[Radiance-general] obj2mesh proposal [was: obj2mesh, UV coordinates and image aspect]

[Thomas Bleicher]

Forget that! See the other post and the solution by Greg.

Thomas


On 20.02.2006, at 17:51, Thomas Bleicher wrote:

> Hello group, hello Greg ;)
>
> My recent experiments with obj2mesh and uv coordinates have
> inspired a proposal to add uv coordinate conversion to
> obj2mesh.
>
> The problem:
>
> Radiance works in a texture coordinate system of (Lu,Lv)
> where the _smaller_ dimension is 1.0 and the larger is >1.0.
> Other file formats (especially *.obj) work in a texture
> spaces that's normalized to 1 (both dimension are in the
> range (0,1) regardless of width and height of the image).
>
> When uv coordinates are present in an *.obj file that's
> converted via obj2mesh the coordinates are taken as they
> are found which is only correct for square images. In other
> cases only the lower left square of the texture image is
> used for the mapping.
>
> Current solution:
>
> The uv coordinates of the *.obj file have to be converted
> to the range expected by Radiance before the mesh is created
> with obj2mesh. This is not difficult but it would change the
> content of the original file in a way that's probably against
> the specs of the *.obj file format.
>
> Alternative:
>
> My proposal is to add a new option to obj2mesh to set the
> aspect ratio of the texture image when the mesh is created.
> obj2mesh can do the necessary conversion of the normalized
> uv coordinates and write the converted values to the mesh.
>
> The informations necessary are the relation of the image
> dimensions and which side is the larger one (w or h). Both
> can be given in a single float when we assume a w/h aspect
> of the images (though I'm not sure this convention exists
> anywhere in Radiance). The default should be a 1.0 aspect
> so the current behavior is preserved even without the new
> option given.
>
> Since '-a' and '-r' are already used in obj2mesh the new
> option could be '-t' (for texture aspect). Example:
>
> $ obj2mesh -t 0.5 input.obj output.rtm
>
> to map the uv coords of the *.obj to a landscape texture
> image (eg. w=200 h=400 px).
>
>
> Please correct me if anything is wrong with this idea or
> if it's incompatible with the current use of obj2mesh.
>
>
> Thomas
>
> PS: I may have difficulties replying to emails in the next
>     days or weeks. Please don't think I'm avoiding the wrath
>     if a reply takes a some days.
>
>
>
>
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