> 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.

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

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