Implicit simply means the texture is projected without explicitly defined UV coordinates per polygon. Like using a slide projector to project the image onto a surface. That's why it's confined to the basic texture projection types as the method to project the image onto the surface needs to be defined as an algorithm. The advantage is polygon surfaces can get more granular/precise placement of texels because normally they rely on normals and UVs defined at the vertices and interpolated across the polygon for placement which gets less accurate the larger the polygon is relative to the texture space coverage. That is independent of an equirectangular projection mapping method which Softimage does not have by default (other than spherical mapping).
I don't think it's strictly a mental ray feature, but even if it were, any surface attribute produced by mental ray can be captured using rendermap/ultimapper/lightmapper and exported where needed. You may be able to build your own projection using ICE, but a mental ray shader would produce better results as it has the advantage of the subsampling and interpolation methods available in the renderer which are significantly higher quality and more granular than anything ICE has access to. Developing a shader would also be easier. I conducted an experiment by applying Catmull-Clark subdivision smoothing to a cube, applying a spherical texture projection, then rendermapping the result. After that, I created my own spherical mapping shader in the rendertree using the available nodes, applied it to the cube, then rendermapped that too. Comparing the results side by side revealed some broken internals of Softimage. As it turns out, the default spherical mapping as seen in the viewports is all F****d up, but if you rendermap that projection, the resulting image will be perfectly clean without distortion at the poles. Conversely, my self-devised spherical shader built in the rendertree looked perfect in the viewports/render region, but rendermap captured distortion at the poles equivalent to what you see in the viewports with the default spherical projection. Apparently the viewports and rendermap use different algorithms for the same work. Getting back to the original question - the fact you see garbage at the poles of the sphere in the Softimage viewports should be of no concern because it's isolated to the viewports and should not transfer to Unity or whatever engine you're exporting your stuff. Equirectangular projections created with Rendermap will come out clean. Matt Date: Sat, 14 May 2016 17:33:32 +0200 From: "Sven Constable" <sixsi_l...@imagefront.de> Subject: RE: equirectangular uv To: <softimage@listproc.autodesk.com> To fix distortion on the poles, XSI has a special mapping feature called 'implicit' (Clusters/?Texture Projection Def), but this is actually a mental ray feature and doesn't deal with UVs at all. So when exporting meshes you cannot use it, I think. I'm not familiar with Unity unfortunatly, maybe there is a similar feature for spherical projections not using UVs but instead a special projection method (perfect spherical) ? Otherwise, since a sphere always has poles/singularities you will get distortions on them. Workaround could get rid of the poles by deleting the inmost polygons on each pole, duplicating the resulting (open) edge loop, and scale it to zero. Resulting in many point on the same spot. Then relaxing them in the texture editor. Results could be ok, not sure. Maybe I'm overcomplicating it. Matt Lind needs to chime in :) Can't you use cubic mapping? That should avoid the problem in the first place. sven ------ Softimage Mailing List. To unsubscribe, send a mail to softimage-requ...@listproc.autodesk.com with "unsubscribe" in the subject, and reply to confirm.
