiver unit. The radiation emitted by the transmitter unit  1  and reflected from a retro reflector  2   a  is now received by means of a subdivision of the receiving fan, with additional location information. This subdivision of the fan  9   a  into multiple sectors can be achieved by means of a slit aperture  11   a  at the first focal point of the cylindrical receiver optics. In the embodiment represented in FIG. 6 a,  a switchable slit aperture can be used in which optionally the transmission from the relevant slit can be changed. The photosensitive element  12   a  is placed in the area of the second focal level in order to cover the view field of the receiver optics  10  in the spatial direction perpendicular to the fan with high transmission. The slit aperture  11  a divides the receiving fan into, for example, three sectors, which makes possible a rough positioning, even in the vertical direction. The radiation coming from the retro reflector  2   a  passes through the central opening of the slit aperture  11   a  in the example represented, so that a rough estimate of the angle range in the vertical direction can be made.  
         [0076]    A different embodiment of the receiver unit, according to the invention, with multiple fans, is shown in FIG. 6 b.  The generation of multiple receiving fans placed next to each other as a fan tuft  9   b  is done by using a structured photosensitive receiving surface  12   b  at the second focal level, especially in connection with a slit aperture  11   b  structured in the same arrangement. This subdivision of the photosensitive receiving surface  12   b,  for example in a linear array of photo detectors, thereby generates a tuft (cluster) of search fans placed next to each other. As an example, three fans are represented here; a different number of fans can be achieved through the choice of a suitable subdivision. Thus, especially tufts (clusters) with two or four fans can be achieved The central fan of this example, which is parallel to the transmission axis, reacts to the retro reflector  2   a , the fan turned toward the transmitter axis reacts to objects with single reflections, the third fan reacts only to sunlight reflections. A structured photosensitive receiving surface  12   b  therefore increases the certainty of correct identification of reflective objects.  
         [0077]    A receiver unit according to the invention with two-dimensional structuring of the view field is represented in FIG. 6 c.  Through the combination of two structured PIN diodes, whose structuring alignment in the right-hand angle is oriented toward each other, the view field can be subdivided two-dimensionally. The radiation detected by the receiving optics  10  with its view field is fed through a beam splitter  13  onto two different detectors. The first detector consists of a vertically structured photosensitive receiving surface  12   b  and a corresponding slit aperture  11   b  in the second focal plane. The second detector consists of a horizontally structured receiving surface  12   c  with associated slit aperture  11   c  in the first focal plane. As a result of this structuring oriented perpendicularly toward each other, the view field is divided horizontally and vertically, so that from this a tuft (cluster) of restructured fans results. In this example, with two PIN diodes lying side by side, retro reflection and the usual mirror reflection can be received with supplementary directional information and therefore can be differentiated.  
         [0078]    All suitable forms of location-sensitive detectors such as, for example, receiving diodes or receiving diode arrays or PSD&#39;s may be used as the described photosensitive elements  12   a  and receiving surfaces  12   b  and  12   c.    
         [0079]    The combination of a device  15  according to the invention, with an AZE system  16 , is represented together with the schematic progress of the process in FIGS. 7 a - b.    
         [0080]    [0080]FIG. 7 a  shows the structural integration of a device  15  according to the invention and an AZE system in a geodetic measuring device  14 . In this, the device  15  supplements the AZE system  16  already present in a theodolite as a geodetic measuring device  14 . The emission for the recognition of a retro reflector  2   a  as a marker by the device  15  according to the invention and the AZE system  16  takes place essentially parallel to each other in this example.  
         [0081]    [0081]FIG. 7 b  shows the combination of both search processes schematically. The device  15  in accordance with the invention carries out a rapid area scan with a vertical fan  17  to determine the horizontal angle of a marker. In a short time (a few seconds), a retro reflector  2   a  as a marker is found and its placement determined roughly. The measuring data of the device  15  according to the invention can be forwarded for support to other sensors in the geodetic measuring device, thus, for example, to an AZE system  16 . This AZE system  16  thereafter searches with its fan  18  also for the retro reflector  2   a  and therefore also determines the vertical angle. If the channels are separated from other optical sensors by means of suitable optical carrier wave lengths, then multiple sensors can be used simultaneously in the geodetic measuring device or multiple geodetic measuring devices can be used.  
         [0082]    [0082]FIG. 8 shows a block diagram for a device in accordance with the invention. A system clock A, which is connected to the image memory I, the electronic evaluation unit C, the control and signal processing unit B, the analog-digital converter H and the laser driver and controller E, serves as a common time base. The laser F emits radiation, which is sent to a retro reflector through beam-shaping optics  19 . After reflection, this beam is received and fed through an image-forming mask  20  to the detector G. The signal of this detector G is converted by the analog-digital converter H and processed further in the electronic evaluation unit C. This is connected to the control and processing unit B, the image memory I and the tolerance value tables J for all possible mark types. Through an interface, it is possible to connect to another system D, for example, a geodetic measuring device or the evaluation unit of a rotating device.  
         [0083]    In FIG. 9, a geodetic measuring system according to the invention, with automatic marker recognition using a bar code pattern on the marker, is shown. On a rod  21  of a marker, in addition to the marker, which here, as an example, is represented as a retro reflector  2   a , there is additionally a coded marker board  22 . The coding consists of optically strongly reflective strips that can be scanned sequentially in a search run. The vertical fan  17  illuminates a sufficiently large vertical angle, so that a parallel illumination and detection of the marker board  22  and the retro reflector  2   a  is possible. The signal received by the search sensor is amplitude modulated over time, so that the code of the marker board is transformed into a time sequence. As a result, it is possible to very rapidly search for the marker and identify the marker. Using a coordinate database, certain markers, as well as interfering objects, can be blanked out. Such points are not addressed. In the evaluation of the corresponding data image, the coded information from the marker board is also present, in addition to the object distance and object size.  
         [0084]    It is understood that the figures represent one of many embodiments and an expert can derive alternative embodiments, for example, using other means for emission and reception of electromagnetic radiation or for signal detection or signal processing.  
         [0085]    The foregoing discussion discloses and describes merely exemplary methods and embodiments of the present invention. As will be understood by those familiar with the art, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.