Hi all,

oh well... I know it is confusing... I'm not really sure on how to 
present the whole stuff clearly as the software is quite complicated...

Let's start from the beginning, I'm going to test a vision based 
positioning system with both simulation and in the real world 
environment. The past experience of using this system is quite accurate.

For now, I have to develop an augmented reality application, which use 
this positioning system as the base to get the user's location in the room.

The simulation is to test the accuracy of this system, as an "ideal" 
environment. It is because this system hasn't been tested properly 
before. But surprisingly, the result of the simulation is very inaccurate.

Before doing the test, the camera has to be calibrated first so that the 
software collects the lens properties of the camera. These properties 
are responsible for those complicated matrix transformation in 
calculating the camera position from those markers. And the coordinate 
of the marker (the 4 centroid coordinates of the 4 regions in the corner 
of each target) is supplied to the software so that it can calculate 
those transformation.

Therefore, (as I am the one who know the system most) I think the camera 
definition is not the major problem (maybe I'm wrong). And by posting 
(and looking at) these two images, I think the problem is about the 
markers aspect ration. As Tim Nikias suggest, the povray unit shouldn't 
be the problem. By putting those markers in the same "distance" away 
from the camera, it seems the one generated by povray is really 
distorted (taller and thinner). (since the target dimension has to be 
supplied into the software) And therefore I think this is the major problem.

Here is the camera definition:

camera
{
    location <61.5, 74.55, -200>
    direction <0, 0, 1.7526>
    look_at <61.5, 74.55, 0>
}

The output image is rendered to 384x288 (which is the same aspect ratio 
as the default povray camera ratio). And here is the texture mapping 
code, which simulate a marker that has printed on an A4 size paper:

box
{
    <0, 0, 0>, <21, 29.7, 0.01>
    pigment
    {
       image_map{png target_file once interpolate 2 map_type 0}
       scale <21, 29.7, 0.01>
    }
}


By ignoring the complicated positioning software, did I do anything 
wrong on simulating an A4 sized paper and the texture mapping bit?


Thanks for the attention and sorry for the confusing post before. I hope 
I have make this issue clearer now.

Regards
Colin

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