Abstract:
A stereomicroscopy system and method for generating at least a pair of representations of an object  7  for observation a user  9  are provided, comprising a detection system  15  for providing radiation data corresponding to detected radiation emanating from a region  17  of the object, a position detection apparatus  29  for detecting a position of the user, a location determination device  23  for determining a first and a second location in an object coordinate system  25 , an image data generation device  23  for generating image data from the radiation data for a first representation and a second representation representing the region of the object viewed from the first and second locations, respectively, and a display apparatus  75  for displaying the first representation for a left eye of the user and for displaying the second representation for a right eye of the user as a function of the image data.

Description:
FIELD OF THE INVENTION  
   The invention relates to a stereomicroscopy method and a stereomicroscopy system for producing at least a pair of representations of an object to be viewed by at least one user. 
   BACKGROUND OF THE INVENTION 
   The stereomicroscopy method according to the invention and the stereomicroscopy system according to the invention serve to produce stereoscopic representations of an object such that, when viewing the representations, the user obtains a three-dimensional impression of the representations. To this end, it is necessary for the left eye and the right eye of the user to perceive different representations of the object from different directions of view onto the object. 
   An example of a conventional stereomicroscopy system is a stereomicroscope. A beam path of a conventional stereomicroscope is schematically shown in  FIG. 1 . The stereomicroscope  901  shown there comprises an objective  903  with an optical axis  905  and an object plane  907  in which an object to be viewed is positioned. A beam bundle  911  emanating from the object and object plane  907 , respectively, in a solid angle region  909  around the optical axis  905  images the objective  903  to infinity and thus converts it into a parallel beam bundle  913 . Two zoom systems  915 ,  916 , each having an optical axis  917  and  918 , respectively, of its own are positioned adjacent each other in the parallel beam bundle  913  such that the optical axes  917  and  918  of the zoom systems are offset parallel to the optical axis  905  of the objective  903  and spaced apart from each other by a distance a. The two zoom systems  915 ,  916  each feed a partial beam bundle  919  and  920 , respectively, out of the parallel beam bundle  913 , with one partial beam bundle  919  being supplied to a left eye  921  of the user and the other partial beam bundle  920  being supplied to a right eye  922  of the user. To this end, a field lens  923 , a prism system  925  and an ocular  927  are disposed in the beam path of each partial beam bundle  919 ,  920 . As a result, the left eye  921  perceives the object  907  in a representation inclined at a viewing angle α in respect of the optical axis  5 , while the right eye  922  perceives the object  907  in a representation inclined at a viewing angle −α in respect of the optical axis  905 , as a result of which the user gets the stereoscopic, three-dimensional impression of the object. 
     FIG. 2  shows part of a beam path of a further conventional microscope  901  for providing a stereoscopic representation of an object for observation by two users. Similar to the microscope shown in  FIG. 1 , an objective  903  produces a parallel beam bundle from a beam bundle  911  emanating from the object in a solid angle region, with two zoom systems  915  and  916  being provided, each feeding a partial beam bundle  919  and  920 , respectively, out of the parallel beam bundle, said zoom systems supplying, via field lenses  923  and prism systems and oculars not shown in  FIG. 2 , representations of the object to the two eyes of a first user. 
   In the parallel beam path, there are further disposed two mirrors  931  which feed two further partial beam bundles  933  and  934  out of the parallel beam path and reflect the same such that they extend transversely to the beam direction of the partial beam bundles  919 ,  920 . The two partial beam bundles  933  and  934  are each supplied, via a zoom system  935  and  936 , respectively, and prism systems and oculars, likewise not shown in  FIG. 2 , to the two eyes of a second user. 
   In order for this microscope to be used by two users, it is required that, while observing the object, the two users are constantly in a fixed spatial position relative to the object and the microscope, respectively, and also relative to each other. In particular, if the microscope is used as surgical microscope during a surgical operation, this fixed spatial allocation is obstructive for the two users who must operate as surgeons in the operating field. 
   Accordingly, it is an object of the present invention to provide a stereomicroscopy method and a stereomicroscopy system which offers degrees of freedom for at least one user as regards his position relative to the object to be viewed. 
