I created this surface by draping a surface ontop of a mesh, which created the surface on the right (in the viewport). When I rendered it, I get these weird lines on the surface. Does this have something to do with my render mesh quality and if so, what numbers should i be looking to change to create something more smooth? As you may have guessed it is indeed a topo for a canyon, so the change in elevation is drastic (close to 200 meters).
Any help is appreciated!
~Matt
Re: Weird Lines on Rendering
These are mesh artifacts that are showing up. Did you use MeshDrape or did you Drape a nurbs surface and then extract the mesh? I think if the mesh could be smoothed a little bit, then it would be better, but getting to a mesh smoothing algorithm in Rhino takes just a little bit of digging. Below is a link to a plugin called Shut Lines…load that plugin and it should expose a command called CatmullClark…running that on the mesh will smooth it and hopefully prevent those edges from showing up.
http://news2.mcneel.com/scripts/dnewsweb.exe?cmd=article&group=rhino&item=296512&utag=
Re: Weird Lines on Rendering
Thanks Damian! Will give it a shot to try to see if it works. I did actually have a mesh that I then NURBS draped overtop. I then deleted the mesh and that’s what I was left with.
Re: Weird Lines on Rendering
Damien, should this lines not invisible allways? OK, smoothing maybe a workaround, but if the mesh polycount is ok for the rendering, than it should be rendered without lines. Or could one of the mesh (repair) tool help?
Re: Weird Lines on Rendering
I’m not sure why these lines show up. I think they may be due to extra mesh faces being created between those two verts or having very messed up texture coordinates. If the first one is the issue than most likely the Catmull Clark Subdiv won’t work, so that will be a clue. Ultimately, this situation bites because Rhino doesn’t really have enough mesh tools to identify the issue or deal with it, so we just got to make due with round about shots at resolving it. I don’t like more polys either, but I’m not sure what else to suggest.
Re: Weird Lines on Rendering
Matt, if you like you could post the mesh (f.ex. per rapidshare.com).
Re: Weird Lines on Rendering
Thanks again for taking the time to check this out. This file has both the mesh that was imported from 3ds max as an .obj file (and subsequently came in as a mesh) but also the draped nurbs surface that was draped over top the mesh creating a new surface.
http://rapidshare.com/files/245698703/Laureles\_Topo.3dm.html
Many thanks!
~Matt
Re: Weird Lines on Rendering
The lines will be less visible, if the sun shadow bias is set higher - I tried 1. I set the secondary ray bias (global switches) at 1 too and now all mesh lines are gone. 
Both bias settings at 0.1 works too. I’m not sure what the best value is, but I would try to keep the valuea low.
But general the mesh looks quite ugly for me, thin triangles everywhere caused shading artefacts. I would try per the free software meshlab to get a better mesh.
Re: Weird Lines on Rendering
The highest practical value for secondary ray bias is .01 any more than that and that can cause significant artifacts in a variety of places.
Re: Weird Lines on Rendering
Thanks again Micha and Damien! This is really the first time I’ve worked with meshes in Rhino because of these exact issues, so I thought that give it a shot.
Many thanks for your thoughts and suggestions.
Re: Weird Lines on Rendering
Damien, I’m curious for the CatmullClark smooth function, but can’t find it. Is it the right plugin?
Re: Weird Lines on Rendering
It’s the right plugin and I found the command, but it wasn’t working with my mesh.
