LOD calculations

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Renee Maheshwari (mahe0010++at++gold.tc.umn.edu)
Thu, 18 May 1995 16:38:28 -0500 (CDT)

I am wondering how channel size affects how Performer calculates LOD range
for a predefined object with LOD ranges. I have the following information:

>Inside Performer for LOD switching,
>
> true range = (defined range) * (Lod Scale) * (Global Lod Scale)
>
> defined range is assumed to be for 1280x1024 at 45 Degree FOV
>
> Lod Scale is a multiplier calculated from channel size & actual FOV
          /\
Lod Scale || is what I have my question on...

> Global Lod Scale is a global value per channel that is applied to all
> LOD's

The part below is the part I'm wondering about, which determines the
Lod Scale---what are horz and vert on the
right hand side of this equation??? Are they field of view? I'm assuming that
xs and ys are the x and y channel size, but I may be wrong on that too.
Also, is this horz and vert defined recursively, or is that some typo?

> /* this came from the Performer Team and is how a channel size */
> /* affects the Lod Calculation */
> horz = (xs * 0.5f) / pfTan(horz * 0.5f);
> vert = (ys * 0.5f) / pfTan(vert * 0.5f);
>
> max = PF_MAX2(horz, vert);

What is TAN_MPI8?????

> lodAspect2 = (512.0f / TAN_MPI8) / max;
>
> Lod Scale = (FOV/45) * (lodAspect2)

        Thanks in advance for any help
                Renee Maheshwari
                mahe0010++at++gold.tc.umn.edu

         

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