   SUMMARY OF THE INVENTION  
   To this end, the invention proceeds from the finding that in the conventional microscopes shown in  FIGS. 1 and 2  the radiation emanating from the object and processed by the objective, that is, the radiation emanating from the object towards the objective in the solid angle region and the parallel beam bundle passed on by the objective, respectively, comprise sufficient spatial information about the object to allow to produce therefrom stereoscopic representations of the object from a plurality of directions of view onto the object. Furthermore, it was found that merely the conventional way of using the information contained in the radiation emanating from the object, that is, the feeding of individual partial beam bundles out of the complete parallel beam bundle by the zoom systems and mirrors of the conventional microscopes shown in  FIGS. 1 and 2  has a limiting effect on the position of the users and the directions of view thereof onto the object. 
   Therefore, the invention proposes a stereomicroscopy method and a stereomicroscopy system, wherein a position of the user relative to a fixed point in a user coordinate system is detected. Dependent upon the position of the user in his user coordinate system, two locations relative to a region of the object to be observed are then determined in an object coordinate system. A first one of the two locations is allocated to the left eye of the user, while a second one of the two locations is allocated to the right eye of the user. Connecting lines between the thus determined locations and the region of the object to be observed define directions of view onto the object from which representations are produced by the method and the system which are supplied to the left eye and the right eye, respectively, of the user. These representations are produced by a stereoscopic display which receives corresponding image data. The image data supplied to the display are, in turn, produced from radiation data which are generated by a detector system which detects radiation emanating from the region of the object under observation. 
   The image data are produced from the radiation data dependent upon the two determined locations, that is, a virtual direction of view of the user onto the object. In this respect, it is, in particular, also possible to already carry out the detection of the radiation emanating from the object dependent upon these two locations so that the conversion of radiation data into the image data can be performed with more ease, or the radiation data can be used directly as image data. 
   All in all, when viewing the two representations of the stereo display device, the user obtains an impression of the object which is comparable to an impression which he would obtain if he viewed the object directly through a conventional stereomicroscope shown in  FIG. 1  or  2 . However, the user can change his position relative to the fixed point in the user coordinate system. As a result, representations of the object, which have been changed corresponding to his new position, are presented to him. When selecting his virtual direction of view onto the object, the user is thus not limited by the fixed optics of the conventional stereomicroscope. 
   Preferably, the generation of the image data from the radiation data comprises, first, the generation of a data model which is representative of the object and, further, the generation of the image data for the two representations from the data model. Here, the data model is at least partially a three-dimensional data model which reflects or represents the spatial structure and topography, respectively, of the surface of the object in at least a region thereof. 
   The generation of the at least partially three-dimensional data model comprises the use of a suitable topography detection apparatus which appropriately detects the radiation emanating from the object and calculates the data model on the basis of the thus obtained radiation data. To this end, use can be made of conventional topography detection apparatus and methods, such as line projection, pattern projection, photogrammetry and interferometric methods. 
   If the topography detection apparatus merely detects the three-dimensional structure of the surface of the object and does not detect surface properties of the object, such as color and texture, it is advantageous to also provide a detector device to detect, position-dependently, at least the color of the object surface in the region under examination and to provide corresponding color data. 
   The color information thus obtained is incorporated into the data model so that it is also represents colors of the object surface. 
   An advantageous photogrammetry method operates with two cameras which obtain images of the object at different viewing angles. 
   In this respect, it is again advantageous for a first one of the two cameras to record images of a larger region of the object with a lower spatial resolution and for a second camera to record merely images of a smaller partial region of the larger region with a higher spatial resolution. As a result, radiation data are obtained from the smaller partial region of the object which represent the three-dimensional topography of the object in said partial region. Accordingly, it is possible to generate a three-dimensional data model which represents the topography of the partial region of the object. From the region of the object which is observed merely by the first camera and which lies outside of the partial region observed also by the second camera there are thus radiation data obtained which are insufficient for generating a three-dimensional data model of this object region and merely represent the two-dimensional structure of the object in this region. However, these radiation data are also incorporated into the data model so that the latter also represents the entire object region observed by the first camera, said data model being then merely partially a three-dimensional data model. 
   If the partial region of the object which is also observed by the second camera is positioned centrally in the region of the object observed by the first camera, the user will perceive a three-dimensional, stereoscopic representation of the object with increased resolution in the center of his field of view. At the edge of his field of view he will perceive merely a two-dimensional representation of reduced resolution. The lack of a stereoscopic representation at the edge of the field of view is not always felt as disadvantageous by the user, while the increased resolution in the center of the field of view is perceived as advantageous. 
