Patent Publication Number: US-2011053120-A1

Title: Marksmanship training device

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation-in-part of U.S. patent application Ser. No. 11/414,559, filed May 1, 2006, entitled “Marksmanship Training Device.” 
    
    
     FIELD OF THE INVENTION 
     The current invention relates to a simulator for training small arms marksmanship skills which involve firing over long distances and where the required angular movement of the barrel is slow. 
     BACKGROUND OF THE INVENTION 
     There are numerous weapon simulator devices that have been utilized for training marksmen and other personnel for combat situations, as well as for law-enforcement. The technology enabling the construction of such devices started becoming viable with the introduction of solid-state electronics in the 1970&#39;s. Over the last two decades the scientific community has conducted controlled experiments in order to evaluate the effectiveness of these devices for training and assessing marksmen. None of the experiments have found evidence of any significant benefit for marksmanship training, in particular the ability to locate a group of shots in tight proximity onto a target. Furthermore, none of the studies have found high correlations between marksmanship performance in the simulator and that in the live environment (i.e., a marksman&#39;s live-fire performance is not well-predicted by their performance in the simulator). Such outcomes imply that these devices have limited utility for training and assessing marksmanship skills. While the scientific literature has highlighted these shortcomings, the scientific community has tended to caution against over reliance on the use of these simulators and have not identified any solutions to these problems in terms of improvements to the simulator. 
     The task of marksmanship requires the use of very fine perceptual-motor skills. In general, marksmanship tasks can be divided into two types. The first type involves firing over long distances at targets subtending small angles at the weapon (e.g., a marksman firing at a static target on a rifle range at 100 metres, or a sniper attempting to fire at a partially concealed man-size target at several hundred metres). This type of task is best conducted from the prone position mainly because this enables the shooter to steady the barrel, and because engagement of the static or slow-moving target does not require rapid angular movement of the barrel of the weapon. The second type of marksmanship task involves firing at close-range, fast-moving targets, such as occurs in combat pistol tasks and in the recreational field of clay-pigeon or skeet shooting. This latter task is typically conducted from a standing position to give the marksman greater freedom of movement and allow rapid angular movement of the barrel of the weapon. However, these factors lead to less stability of the barrel, which in turn leads to less accuracy in aiming the weapon and hence this type of task is more often conducted over closer ranges. 
     Computer generated target imagery found in current small arms simulators is limited by the resolution of that imagery which is significantly lower than the eye-limited resolution of targets on a live firing range and thus the degraded target results in significant shortcomings in marksmanship performance. When training marksman to aim, acquire and engage a target, it is important that the limiting factor is the visual acuity of the marksman and not visual artifacts in the simulated target image. 
     Marksmanship performance is often measured in terms of a hit or miss of the target. It is acknowledged that hitting a target is an important measure of performance in marksmanship training. However, when undertaking marksmanship training, other important measures include the extreme spread which is the distance between the two most widely separated shots in a group of shots and shows the ability of the marksman to maintain a consistent point of aim. When specifying the accuracy requirements for the weapon aim-point calculation in a marksmanship simulator, it should be apparent that any measurement error should be insignificant compared to the requirements of the marksmanship task being trained or assessed. In current small arms simulators, the weapon aim-point and fall of shot position locations are not calculated by the hit detection systems to a level of precision sufficient to support the reliable assessment and training of marksmanship skills, in particular for shooting at targets over long ranges. 
     The invention described herein provides a method and apparatus arrangement to overcome, or at least substantially reduce the disadvantages and shortcomings in prior art by ensuring that the marksman&#39;s performance is not confounded by (a) the quality of the target image and/or (b) the accuracy of the weapon aim-point determination. 
     Thus a simulator arrangement and method of use is described for training marksmanship tasks which involve firing over long distances and where the required angular movement of the barrel is slow. 
     Additionally further advantages of the present invention will become apparent from the following description, in connection with the accompanying drawings, where, by way of illustration and example, embodiments of the present invention are disclosed. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In a broad aspect of the invention a marksmanship simulator for the training of a marksman includes: a target area projector projecting a density of pixels on the screen than such that an individual pixel is not visible to the vision assisted or vision non-assisted marksman, wherein the pixels form a target image within the target area; a screen for receiving and reflecting projected visible and non-visible radiation; a background projector for projecting an image on the screen and over a target area, wherein the contrast ratio of the target image formed by both the background projector and target area projector is substantially that of the target area projector. 
