fig1 illustrates an exemplary rigid body that includes marker elements , wherein the rigid body is identified by means of a navigation and / or tracking system . more specifically , the marker elements a , b , and c may be arranged on a reference array 1 via arms 2 and attached to an instrument 3 , wherein the rigid body may be identified by moving the instrument 3 within the working range of the navigation system 10 and / or tracking system 7 . while an optical tracking is shown , other tracking systems may be utilized , including , for example , ultrasound , magnetic or laser tracking and navigation systems . the instrument 3 comprises a tip 6 , and a spatial arrangement of the marker elements a , b , and c on the reference array 1 is fixed , such that the distances ab , ac and bc of the three marker elements form a rigid body and / or rigid marker body geometry . the distances ab , ac and bc can be detected by the tracking system 7 , which can operate stereoscopically , i . e ., using two cameras having lines of sight 8 and 9 . due to the stereoscopic scanning of the tracking system 7 , it is possible to determine the absolute positions of the marker elements a , b and c as well as their respective distances . the tracking system 7 can be connected to the navigation system 10 , which comprises a screen output 11 ( the navigation system 10 and screen output 11 are only shown schematically ). the navigation system 10 can receive and process the positional data ascertained by the tracking system 7 , and display the data via the screen output 11 ( also referred to as display 11 ) so as to provide image assistance . the navigation system 10 also may perform assignment and identification measures . the embodiment shown indicates one way in which the position of the tip 6 of the instrument 3 can be detected . to this end , a positioning recess 12 can be provided for the tip of the instrument 3 , wherein the recess may be arranged at a spatially fixed point . a location of the recess in three dimensional space , however , need not be known . in the present example , the recess 12 has a funnel - shaped cavity that allows the tip 6 to be fixed but still allows the instrument to move . in the present case , the movement is performed as a pivoting movement about the fixed tip 6 , as indicated by the arrow 5 . by measuring the distances between the marker elements a , b and c , this specific marker configuration having said specific relative distances of the marker elements can be identified as an assignable spatial arrangement of marker elements . the rigid body predetermined by the marker geometry can be determined , for example , by performing a pivoting movement about the fixed tip 6 , or beforehand during another movement of the instrument within the visual field of the tracking system 7 . since the marker elements a , b , and c move about the tip 6 in circular movements and / or movements on the surface of a sphere , the center of this movement also can be ascertained , said center being the position of the tip 6 . the position of the spatial arrangement of marker elements can be assigned to the position of the tip 6 , and the position of the tip 6 then is always known in the navigation system 10 . after this process , the instrument 3 can continue to be navigated as a tracked instrument and used in image - assisted surgery , even though it has not been previously stored and / or identified in a data set of the navigation system 10 . a patient landmark or a marking point of a treatment - assisting instrument also could be selected instead of the positioning recess 12 , such that said point could be simultaneously registered . using the above method , any instrument , even cost - effectively produced instruments that comprise rigid body marker arrangements , can be used for navigation and / or tracking . it is also possible to improve the accuracy of pre - calibrated tools , if the tolerances of theses tools due to production problems or attrition become critical . fig2 illustrates the exemplary computer system 20 that may be used to implement the method described herein ( e . g ., as a computer of the navigation system 10 and / or tracking system 7 ). the computer system 20 may include a display 22 for viewing system information ( which may be in addition to the display 11 , or may be the display 11 ), and a keyboard 24 and pointing device 26 for data entry , screen navigation , etc . a computer mouse or other device that points to or otherwise identifies a location , action , etc ., e . g ., by a point and click method or some other method , are examples of a pointing device 26 . alternatively , a touch screen ( not shown ) may be used in place of the keyboard 24 and pointing device 26 . the display 22 , keyboard 24 and mouse 26 communicate with a processor via an input / output device 28 , such as a video card and / or serial port ( e . g ., a usb port or the like ). a processor 30 , such as an amd athlon 64 ® processor or an intel pentium iv ® processor , combined with a memory 32 execute programs to perform various functions , such as data entry , numerical calculations , screen display , system setup , etc . the memory 32 may comprise several devices , including volatile and non - volatile memory components . accordingly , the memory 32 may include , for example , random access memory ( ram ), read - only memory ( rom ), hard disks , floppy disks , optical disks ( e . g ., cds and dvds ), tapes , flash devices and / or other memory components , plus associated drives , players and / or readers for the memory devices . the processor 30 and the memory 32 are coupled together via a local interface ( not shown ). the local interface may be , for example , a data bus with accompanying control bus , a network , or other subsystem . the memory may form part of a storage medium for storing information , such as application data , screen information , programs , etc ., part of which may be in the form of a database . the storage medium may be a hard drive , for example , or any other storage means that can retain data , including other magnetic and / or optical storage devices . a network interface card ( nic ) 34 allows the computer system 20 to communicate with other devices . a person having ordinary skill in the art of computer programming and applications of programming for computer systems would be able in view of the description provided herein to program a computer system 20 to operate and to carry out the functions described herein . accordingly , details as to the specific programming code have been omitted for the sake of brevity . also , while software in the memory 32 or in some other memory of the computer and / or server may be used to allow the system to carry out the functions and features described herein in accordance with the preferred embodiment of the invention , such functions and features also could be carried out via dedicated hardware , firmware , software , or combinations thereof , without departing from the scope of the invention . computer program elements of the invention may be embodied in hardware and / or in software ( including firmware , resident software , micro - code , etc .). the invention may take the form of a computer program product , which can be embodied by a computer - usable or computer - readable storage medium having computer - usable or computer - readable program instructions , “ code ” or a “ computer program ” embodied in the medium for use by or in connection with the instruction execution system . in the context of this document , a computer - usable or computer - readable medium may be any medium that can contain , store , communicate , propagate , or transport the program for use by or in connection with the instruction execution system , apparatus , or device . the computer - usable or computer - readable medium may be , for example but not limited to , an electronic , magnetic , optical , electromagnetic , infrared , or semiconductor system , apparatus , device , or propagation medium such as the internet . note that the computer - usable or computer - readable medium could even be paper or another suitable medium upon which the program is printed , as the program can be electronically captured , via , for instance , optical scanning of the paper or other medium , then compiled , interpreted , or otherwise processed in a suitable manner . the computer program product and any software and hardware described herein form the various means for carrying out the functions of the invention in the example embodiments . although the invention has been shown and described with respect to a certain preferred embodiment or embodiments , it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings . in particular regard to the various functions performed by the above described elements ( components , assemblies , devices , compositions , etc . ), the terms ( including a reference to a “ means ”) used to describe such elements are intended to correspond , unless otherwise indicated , to any element which performs the specified function of the described element ( i . e ., that is functionally equivalent ), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention . in addition , while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments , such feature may be combined with one or more other features of the other embodiments , as may be desired and advantageous for any given or particular application .