   The fixed point of the user coordinate system can be positioned within the region of the object under observation. When the object coordinate system and the user coordinate system are appropriately aligned relative to each other, the user, when viewing the stereoscopic display, will then perceive a representation of the object from the same perspective and direction of view as if he were viewing the object directly. 
   Alternatively, it is also possible to position the fixed point of the user coordinate system distant from the object so that the user and the object observed by the same can be spatially separated from one another. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention are described in further detail below with reference to drawings, wherein 
       FIG. 1  schematically shows a beam path of a conventional stereomicroscope, 
       FIG. 2  schematically shows part of a beam path of a conventional stereomicroscope, 
       FIG. 3  schematically shows an embodiment of a stereomicroscopy system according to the invention, 
       FIG. 4  shows a topography detection apparatus for use in the system shown in  FIG. 3 , 
       FIG. 5  illustrates a data model for the stereomicroscopy system shown in  FIG. 3 , 
       FIG. 6  shows a flow chart of the stereomicroscopy method described with reference to the stereomicroscopy system shown in  FIG. 3 , 
       FIG. 7  shows a variant of the topography detection apparatus shown in  FIG. 4 , 
       FIG. 8  shows a further variant of the topography detection apparatus shown in  FIG. 4 , 
       FIG. 9  shows a still further variant of the topography detection apparatus shown in  FIG. 4 , 
       FIG. 10  shows a still further variant of the topography detection apparatus shown in  FIG. 4 , and 
       FIG. 11  shows a variant of the position detection apparatus shown in  FIG. 3 . 
   

   DETAILED DESCRIPTION 
     FIG. 3  shows an operating room in which a stereomicroscopy system  1  according to the invention is installed. An operating table  5 , on which a patient  7  lies on whom a microsurgery is being performed by a surgeon  9 , is fixedly mounted on a floor  3  of the operating room. A stand  11  is fixedly mounted on the floor  3  of the operating room, said stand  11  pivotally holding a topography detection apparatus  15  on a pivotal arm  13  which is positioned above the patient  7  such that the topography detection apparatus  15  can record a surface geometry or topography of a region  17  of the patient  7 . The topography detection apparatus  15  operates optically. In  FIG. 3  optical beams which emanate from the region  17  of the patient  7  and are recorded by the topography detection apparatus  15  are schematically shown as dotted lines  19 . 
   The topography detection apparatus  15  obtains radiation data from this radiation  19  which are transmitted to a computer  23  via a data line  21 . On the basis of the thus obtained radiation data, the computer  23  reconstructs a three-dimensional structure or topography of the region  17  of the patient  7  as three-dimensional data model. This means that in a memory area of the computer there is a digital representation which is representative of the geometry or topography of the region  17  of the patient  7 . This data model is calculated in respect of a coordinate system x, y, z which is symbolically represented in  FIG. 3  below the reference sign  25 . 
   In order to correctly transform the three-dimensional data model into the coordinate system  25  of the operating room, the topography detection apparatus  15  carries a light-emitting diode  27 , the radiation of which is recorded by three cameras  29  which are mounted spaced apart from each other on the stand  11  and whose position in the coordinate system  25  of the operating room is known. The images of the cameras  29  are transmitted to the computer  23  via a data line  31 , said computer calculating a position of the topography detection apparatus  15  in the coordinate system  25  of the operating room on the basis of the images received. Accordingly, the radiation data obtained from the topography detection apparatus  15  are correctly incorporatable into the coordinate system  25  of the operating room. 
   It is also possible to provide three light-emitting diodes  27  spaced apart from each other so that an orientation of the topography detection apparatus  15  can be calculated as well in addition to the position thereof. In this case, the light-emitting diodes  27  can be provided to be distinguishable from each other by different light colors and/or blink frequencies. 
   The surgeon  9  carries a light-emitting diode  33  on his head, the position of which in the coordinate system  25  of the operating room being likewise detected by the cameras  29  and evaluated by the computer  23 . Accordingly, the computer  23  also detects the exact position of the surgeon  9  in the coordinate system  25 . Furthermore, the surgeon carries on his head a head-mounted display  35  which supplies a separate representation of the region  17  of the patient  7  to each eye of the surgeon  9 . The image data required for these representations for the two eyes of the surgeon are generated by the computer  23  from the three-dimensional data model of the region  17  of the patient  7 , and it supplies said image data to the display  35  via a data line  37 . 