     In a further aspect of the invention a marksmanship simulator further includes a marksmanship training weapon for projecting a non-visible laser footprint onto the screen; and a detector for detecting the reflected non-visible laser footprint on the screen wherein the density of the detector pixels for receiving the non-visible footprint and the intensity and size of the laser footprint is such that there is a predetermined accuracy of the detection of the location of footprint. 
     In yet a further aspect of the invention a marksmanship simulator further includes a processor for receiving the detector signal representing the location of the non-visible laser footprint and also knowing the location of the projected pixels of the background image and target area and determining the location of the non-visible laser footprint with respect to one or more of the pixels of either or both the background image or the target area. 
     In yet a further aspect of the invention a marksmanship simulator further includes a detector arranged to detect the non-visible laser only if it lies near or within the target area. 
     In yet a further aspect of the invention a marksmanship simulator further includes a background projector which maximizes the contrast ratio in the target area by minimizing the brightness in the target area projected by the background projector. 
     In yet a further aspect of the invention a marksmanship simulator further includes a mechanism for moving both the target area projector and the detector such that the detector is detecting the non-visible footprint in or about the target area. 
     In yet a further aspect of the invention a marksmanship simulator further includes a marksmanship arrangement having a screen for receiving and reflecting projected visible and non-visible radiation, a projector for projecting a density of visible pixels on the screen substantially within a target area and a marksmanship training weapon for projecting a non-visible laser footprint onto the screen, including a detector for detecting the reflected non-visible laser footprint on the screen wherein the density of the detector pixels for receiving the non-visible footprint and the intensity and size of the laser footprint is such that there is a predetermined accuracy of the detection of the location of footprint. 
     In yet a further aspect of the invention a marksmanship simulator further includes a marksmanship training weapon for projecting a non-visible radiation footprint including a target area image capable or reflecting non-visible radiation, and a detector for detecting the reflected non-visible radiation footprint from the target wherein the density of the detector pixels for receiving the non-visible footprint and the intensity and size of the laser footprint is such that there is a predetermined accuracy of the detection of the location of footprint. 
     In yet a further aspect of the invention a marksmanship simulator further includes a marksmanship simulator wherein the target area image is illuminated. 
     In yet a further aspect of the invention a marksmanship simulator further includes a marksmanship simulator wherein the target area image is illuminated by non-visible light. 
     It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, or a computer readable medium such as a computer readable storage medium or a computer network wherein program instructions are sent over wireless, optical or electronic communication links. It should be noted that the order of the steps of disclosed processes may be altered within the scope of the invention. 
     Details concerning computers, computer networking, software programming, telecommunications and the like may at times not be specifically illustrated as such were not considered necessary to obtain a complete understanding nor to limit a person skilled in the art in performing the invention, are considered present nevertheless as such are considered to be within the skills of persons of ordinary skill in the art. 
     A detailed description of one or more preferred embodiments of the invention is provided below along with accompanying figures that illustrate by way of example the principles of the invention. While the invention is described in connection with such embodiments, it should be understood that the invention is not limited to any embodiment. On the contrary, the scope of the invention is limited only by the appended claims and the invention encompasses numerous alternatives, modifications, and equivalents. For the purpose of example, numerous specific details are set forth in the following description in order to provide a thorough understanding of the present invention. The present invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the present invention is not unnecessarily obscured. 
     Throughout this specification and the claims that follow unless the context requires otherwise, the words ‘comprise’ and ‘include’ and variations such as ‘comprising’ and ‘including’ will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. 
     The reference to any background or prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such background or prior art forms part of the common general knowledge. 
     Specific embodiments of the invention will now be described in some further detail with reference to and as illustrated in the accompanying figures. These embodiments are illustrative, and not meant to be restrictive of the scope of the invention. Suggestions and descriptions of other embodiments may be included within the scope of the invention but they may not be illustrated in the accompanying figures or alternatively features of the invention may be shown in the figures but not described in the specification. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  depicts a marksmanship simulator arrangement of an embodiment of the invention; 
         FIG. 2  depicts alternative arrangements according to embodiments of the invention for projecting the target image onto a screen; 
         FIG. 3  depicts prior art projection of the background and target image using a background projector; 
         FIG. 4   a  depicts prior art target area resolution and target image as displayed by the background projector and as seen by a marksman; 
