Alain <kua### [at] videotronca> wrote:

> > I've been experimenting with creating lightprobe images for space scenes, using
> > a combination of GIMP and PoVRay.
> >
> > The process is pretty straightforward: I begin by creating a space scene as a
> > cubemap in GIMP, I then import the map as a png into a custom model in povray,
> > and render using a spherical camera at an aspect ratio of 2:1 (4000x2000) with
> > output set to +FE.
> >
> > The only problem I see with my image is that the stars may be a little too
> > dense, or too large, to be realistic when mapped onto the cube.
> >
> > The real problem I'm having is that I can't seem to get the EXR image to map
> > back onto a sphere properly.  It's always very distorted.
> >
> > I've uploaded the relevant files to my dropbox, since they're a bit large for
> > uploading here.  If anybody can tell me what I'm doing wrong, I'd appreciate it.
> >
> > https://www.dropbox.com/sh/gj5khxb2nqg02kx/AABGsc5rP7PX34sUk3ExJkZFa?dl=0#/
> >
> > Regards,
> > A.D.B.
> >
> >
>
> As your image is intended to be mapped onto a box, mapping it to a
> sphere, using whatever method, can only introduce some distortion,
> specialy near the vertices.
>

I figured this was the problem, but it didn't occur to me until long after I'd
posted the question.

> Start by UV mapping your image onto box{-1, 1}. Your original image have
> exactly the right cross shape for that purpose. The image is intended to
> be used with the camera at <0,0,0>.
>
> Scale that box large, something like scale 1000 or more. The exact
> scalling depend on the dimention of the scene where you intend to use
> your sky.
> It's best to place the camera at the origin to prevent introducing
> further distortions.
>
> This should take care of any distortion.
>
> As for the stars been to large, you'll need to keep them the same size,
> but make the image larger.
>
>
> Alain

Thanks for the advice.

Regards,
A.D.B.

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