   In so doing, the computer  23  generates the image data such that the surgeon  9 , when viewing the stereoscopic representation presented to him, gets an impression of the region  17  of the patient  7  as if he were directly viewing the region  17 , as it is symbolically represented in  FIG. 3  by a dotted sightline  39 . 
     FIG. 4  shows a part of the topography detection apparatus  15  in detail. The topography detection apparatus  15  works on a photogrammetry principle. To this end, it comprises two cameras  41  and  42  which are positioned spaced apart from each other such that each one of the cameras  41 ,  42  can record an image of a region  17  of a surface  43  of the patient  7 . Due to the distance between the two cameras  41 ,  42 , they take pictures of the region  17  at different viewing angles. As a result, the pictures taken by the cameras  41 ,  42  differ from each other. This is illustrated by the points  45 ,  46  shown exemplarily in  FIG. 4 . The two points  45 ,  46  are imaged in an image plane of the camera  41  as images  45 ′ and  46 ′, respectively, which are spaced apart from each other by a distance x 1  which is larger than a distance x 2  which image points  45 ″ and  46 ″ are spaced apart from each other in an image plane of the camera  42 . 
   By appropriately evaluating the images and radiation data, respectively, supplied by the cameras  41  and  42 , the computer  23  can then obtain a data model of the region  17  of the surface  43  of the patient  7 . 
   Further examples of photogrammetry methods and apparatus for this purpose are indicated, for example, in U.S. Pat. No. 6,165,181, the full disclosure of which is incorporated herein by reference. Further examples of photogrammetry methods are given in the references cited in said document. 
   The data model calculated for the region  17  is schematically shown in  FIG. 5  as a system of grid lines  49 . A data set of coordinates x, y and z of the intersections  51  is allocated to each intersection  51  of the grid lines  49 . The three-dimensional data model is thus represented by a plurality of number triplets which are representative of the coordinates of the surface  43  of the patient  7  in the region  17  in the coordinate system  25  of the operating room. Still further data sets can be allocated to each intersection  51  which are, for example, representative of color values or other properties of the object under observation at the respective locations. 
   This above-described representation of the data model in the memory of the computer  23  is, however, exemplary. There is a plurality of other memory techniques known for data models which are representative of three-dimensional structures in space. 
   At an intersection of the grid lines  49  disposed in a central region of the data structure, there is positioned a fixed point  53  which serves, on the one hand, as point of origin of a user coordinate system  55  and, on the other hand, as center of a central region of the object  7  which is presented to the surgeon  9  such that the latter gets the impression that his view  39  is directed to said fixed point  53  of the central region. The position of the surgeon  9  in the user coordinate system  55  is expressed by azimuths φ about a vertical axis z′ oriented parallel to the z axis of the object coordinate system  25 , and that proceeding from an arbitrary straight φ 0  extending horizontally in the object coordinate system  25 . 
   Two locations P 1  and P 2  are determined in the object coordinate system  25 , for example, as coordinates x, y, z which, in the user coordinate system  55 , have different azimuths φ and φ′ and the same elevation θ. The elevation θ can be the elevation at which the sightline  39  of the surgeon strikes the region  17  of the object  7 . An average value between the two azimuths φ and φ′ corresponds approximately to the azimuth at which the surgeon  9  is oriented relative to the patient  7 . The difference between φ and φ′ can have a predetermined value, such as about 20°, for example. However, it may also be selected as a function of a distance of the surgeon  9  from the fixed point  53  and decrease with increasing distance. 
   The computer  23  generates the image data for the representation of the region  17  of the patient  7  by the head-mounted display  35  such that a representation is presented to the left eye of the surgeon  9  as it would appear upon observation of the three-dimensional data model from location P 1 , whereas the image data for the representation which is presented to the right eye are generated such that the three-dimensional data model appears as viewed from location P 2 . 
   If the position of the surgeon  9  in the user coordinate system  55  changes azimuthally by an angle Φ 2  and elevationally by an angle θ 2 , the locations P 1  and P 2  are shifted in the object coordinate system  25  to locations P 1 ′ and P 2 ′ such that the new positions thereof have changed azimuthally by the angle Φ 2  and elevationally likewise by the angle θ 2  in respect of the fixed point  53  as compared to the previous positions. 