         FIG. 4   b  depicts target area resolution and target image as displayed by the target projector wherein the target image is at better than eye-limited resolution as seen by the marksman according to an embodiment of the invention; 
         FIG. 5  illustrates the geometry associated with the calculation of the maximum projected pixel size to achieve an eye limited resolution of the target area; 
         FIGS. 6   a  and  6   b  show light intensity plots on the simulator screen for purposes of illustrating the effect of two projectors on the contrast ratio of the background and target area images; 
         FIG. 7  depicts prior art detection of the laser footprint. 
         FIGS. 8   a ,  8   b  and  8   c  depict the characteristics of the laser footprint where the size of the laser footprint is larger than that of each detector pixel, and the pixel intensity before and after application of a suitable threshold; 
         FIGS. 9   a ,  9   b  and  9   c  depict the characteristics of the laser footprint where the size of the laser footprint is smaller than that of each detector pixel, and the pixel intensity before and after application of a suitable threshold; 
         FIG. 10  depicts detection of the laser footprint for an embodiment of the invention. 
         FIGS. 11   a  and  b  depict the characteristics of the laser footprint for one embodiment of the invention where the size of the laser footprint is larger than that of each detector pixel, and the pixel intensity before and after application of a suitable threshold; 
         FIGS. 12   a  and  b  depict the characteristics of the laser footprint for one embodiment of the invention where the size of the laser footprint is smaller than that of each detector pixel, and the pixel intensity before and after application of a suitable threshold; 
         FIG. 13  depicts a flow diagram of the hit detection process; 
         FIG. 14  illustrates the pixel intensity before the application of a suitable threshold as described in  FIG. 13 ; 
         FIG. 15  illustrates the pixel intensity after the application of a suitable threshold as described in  FIG. 13 ; 
         FIG. 16  depicts a geometric representation of steps  8 - 13  in the hit detection process for  FIG. 13 ; 
         FIG. 17  depicts the output provided by the processor as feedback to marksman and instructors. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     As mentioned previously, the target image is preferably presented to the marksman at better than eye-limited resolution. In the context of a marksmanship simulator, the term “eye-limited resolution” is taken to mean a simulated target image of such quality that when a marksman, with normal (that is 20/20 vision), looks through the simulator aiming device sees a target that does not have any additional visible artifacts that are not present in the equivalent real-world target. In particular, with regards to this invention, such an image is provided under those conditions when the marksman can not detect individual picture elements (in a digital display the term pixel is used to describe such an element). The image seen by the marksman is thus absent of any indication that it has been generated electronically even though it will be understood by the marksman that the image has been projected from an electronic image generating device. 
     Referring to  FIG. 1  an embodiment of one aspect of the invention is depicted, including a marksmanship training weapon  1  for projecting a non-visible laser footprint onto the screen  6 . The weapon is shown with an eye-sight aim assistance device, typically referred to as a sight  2 , for viewing the target image  19 . The target area  8  contains an image  19  which can be viewed through the sight  2  of the weapon  1  to give a field of view  10 . The weapon  1  includes a laser that emits radiation in the form of a non-visible laser beam (although other forms of radiation may be useable) from the barrel  3  of the weapon which strikes the screen  6  which receives and reflects the projected non-visible laser footprint, the footprint  7  being preferably, according to the skill of the marksman, within the target area  8 . 
     A target area  8  can be projected anywhere on the screen  6  by the target area projector  16 , this may be a bulls-eye or other type of target used for marksmanship training (animate or inanimate object) along with a suitable background image  9  (none specifically shown). 
     A background projector  4  projects an image  9  on the screen  6  and invariably also over the target area  8 , in this embodiment the background projector is Sony CX70 Ultra Portable LCD Data Projector, AV Central, Adelaide, South Australia; a target area projector (Sony CX70 Ultra Portable LCD Data Projector, AV Central, Adelaide, South Australia), (target area projector  16 ) projects on to the screen substantially within the target area  8 , a density of visible pixels on the screen such that the target image is at better than eye-limited resolution when viewed by the marksman through the sight  2 , and as will be described in greater detail later in the specification, wherein the contrast ratio of the target area formed by both by the background projector  4  and target area projector  16  is substantially that of the target area projector  16  so as to provide the best possible target image to the marksman. 
