Re: pfEarthSky with off-axis viewing frustra

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Christopher R Volpe (volpe++at++ash.crd.ge.com)
Mon, 14 Apr 1997 14:54:12 -0400

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Gan Wang wrote:
>
>
> By rendering coordinates, I mean the coordinates in which the channel eyepoints
> are calculated and the database is loaded. pfEarthSky is rendered in this
> coordinate and is always render with its horizon line perpendicular to the z
> axis. However, the geometry in the database can be computed in another
> coordinate system (i.e., geocentric) and that's when the coordinate
> transformation is needed so that its horizon will be parallel to that of esky.
> I don't think (I could be wrong) that a channel offset (it sounds like what
> you do) will affect anything because that is only a view offset and doesn't
> change the coordinates.
>
> PfEarthSky would still not work well if your eye point is high up in the sky,
> then you would need a true geocentric earth sky, something you have to do
> yourself.

I can see geocentric scene graphs causing a problem with pfEarthSky, but
I don't see how this has anything to do with the manual's warning
against (specifically) off-axis viewing frusta. This sounds like a
completely separate and unrelated problem. If I have a flat-earth z-up
terrain database, why, and under what circumstances, would an off-axis
viewing frusta cause a problem? This still is not clear.

thanks,
Chris

--

Chris Volpe			Phone: (518) 387-7766 
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