   In the following, the stereomicroscopy method is again described with reference to the flow chart of  FIG. 6 . 
   The object  17  is recorded by the two cameras  41  and  42  from different perspectives. The cameras  41 ,  42  supply radiation data  59 ,  60 , which correspond to the pictures taken by the same, to the computer  60 , said computer generating a three-dimensional data model  63  of the object  17  under observation from the radiation data  59  and  60  by means of a topography reconstruction software module  61 . 
   The stereomicroscopy system can present representations of the object under observation to left eyes  65 L and right eyes  65 R of several users. To this end, a position detection apparatus  67  is allocated to each user for detecting the position, for example, of a point at the user&#39;s head between the two eyes  65 L,  65 R in the user coordinate system  55  and for generating corresponding position data  69 . These position data are supplied to a representation generator or rendering engine  71  which generates image data from the 3D model  63  which are supplied to displays  75  viewed by the user&#39;s eyes  65 . 
   The rendering engine  71  generates for each user image data  73 L and  73 R which generate representations for the left eye  65 L and the right eye  65 R of said user on displays  75 L and  75 R, respectively. Accordingly, representations of the object  7  are thus presented to each user via the displays  75 L and  75 R which are perceived by the user as if he viewed the object  17  from a perspective which corresponds to the perspective as if the user viewed the object  17  directly from his standpoint. 
   In the above-described embodiment, the fixed point  53  of the user coordinate system in which the position of the user is detected is disposed centrally in the region  17  of the object  7  under observation. This is appropriate if the user is to perform manipulations directly on the object  7  under observation, as it applies to the case of the surgeon in the operating room shown in  FIG. 3 . 
   However, it is also possible for the user to be positioned remote from the object under observation and thus the fixed point of the user coordinate system does not coincide with the region of the object under observation. An example for such an application would be a telesurgical method wherein the surgeon is positioned distant from the patient and performs the operation on the patient by means of a remote-controlled robot. In this case, the fixed point for determining the position data  69  is then positioned in the field of view of the surgeon or user, and an image is defined between the user coordinate system and the coordinate system of the operating room by means of which the fixed point in front of the surgeon can be transferred, for example, into the region of the patient under observation. By moving his head, the surgeon positioned remote from the patient is then also able to obtain impressions from the patient under operation from different perspectives. 
   It is also possible to position the observer remote from the object under observation if, for example, there is only space for a few people at the operating table and further persons, for example, students wish to observe the operation directly “flesh-and-blood”. These person can then be positioned outside of the operating room. A fixed point and its orientation in the user coordinate system can be determined in space for each one of these persons so that, when viewing their head-mounted display, they get the impression as if the region of the patient under observation were disposed around this very, namely, their personal fixed point. 
   In the following, variants of the embodiment of the invention illustrated with reference to  FIGS. 1 to 6  are described. Components which correspond to each other in structure and function are designated by the same reference numbers as in  FIGS. 1 to 6 . For the purpose of distinction, they are, however, supplemented by an additional letter. For the purpose of illustration, reference is taken to the entire above description. 
     FIG. 7  schematically shows a topography detection apparatus  15   a  which is similar to the topography detection apparatus shown in  FIG. 4  in that it likewise works on the photogrammetry principle. A camera  41   a  records an image of a larger region  17   a  of the object under observation. A further camera  42   a  records an image of a smaller partial region  79  disposed centrally in the region  17   a  recorded by the camera  41   a . Both cameras  41   a  and  42   a  have the same resolution capability, i.e., the numbers of their light-sensitive pixels is the same. Accordingly, the camera  41   a  achieves with the pictures taken and the image data generated by the camera  41   a , respectively, a lower resolution at the object under observation than the camera  42   a . In the partial region  79 , the object is recorded from two different perspectives by the cameras  41   a  and  42   a  so that a three-dimensional data model can be reconstructed in this partial region  79  which is representative of the spatial structure of the object in this partial region  79 . However, it is not possible to reconstruct the structure of the object three-dimensionally for the part of the region  17   a  which lies outside of the partial region  79 . However, the (two-dimensional) radiation data of the camera  41   a  are used for the part of the region  17   a  which lies outside of the partial region  79  for providing a corresponding two-dimensional representation of the object in this region. 