     Continuing reference to  FIG. 1 , in this embodiment, a non-visible radiation detector (in this embodiment a laser footprint detector)  18  is directed to detect the target area  8  on the screen  6 . The detector (in this embodiment a Photron PCI 512 Fastcam, Blink Technology Australia, Pty Ltd) for detecting the reflected non-visible laser footprint on the screen is arranged such that the density of the detector pixels for receiving the non-visible footprint and the intensity and size of the laser footprint is such that there is a predetermined accuracy of the detection of the location of the footprint as described in greater detail later in the specification. To determine the parameters of the density of the detector pixels and the intensity and size of the laser footprint requires consideration of the measurement accuracy required for the marksmanship task being trained or assessed. For example, a pass/fail criterion may be the requirement to achieve an extreme spread less than 200 mm when shooting at a target at 100 m on the live range. This would then lead to the requirement to discriminate between extreme spreads over a range encompassing values below and above this pass/fail criterion. This leads to a requirement to be able to discriminate to well below the pass/fail criterion. In this example this could be approximately 25% of the pass/fail criterion (that is 50 mm). The measurement accuracy required to achieve this level of discrimination consequently may be an order of magnitude better than the 50 mm task requirement; that is the detection system would be required to have a measurement accuracy of equivalent to 5 mm on a real target. In a marksmanship simulator, where the marksman may fire at a distance of 10 m from the screen, by geometry (similar triangles), the measurement accuracy requirement in the simulator would therefore be 0.5 mm. 
     The detection process in one embodiment uses a processor  11  which is connected to both the background projector  4 , the target area projector  16 , and in particular the laser footprint detector  18  so as to determine the weapon aim-point of the marksman. It is not necessary for the target area projector  16  to be located adjacent the laser footprint detector  18 , however, the respective projection and detection areas on the screen  6  should be coincident on the screen. There may be some circumstances where these areas do not align for one reason or another, an example being where a portion of the screen needs to be assessed as to whether a laser actually missed the target area. 
     Image Resolution 
     There are a number of ways that a marksmanship simulation arrangement can be achieved using the above elements, but one arrangement is to use a marksmanship training weapon  1  for projecting a non-visible laser footprint onto the screen  6  and a background projector  4  dedicated to projecting the background image and which invariably overlays the target area. The target area projector  16  for projecting target image  19  in target area  8  is superimposed over that portion of the background image  9  which has been generated by the background projector  4 . Other features and advantages can be provided by using one or more other elements such as controlling the movement of the target area within the projected background image while co-coordinating the detection of the target area with the laser footprint detector. 
     The resolving power of the human eye is approximately one to two minutes of arc, and can vary between individuals around that average value. Therefore each pixel in the target area image subtends no more than 1 minute of arc in order for this image to be at eye-limited resolution from the marksman&#39;s viewpoint. This can be achieved by positioning the target area projector  16  relatively close to the screen in comparison to the background projector. Alternatively, the target area projector  16  may be positioned further from the screen, but with an optical device  20  that focuses the whole image onto a smaller area; these arrangements are depicted in  FIG. 2 . The latter solution may be preferred when shooting at targets simulated to be at very long ranges (e.g., 1000 m). These solutions result in the size of the pixels making up the target image to be small enough so as to not be resolvable by a marksman with normal vision when looking through the sight  2 . 
     A further aspect of the invention is the sole use of a detection of the laser footprint on a target image within a target area by a detector  18 . In one detection arrangement, the laser footprint is smaller than the detector pixels and the detector outputs a signal representative of the location of the detected non-visible laser footprint relative to the pixels of the detector. The footprint location can then be used to determine the accuracy of the marksman for a single shot as well as for determining the extreme spread and other performance measures from multiple shots. 
     Various other detection arrangements are also possible, including where the detector pixels are larger than the laser footprint, but detection techniques can still resolve the location of the footprint to an accuracy which allows for single and multiple shot determinations of the marksman&#39;s accuracy within the pre-determined accuracy as described earlier. 
     Details of the arrangement of specific embodiments of the projector/s and detector will be described in greater detail later in the specification. 
     Illustrative of the inaccuracy of prior art,  FIG. 3  illustrates the prior art projection of the background image including the target image to illustrate the limitations in target imagery. 
     A projector  4  generates a background image including a target image  9  on the screen  6 . The target image can be projected anywhere on the screen  6  by the projector  4 . The target image  9  covers only a few projector pixels in the target area  8 . 
     Referring to  FIG. 4   a  the upper image is illustrative of the pixel density of target imagery in the prior art and in the case of  FIG. 4   b  the upper image is illustrative of a representative and comparative embodiment of the invention having a much higher pixel image density than depicted in  FIG. 4   a . The lower images in  FIGS. 4   a  and  4   b  are illustrative of the view of the target image by the marksman either unassisted or assisted by the use of a weapon sight. The lower image in  FIG. 4   a  is a picture of an actual digitally projected image of a target from a prior art simulator and clearly contains visible unwanted artifacts introduced by the pixilated view of the low resolution projected target image of the prior art. No such artifacts are visible in the better than eye-limited resolution target image projected by the target projector in the representative embodiment of the invention. 
     The geometric calculation provided in  FIG. 5  is based on the formula for calculating for the maximum projected pixel size to achieve eye-limited resolution; 
       Φ=2 a  tan [ d /(2 D )]
 
