Does this help? https://gfycat.com/ShabbySeriousDrafthorse
On Sun, May 15, 2016 at 7:02 AM, Matt Lind <[email protected]> wrote: > I would need to see the problem to give a good answer as I'm not sure what > I'm envisioning in my head matches what is being described. > > Knowing how the sphere is modified is important. Unfold tries to evenly > distribute the texture space of the texture to match the topology while > minimizing stretch/compression. If the poles have elongated triangles, > then that will obviously play into the distribution of the unfolded texture > (in theory it shouldn't, but in practice it does). One way to mitigate > that > issue is to add vertices and perpendicular edges at regular intervals along > the elongated edges to closely match the spacing of other edges around the > rest of the mesh, but that will have limited influence on the result and is > more of a brute force technique. > > Unfold is also a flawed tool as even simple cases come out distorted. for > example, get a primitive sphere and imagine it's the Earth. Place a > vertical UV seam down one side at the international date line, then two > more > seams at the arctic/antarctic circles. Deselect the vertical edges > connecting the circles to the poles. Now unfold the mesh. Notice the > sphere is splayed in butterfly fashion, but one half is larger than the > other and slightly off kilter in alignment with the texture editor. The > circle at one pole is often (but not always) larger than the other circle > too. These are the kinds of issues you'll battle, but on more complex > cases > they'll be too complex to solve without resorting to cleanup via > pushing/pulling points to correct the flawed parts of the unfold. > > However, let's put all that aside and look at the goal from the beginning > and not the current situation which has a roadblock. > > An equirectangular projection comes in a few flavors, but most are similar > to a cubic projection. The main difference is in how the top and bottom > sides are projected. Simple analysis of the problem would suggest one > could > take a cube and use Catmull-Clark subdivision smoothing to round it into a > sphere. That would accomplish nicer edge placement which closely match the > meridians of the projection to handle (or fabricate) the texture space. A > single vertical seam from pole to pole (despite no physical poles) could be > used to unfold and splay the sphere to accept/define the projection, but > subtle details may need to be tweaked for a perfect match. > > Alternately, use rendermap applied to a sphere to capture the external > world. The rendermap generated image should mimic an equirectangular > projection. You may have to open the poles like the Earth without the > arctic/antarctic circles, for example, to adjust the field of view for the > rendermap process. Invert the sphere's normals so rendermap points > outwards > into the world instead of inwards towards the sphere's surface....and of > course, exclude self or make the material 100% transparent so it doesn't > block the rendermap camera from seeing the world. Since rendermap travels > texel-to-texel along the geometry, a high resolution image and smooth > surface are really important. I'd encourage you to use a NURBS sphere with > view dependent smoothing for best results. you set those in the sphere's > geometry approximations PPG. Try setting length/distance/angle values to > less than 2 degrees and 0.5 units, activate view dependent subdivision > smoothing, and make sure the min/max subdivision limits are increased > beyond > the default 1,3 (well, just the max. shouldn't have to go beyond 6). If > you get sawtoothing at the poles or faceting artifacts in the resulting > texture, then it means your smoothing parameters are not set correctly. > The > reason for using NURBS over polygons is the better interpolation of the > shading normal between texels. Rendermap is highly dependent on the > shading > normal orientation to determine what it's camera points at. When pointing > a > camera into the outside world, even very tiny deviations in normal > orientation can produce big errors in the result. NURBS are infinitely > smooth whereas polygons are only as smooth as they are subdivided - and > even > then approximations at best. > > Matt > > > > > Date: Sat, 14 May 2016 17:33:32 +0200 > From: "Sven Constable" <[email protected]> > Subject: RE: equirectangular uv > To: <[email protected]> > > 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 [email protected] > with "unsubscribe" in the subject, and reply to confirm. > -- *------------------------------[image: http://i153.photobucket.com/albums/s202/animatics/probiner-sig.gif]Pedro Alpiarça dos Santos >> http://probiner.xyz/ <http://probiner.xyz/> <http://probiner.x10.mx/>*
------ Softimage Mailing List. To unsubscribe, send a mail to [email protected] with "unsubscribe" in the subject, and reply to confirm.
![http://i153.photobucket.com/albums/s202/animatics/probiner-sig.gif]Pedro](http://i153.photobucket.com/albums/s202/animatics/probiner-sig.gif]Pedro){kind=link}