     FIG. 8  shows a variant of the topography detection apparatus shown in  FIGS. 4 and 7 . A topography detection apparatus  15   b  shown in  FIG. 8  likewise forms part of a stereomicroscopy system  1   b  and comprises a microscope objective  81  with an optical axis  83 . An object  7   b  is positioned in an object plane of the objective  81 . The objective  81  images the object  7   b  to infinity. Furthermore, a lens system  85  is disposed along the optical axis  83  spaced apart from the objective  81  such that an image of the region  17   b  of the object  7   b  under observation is formed on a CCD chip  87  positioned in an image plane of the lens system  85 . 
   In a parallel beam path between the objective  81  and the lens system  85 , there is disposed a switchable stop  89 , the switching state of which is controlled by a computer  23   b.    
   The radiation data recorded by the CCD chip  87  are supplied to the computer  23   b.    
   The switchable stop  89  has a plurality of separately controllable liquid crystal elements. Outside of two circular, spaced apart regions  91  and  92 , the liquid crystal elements are always in a switching state in which they do not allow light to pass through. The circular regions  91  and  92  are alternately switched to a substantially light-permeable state and a substantially light-impermeable state. 
   In the switching state shown in  FIG. 8 , the region  91  is switched to its light-permeable state, while the region  92  is switched to its light-impermeable state. Accordingly, a partial beam bundle  93  of the complete beam bundle emanating from the objective  81  passes through the switchable stop  89  and is imaged on the CCD chip  87  by the lens system  85 . Accordingly, only light of a conical beam bundle  95  emanating from the region  17   b  under observation at an angle α in respect of the optical axis  83  impinges on the chip  87 . The chip  87  thus records an image of the region  17   b  under observation as it appears when viewed at an angle α in respect of the optical axis  83 . Radiation data which are representative of this image are transmitted to the computer  23   b.    
   The computer  23   b  then controls the stop  89  to switch the liquid crystal elements to their light-impermeable state in the region  91 , while the liquid crystal elements are switched to their light-permeable state in the region  92 . Accordingly, a partial beam bundle  94  passes through the stop  89  which corresponds to a conical beam bundle  96  emanating from the object  7   b  at an angle −α in respect of the optical axis  83  and which is also imaged on the detector  87  by the lens system  85 . The detector  87  thus records an image of the object  7   b  at an angle −α in respect of the optical axis in this switching state. This image, too, is transmitted as radiation data to the computer  23   b.    
   Accordingly, the computer  23   b  receives, successively in time, radiation data of the object at respectively different directions of view onto the object. On the basis of these radiation data, the computer  23   b  can in turn generate a three-dimensional data model of the object  7   b , as it has already been described above. 
     FIG. 9  shows a further variant of the topography detection apparatus shown in  FIG. 8 . In contrast to the topography detection apparatus shown in  FIG. 8 , the apparatus  15   c  shown in  FIG. 9  records images from different perspectives of an object  7   c  not successively in time, but simultaneously. To this end, a color CCD chip  87   c  is disposed on an optical axis  83   c  on which a lens system  85   c  and an objective  81   c  and a region  17   c  of the object  7   c  under observation are disposed such that the region  17   c  under observation is imaged on the color CCD chip  87   c , and a parallel beam path is formed between the lens system  85   c  and the objective  81   c . Between the objective  81   c  and the lens system  85   c , there is disposed a stop  89   c  which is light-impermeable, except for circular regions  91   r ,  91   g ,  91   b . The light-permeable regions  91   r ,  91   g ,  91   b  are disposed spaced apart from each other and from the optical axis  83   c  and circumferentially distributed about the same. The circular region  91   r  allows only red light to pass through, the region  91   g  allows only green light to pass through, and the region  91   b  allows only blue light to pass through. The color CCD chip  87   c  supplies radiation data for each of the colors red, green and blue to the computer  23   c . The images of the object  17   c  recorded in the different spectral colors have thus each been recorded from different perspectives and angles in respect of the optical axis  83   c . By appropriately evaluating these radiation data, the computer  23   c  can, in turn, generate a three-dimensional data model of the object  7   c.    