       θ= mΦ= 2 a  tan [ d /(2 D )]
 
     Where m=magnification of the sight
 
D=distance between marksman&#39;s eye and the screen
 
d=maximum distance between the centre of adjacent pixels
 
θ=angle subtended by a pixel as viewed by the marksman and is set to be 1 minute of arc (0.291 milliradians) such that the pixels are at eye-limited resolution
 
     Hence, the maximum size of a pixel (d) for producing a target at eye-limited resolution for a given distance from the screen D is: 
     
       
         
           
             
               
                 
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     Using the above equation for one embodiment of the invention in which D=10 metres yields d=2.91 mm/m. In one embodiment of the invention, magnification m may range from 1 to 10. The target area projector (Sony CX70 Ultra Portable LCD Data Projector, AV Central, Adelaide, South Australia), has a native resolution of 1024×768. Hence, the maximum area that can be projected by the target area projector such that the target image is at eye-limited resolution ranges from 2980 mm×2235 mm (m=1) to 298 mm×224 mm (m=10). In this embodiment of the invention, typical target images are tens of mm across and hence the invention readily achieves eye-limited resolution target imagery. The target area projector is placed approximately 1 metre from the screen and achieves a field of view approximately 0.75 metres×0.6 metres. Hence d is approximately 0.7 mm which yields an eye-limited resolution target image up to a magnification of ×4 for a marksman positioned 10 metres from the screen. Eye-limited resolution target images at greater magnifications may be achieved in an alternative embodiment of the invention wherein an optical device focuses the whole image onto a smaller area; as depicted in  FIG. 2 . 
       FIGS. 6   a  and  6   b  depict a graphical illustration of the light intensity falling along a straight line cross section on the screen in the vicinity of the target image. The maximum contrast ratio that the projection and screen system is capable of producing can be determined by projecting a test image where the light intensities rise and fall through the minimum and maximum intensities across several pixels for the background and target projectors producing a checker board effect on the screen.  FIG. 6   a  left shows the case where only the target projector is projecting this test image onto the screen.  FIG. 6   a  right, shows the case where only the background projector  4  is projecting the test image over the entire screen, and the graph shown in the figure is showing the intensity plot in the region of the target image. For the purpose of this description it is assumed that the target area projector has been dimmed such that the maximum intensity of light falling on the screen is very nearly equal to the light intensity of the background projector. Since the light output of the target area projector is focused into a small area on the screen, the light intensity in the target area will be reduced to match the light levels of the background image where the light output of the background projector is spread over the entire screen. To achieve such balancing between projectors of roughly similar light output capabilities, the target area projector light settings are set low enough to match the light intensity of the background image. If the target area projector does not have sufficient range to achieve this, then a neutral density filter can be placed in front of the target area projector lens to further reduce the light output of the target area projector. 
     The maximum light intensity of the target image ( 6   a  left) is denoted by I maxt  and the minimum light level by I mint . In a similar way, the maximum light intensity of the background image ( 6   a  right) is denoted by I maxb  and the minimum intensity of the background image is given by I minb . The contrast ratio of the target image (with only the target area projector,  6   a  left) is given by I maxt /I mint ; and the contrast ratio of the background image is given by I maxb /I minb . 
       FIG. 6   b  depicts the effect of superimposing images from the background projector and the target area projectors in the area of the target image, where on the left of  FIG. 6   b  both projectors are modulated through their full range of intensities across several pixels.  FIG. 6   b  on the right shows the case where the target area projector is producing light intensities through its full range, whereas the background projector is emitting minimal light intensity. 
     With reference to  FIG. 6   b  left, if the maximum and minimum intensities across a distance encompassing several background projector pixels are taken, the background contrast ratio, R b  is given by: 
         R   b =( I   maxt   +I   maxb )/( I   mint   +I   minb ) 
     However the target contrast ratio can be determined by taking the ratio of maximum and minimum intensities over a smaller distance, encompassing a distance that contains only several pixels of the target project. With reference to  FIG. 6   b  left, in the regions of 25 mm, 35 mm, 45 mm (where the maximum light intensities of the background projector occur), the contrast ratio is given by: 
         R   tmax =( I   maxt   +I   maxb )/( I   mint   +I   maxb ) 
     With reference to  FIG. 6   b  right, where background projector  4  is producing minimal light intensity, while the target image projector is producing its maximum contrast the contrast ratio is given by: 
         R   tmin =( I   maxt   +I   minb )/( I   mint   +I   minb ) 
     For the purposes of illustrating the concepts of contrast ratio and without loss of generality, if the two projectors were of matched brightness and contrast specifications and the intensities of the target and background images on the screen were matched by use of a suitable light filter placed in front of the target area projector, then I maxt  and I maxb  can be replaced by I max  (I max  being the maximum screen intensity that can be produced by each projector). Similarly I mint  and I minb  can be replaced by I min  (I min  being the minimum screen intensity that can be produced by each projector). The contrast ratio equations then become: 
         R   b =( I   max   +I   max )/( I   min   +I   min )=(2 I   max )/(2 I   min )= I   max   /I   min    
     That is the contrast ratio over several background pixels is for the intents and purposes of this disclosure, approximately equal to the contrast ratio of each individual projector pixel. 
     However, the contrast ratios across a few target image pixels are given by the following equations. In the region where the background image projector is producing a maximum intensity the contrast ratio is: 
     
       
         
           
             
               
                 
                   
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     In the region where the background image projector is producing a minimum intensity the contrast ratio is: 
     
