> I am currently working on a UTD MOM hybrid solver.
> This is a solver for an electromagnetic waves that uses an hybrid method 
> between
> geometrical optics and direct solving of the maxwell equations.
> In the part of the geometrical optics I am planning to use direct ray 
> tracing
> (source to camera/point of measurement).
> My brother suggested I consult this website, and use parts of the ray 
> tracer as
> a base for my program.
> I have encountered a problem understanding direct ray tracing.
> Unlike in backward ray tracing, the number of rays entering every pixel is 
> not
> fixed (depends on the geometry and the density of the incoming rays).

A ray travels from the camera and strikes an object. That object then cast 
rays
in the direction of the light sources, and if the lights are unobstructed 
the
color is determined by phong and/or specular highlight models and object 
color.
The object could be reflective and/or transparent though, if so then a ray 
is
traced from the object at the proper angle and travels on to strike a second
object... etc. This process is repeated until max_trace level is reached, or
the contribution of the next object would fall below the adc_bailout value.
This final value then becomes the resulting pixel value at that spot.

> Say I double the incoming ray density so I will get a double number of 
> rays
> hitting every pixel, but the actual number of rays is dependent on the
> geometry.
> So how do I normalize the value inside the pixel?
> Any one knows a good forward ray tracing tutorials that could help me?

POV can use adaptive anti-alias super-sampling of pixel values.
Anti-aliasing is adaptive: it will only super-sample pixels that are 
different
in color from neighboring pixels. The threshold value controling
the trigger for perfoming super-sampling on a pixel is suplied by
the user though, so it can be set very low if required.
In general higher levels of anti-aliasing result in a squared increase in
the number of rays cast from the camera, though the actual number
can vary by method.
Search the documentation under "+a" for more details.

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