"Chris B" <c_b### [at] btconnectcomnospam> wrote in message 
news:43cbaf44$1@news.povray.org...
>
> "shimon_a10" <shi### [at] wallacoil> wrote in message 
> news:web.43c92e281fd85402981d861f0@news.povray.org...
>> hi,
>>
>> I'm a beginner at PovRay,  and i wanted to ask:
>>
>> 1. I'm making an image by making Box,plane,etc, and putting the camera in
>>   somewhare at world coordinte.
>> 2. I wanted to know how to relate an arbirary pixel in the image to the
>>   world coordinate (x,y,z) that it's see.
>> 3. If it possible to write me the prcedure.
>> 4. please answer me in detail.
>> 5. Lots of thanks.
>>
>> shimon
>>
>
> Hi Shimon,
>
> The default camera is a perspective camera that acts like a pinhole 
> camera. The image is constructed by tracing straight lines from the point 
> of the pinhole (the position of the camera) through points on the image 
> plane and on until they hit something (or not). The image plane is 
> perpendicular to the direction the camera is looking in, which is 
> controlled by the camera definition.

> The distance from the camera is defined by the direction vector and 
> defaults to 1.

I should have said 'The distance of the image plane from the camera is equal 
to the length of the direction vector which is equal to 1 when using the 
default direction vector'.

>
> This is explained more comprehensively (with a diagram) in section '3.3.1 
> Camera' of the POV-Ray help files.
>
> So for a given pixel and a known camera definition you can calculate the 
> equation of the line along which the ray was traced, but, from the image 
> pixels you can't determine the point along that line at which it 
> intersected an object (if that's what you're asking in 2.)
>
> Chris B.
>

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