       
         
           
             
               
                 
                   
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     Typical contrast ratios of projection systems in a darkened room can be of the order of 500:1 or greater. For the purposes of illustration consider the case of using background and target area projectors that both have contrast ratios R of 500. The contrast ratio performance across the region of several background projector pixels is given by R b  and is thus  500 . That is the use of two projectors does not adversely affect the contrast achievable over several background pixels or greater. 
     However, taking the illustration further, the target image contrast ratio in the region of maximum background intensity is given by: 
         R   tmaxb =2/(1 /R+ 1)=2/(1/500+1)≈2 (since 1/500 is much smaller than 1)
 
     That is an R tmax  of two implies that the high resolution detail from the target image is washed out by the low-resolution of the background projector if the light intensity of the background projector is high in the target image area. The contrast ratio in the region where the background projector is generating minimum intensity is given by: 
         R   tminb =½( R+ 1)=½(500+1)=½ R≈ 250
 
     Hence by using two projectors although a higher spatial resolution can be achieved in the target image, the contrast ratio is, in the best case halved, and the requirement to achieve this performance is that the background projector must produce minimal intensity and contrast in the region of the target area. 
     Hence in selecting projectors the simulation engineer should select a background projector that has specifications for producing regions of black that emit the lowest level of light possible. However because the target projector has its light output concentrated into a small region of the screen, the maximum brightness specification of the target projector is less critical, but because of the contrast ratio of the target image is diminished by the light leaking when the background projector is emitting “black” the target-projector would benefit by having a better contrast specification than the background projector. 
     In another embodiment of the invention which does not include a screen or background projector, a marksmanship simulator for the training of a marksman having a marksmanship training weapon for projecting a non-visible radiation footprint can include, a target area image capable or reflecting non-visible radiation. In one specific example this could be a printed photographic image of a target (an inanimate target) which is located a distance from the marksman. In one arrangement the target could be at a similar distance to the target image used in other embodiments. 
     In this arrangement the detector for detecting the reflected footprint on the target includes a density of detector pixels for receiving the non-visible footprint, and the intensity and size of the non-visible radiation footprint is such that there is a predetermined accuracy of the detection of the location of the footprint. 
     In the above embodiment the marksmanship simulator includes a means of illuminating the target. Illumination could be non-visible light for night marksmanship training usable in conjunction with night vision systems by the marksman. Further radiation in the visible range can be used to increase the visible intensity of the target during simulated daytime marksmanship training. 
     Hit Detection 
     Modern small arms simulators rely on a single hit-detection camera  20  to detect the laser footprint  7  anywhere over a wide area of the screen  6  as depicted in  FIG. 7 . In some cases, where systems allow multiple firers, several cameras may be employed for the same purpose (e.g., multiple cameras for multi-lane systems). The position of the laser footprint is then correlated to the position of the target. The hit-detection system sees the screen as a set of distinct blocks, as pictorially represented in  FIG. 7 , each block typically referred to as a pixel  14 . In this instance, each pixel represents the projection of the camera sensory elements onto the screen (as distinct from the pixels of the projected imagery). 
     Typically a computer associated with the hit-detection sensor forms the hit-detection system, and uses the detected intensity and coordinate position of the detection pixels illuminated by the laser footprint ( 7  in  FIG. 7 ) to calculate the laser footprint position and hence the weapon aim-point. The accuracy of this calculation is dependent on three factors; the size of the detector pixels for receiving the non-visible footprint and the intensity and size of the laser footprint. This is illustrated in  FIGS. 8   a ,  8   b ,  8   c ,  9   a ,  9   b  and  9   c  which demonstrate different examples in which these three factors are varied. 
       FIG. 8   a  shows the case where the size of the laser footprint is larger than that of each detector pixel. In this case, the hit-detection system will calculate the laser footprint position by determining the footprint centroid which is the intensity weighted average of the coordinate positions of each pixel, where the intensity at each detector pixel includes contributions from the laser footprint and from noise (internal to the camera as well as background thermal noise). Consequently, the accuracy of this calculation is determined by the signal to noise ratio in the detection process which is predominantly affected by the intensity of the laser footprint.  FIG. 8   b  shows the case where the signal to noise ratio is low and consequently the centroid calculation is biased by noise and is inaccurate. When calculating the centroid, a threshold can be applied to reduce the effect of noise. However, in this case, the application of a threshold is not sufficient to completely eliminate the effect of noise because the intensity at each detection pixel illuminated by the laser footprint has a significant contribution from random noise as well as from the laser footprint.  FIG. 8   c  shows the case where the signal to noise ratio is high and consequently the centroid calculation is not biased by noise; application of a threshold can substantially eliminate the effect of noise and results in more accurate determination of the centroid of the laser footprint.  FIG. 9   a  shows the case where the size of the laser footprint is smaller than that of each detector pixel and in most instances, the laser footprint illuminates a single pixel. In this instance, the hit-detection system calculates the laser footprint position to be that of the single illuminated pixel and the accuracy of the calculation is determined by the size of the detector pixel. As shown in  FIGS. 9   b  and  9   c , the effect of noise is less significant because the illuminated pixel can be uniquely determined after application of a suitable threshold. 