     FIG. 10  schematically shows a further variant of a topography detection apparatus  15   d  which works on a pattern projection principle. The structure of the topography detection apparatus is similar to that of the conventional microscope shown in  FIG. 1  and comprises an objective  81 d which is disposed along an optical axis  83   d , an object to be observed being disposable in the object plane  95  thereof. Two zoom systems  97  and  98  are provided spaced apart from the optical axis  83   d  which are allocated to a left eye and a right eye of a user, respectively, so that the user can observe the object also directly through the microscope in conventional manner. In addition to the conventional observation of the object, there is provided an infrared light source  99  which illuminates a stop  101  which is imaged in the object plane  95 . To this end, a condenser  103  is provided as well as a dichroidic mirror  105  to feed the image of the stop  101  into the beam path of the microscope such that the light of the infrared light source  99  passing through the stop  101  passes also through the objective  81   d  of the microscope. The stop  101  has a grid structure which is imaged by the infrared light in the object plane  95 . Accordingly, a pattern projected with infrared light is formed in the object plane  95 , with infrared light being reflected by those regions of the object surface which are illuminated with infrared light. Here, the projection of the pattern onto the object is effected at an angle −α in respect of the optical axis  83   d . The infrared light reflected by the object which returns to the objective  81   d  at an angle α in respect of the optical axis  83   d  is fed out of the beam path of the microscope by means of a dichroidic mirror  107  and imaged on an infrared camera  109 . 
   By evaluating the image obtained by the camera  109  it is thus possible to reconstruct the three-dimensional structure of the object under observation and to record it as three-dimensional data model. This three-dimensional data model, in turn, can be used for generating representations for a user who views these representations via a stereo display system. 
   Further examples of pattern projection methods are indicated, for example, in U.S. Pat. No. 4,498,778, in U.S. Pat. No. 4,628,469 and in U.S. Pat. No. 5,999,840, the full disclosure of each document being incorporated herein by reference. 
   Although the reconstruction of the topography of the object on the basis of the projected pattern allows to reconstruct the three-dimensional structure of the object, it is not possible to obtain also information on the surface color solely by the pattern projection. Therefore, a semi-transparent mirror  111  is positioned in the beam path of the microscope to feed light out for a camera  113  which is sensitive in the visible range. The radiation data of said camera are used to incorporate color information into the three-dimensional data model of the object generated on the basis of the radiation data obtained from the camera. 
     FIG. 11  schematically shows a variant of a position detection apparatus  29   e . For example, it could be mounted directly on or at the topography detection apparatus shown in  FIG. 3  for detecting a position of the user in the operating room relative to the topography detection apparatus. 
   To this end, an optical axis  123  of the position detection apparatus  29   e  would have to be oriented vertically in the operating room. The position detection apparatus  29   e  comprises a conical mirror  125  which reflects radiation impinging on the mirror  125  at an angle of ±γ in respect of a horizontal plane  127  onto an optical system  131  which images the radiation on a CCD chip  121 . 
   This system  29   e  allows to locate a user carrying a light source at his head in the operating room, because his azimuthal position about the axis  123  as well as his elevation in respect of the plane  127  in a range ±γ is determinable by evaluation of the image of the CCD chip  121 . If there are several users in the operating room, it is possible for each user to carry a light source, the light intensity of which changes time-dependently, a separate characteristic time pattern for the light intensity being provided for each user. By evaluating the image of the camera  121  and taking into consideration the recorded time pattern, it is thus possible to detect the position of each one of the users. 
   With the topography detection apparatus shown in  FIG. 8  it is possible to supply a stereoscopic image of the object, position-dependently, to a user without a complete three-dimensional data model of the object having to be reconstructed. The camera  87  shown in said Figure records images successively in time and corresponding radiation data are supplied which correspond to different directions of view −α and α, respectively, onto the object  7   b . These radiation data can now be used directly as image data for producing representations for the user&#39;s left eye and the right eye, respectively. For example, the radiation data which are obtained when the region  91  is light-permeable and the region  92  is light-impermeable can be used as image data for the right eye, and the radiation data which are obtained when the region  92  is light-permeable and the region  91  is light-impermeable can be used as image data for the left eye. As a result, a full stereoscopic impression of the object  7   b  is produced for the observer when he views these representations. 
   If the user changes his position azimuthally about the optical axis  83  of the objective, it is then also possible to likewise shift the alternately light-permeable and light-impermeable regions  91  and  92  azimuthally about the optical axis, which is enabled by correspondingly controlling the liquid crystal elements of the switchable stop  89 . This displacement of the regions  91  and  92  is indicated in  FIG. 8  by arrows  141 .