     In a modern small arms simulator, the hit-detection is performed by a standard charge-coupled device (CCD) camera; the CCD cameras employed typically have a resolution of 760 pixels (horizontal) by 580 pixels (vertical). For a system allowing a quartet of firers, the screen dimension is such that the pixel (as seen by the camera) is a square on the screen of approximately 4 mm on each side. The size of the laser footprint in modern small arms simulators is considerably larger than this, around 10 mm in diameter. This corresponds to the case shown in  FIG. 8   a  above and consequently, the size of the pixels does not limit the accuracy of the hit-detection calculation. The determining factor is now the signal-to-noise ratio. 
     To overcome the problem of poor signal-to-noise ratios that characterizes the prior art, the following solutions are proposed: (1) a hit-detection camera that is positioned so as to capture the area of the screen immediately surrounding the target (in order to increase the amount of signal captured relative to the areas not covered by the signal which simply add noise to the centroid calculation), (2) hit-detection cameras that have noise floors superior to those used in the prior art and (3) an eye-safe laser that has a higher intensity and smaller footprint than those used in the prior art. One embodiment of the current invention utilizes all three of these solutions to achieve superior signal-to-noise ratios and hence highly accurate weapon aim-point calculation. 
     In addition to adequate signal-to-noise ratio, it is important that the weapon aim-point calculation is not adversely affected by the large size of the detector pixel (both in absolute terms and relative to the laser footprint). The size of each detector pixel is determined by the dimension of the screen captured by the CCD camera relative to the camera resolution. Consequently, the pixel size can be reduced by increasing the resolution of the camera or capturing a smaller area of the screen. In one embodiment of the current invention, the hit-detection camera only captures a small area of the screen in order to maximize the signal-to-noise ratio. In this case, the pixel size is small and the effect is negligible, regardless of the size of the laser footprint. This is illustrated in  FIG. 10  which shows the preferred arrangement of the use of one hit detection sensor (camera) directed to the target area (the finer grid area central to the upper right illustration in  FIG. 10 ). These aspects of the invention are further illustrated in  FIGS. 11   a ,  11   b ,  12   a  and  12   b .  FIG. 11   a  shows the case where the size of the laser footprint is larger than that of each detector pixel;  FIG. 11   b  shows the calculation of the position of the laser footprint.  FIG. 12   a  shows the case where the size of the laser footprint is larger than that of each detector pixel;  FIG. 12   b  shows the calculation of the position of the laser footprint. 
     It should be apparent from the preceding discussion to one skilled in the art that there is no simple equation which determines the accuracy of a particular embodiment of the hit-detection system as illustrated in  FIG. 10 . The accuracy is determined by the detector pixel size, the size and intensity of the laser footprint and the signal-to-noise characteristics of the detector. There is a range of values for these parameters that satisfies the weapon aim-point accuracy requirement which was described earlier in the specification and simulation and experimentation are required to precisely determine the accuracy of a given embodiment of the invention. However, appropriate choice for these parameters allows the design of an embodiment of the invention that has a pre-determined accuracy that satisfies the weapon aim-point accuracy requirement which was described earlier in the specification. 
     In one embodiment the camera (Photron PCI 512 Fastcam, Blink Technology Australia, Pty Limited) with a resolution of 512×512 pixels is placed approximately 2 m from the screen and captures an area approximately 0.25×0.25 m. This results in a pixel size of approximately 0.5 mm. 
     With regards to the firing weapon the radiation emitted is preferably non-visible, and can be infra-red or preferably laser, since the smaller laser footprint provides for increased accuracy, in this embodiment the laser is an eye-safe infra-red laser (LDM-5-850-0.78, from Laserex Technologies). In one form, the laser is attached to a suitable weapon and is fired at the screen from a distance of 10 m. 
     An infrared light filter (Andover 830FG07-165S, Lastek Pty Ltd) is attached to the camera such that only radiation from the laser footprint is detected by the camera. 
     The laser footprint provided by the laser (LDM-5-850-0.78) is approximately 4 mm in diameter. Through the use of simulation methods, it may be shown that the relative sizes of pixel (0.5 mm) and laser footprint (4 mm) the maximum error in the calculation of the laser footprint position is approximately 0.1 mm. This is similar to the case shown in  FIG. 8   a  but the pixel is considerably smaller than that of the prior art. By geometry, if the screen is 10 m from the firer, and the simulated target is at 100 m, the corresponding error is 1 mm, which exceeds the weapon aim-point accuracy requirement which was described earlier in the specification. 
     The combination of laser (LDM-5-850-0.78), camera (Photron PCI 512 Fastcam) and filter (Andover 830FG07-165S) results in signal-to-noise ratios of around 60 dB which is of such magnitude that random noise will have minimal impact on the accuracy of the calculation of the laser footprint location. Experimentation with this embodiment of the invention has shown that when the laser is fired from 4.5 m (want 10 m), the hit-detection system calculates the location of the laser footprint to an accuracy equivalent to a radial standard deviation of 0.01 milliradians. 
     Control of the shape of the laser output from the marksmanship training weapon could include the addition of a focusing lens arrangement on the laser  3  to focus the near parallel rays of the laser  3  to as small a spot on the screen as possible. In cases where the size of the laser footprint requires reduction this could be achieved by use of an aperture of suitable size in the barrel  3  to restrict the width of the laser beam and so produce a controlled spot size on the screen  6 . 
     Referring once again to the embodiment of the invention presented in  FIG. 1 , data from the laser footprint detector  18  is made available to the computer  11  for processing. A variety of calculations can be performed by the processor, including displaying either on a separate monitor or on the screen  6  as required the strikes achieved by the marksman, group calculations and many other details relating to individual strikes, timing of strikes, comparison with prior results achieved by the particular marksman or other marksmen. The data can be stored for later retrieval as required. 
     In one embodiment the hit detection process includes the following steps as illustrated in  FIG. 13 , which where required, is processed in an appropriately programmed general purpose computer, having a processor chip, memory and various input and output mechanisms for receiving, storing and sending data related to the marksmanship simulator arrangement and marksmanship detector arrangement. Processes  2  to  13  illustrate the case where there is a single hit-detection camera as in the embodiment of the invention described by  FIG. 1 . If there is a requirement for a second hit-detection camera (if for example, there is a requirement to capture an image of the entire screen) then the additional processes  15  to  23  are shown in order to illustrate how the processing can be replicated and integrated with that of steps  2  to  13 . 
     The processor can provide records (immediately and after a series of shots) of the laser strikes in tabular and graphical form (digital for viewing and hard copy), the presentation of which is arranged to be suited to the training and qualification of marksmen using the simulator arrangement. 
     Step  0  occurs prior to the simulator being run in real time and in this step the entire system is calibrated in order to (1) determine the appropriate scaling factor which scales distances from a reference coordinate system (such as the screen) to the desired coordinate system (such as the firing range being simulated) (2) correct for keystoning and rotation errors resulting from the field of view of the camera being offset and rotated relative to the laser footprint. 
     Radiation (including the laser footprint as well as the background and target images) is reflected from the screen ( 1 ), and strikes infrared light filter ( 2 ). Infrared filter ( 2 ) blocks out the visible portion of the radiation and passes only the infrared component of that radiation, which should now be only that from the laser ( 3 ). The detector camera ( 4 ) now converts the radiation into a pixel image which is an array of values of infrared light intensity ( 5 ). An intensity threshold ( 6 ) is applied to this array of values and sets all values below the threshold to zero, resulting in an array corresponding to the laser footprint against a black background ( 7 ). The processor now computes the centroid ( 8 ) of the laser footprint by taking the intensity weighted average of the (x,y) coordinates of each pixel in array. One method to compute the inset aim-point ( 9 ) would be to apply an equation of the form: 
     
       
         
           
             
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     The processor then scales ( 11 ) the centroid coordinates into the scale of the screen coordinate system ( 12 ) and then displaces this value ( 13 ) according to the offset giving the centroid location relative to a reference coordinate on the screen ( 14 ). The coordinates ( 14 ) now becomes an input into ballistic and fall-of-shot computations. 
       FIG. 13  also shows optional processes  15 - 23  which illustrate how the processing can be replicated and integrated with that of steps  2  to  13  where it is desirable to detect the footprint outside of the target area in order to give a low-resolution indication of the extent to which a shot missed the target area. 
       FIG. 14  depicts the intensity level of the pixel array in one of the axes before applying a threshold. 
       FIG. 15  depicts the same pixel intensities as shown in  FIG. 14  after the application of the threshold where values below the intensity threshold are set to zero. 
       FIG. 16  depicts the geometry of the scaling and corrections applied to the centroid in the detector coordinate system in order to convert them to screen coordinates. 
       FIG. 17  depicts the output provided by the processor as feedback to marksman and instructors. Performance data is displayed as the calculated fall-of-shot after ballistics calculations have been applied to the location of the laser footprint. As an example,  FIG. 17  displays the fall-of-shot and extreme spread value for a marksman shooting  5  rounds at a target.