Displacement artifacts

[sboerner]

I've been running into artifacts along displaced edges. They occur with procedural and image displacements, and show up as the displaced surface approaches vertical. It looks like the micropolygons are not dividing evenly along the edge, and the only remedy I can find is to increase the detail level above 1. Here are some examples with an unshaded surface. This is an image displacement.

I wonder if this is what Matt was referring to when he mentioned "extremely stretched vertical surfaces" in this thread. (The 3D preview of this example certainly looks extremely stretched.)

[Dune]

That is a problem indeed. I expect you used a compute normal after the first displacement of the canal? Did you try altering its patch size?
Another totally different solution I thought of, is using two long cubes for the sides of the canal, which would displace better. In the distance (and further from the canal to the sides) that can be merged into planet terrain.

[sboerner]

Yes, I tried various patch sizes over the course of working on this surface. There have been many permutations by now but I don't recall it making any difference. May try tweaking that again. (It's now set at 10.)

The cube idea is interesting, thanks. The scene is only about 5 km deep so planet curvature may not matter much. Have to give that a try.

On the other hand, the artifacts seem to become less noticeable as more layers of detail are added.

[j meyer]

What 'detail level' (MPD in the image) are you referring to, the detail in the render tab,
or the ray detail multiplier inside the render node?
If it's the first one you could try to increase the ray detail multiplier instead.

[Dune]

I don't think it would be the RDM, that's more for glass and transparency. Perhaps displacement tolerance in planet...

[j meyer]

For the latest VD stuff I posted I had to crank the RDM up to 0.75 to cure some
black spots, that wouldn't go otherwise. That made me think it might help here
as well.

[sboerner]

What 'detail level' (MPD in the image) are you referring to, the detail in the render tab

That's the one, Micropoly detail in the Quality tab. I'll investigate the RDM setting, can't hurt (though I thought that had more to do with secondary rays in transparency and reflection).


Ulco, I did wonder about displacement tolerance, too, but haven't tried that yet.

Here's a page from the wiki I hadn't seen before, might apply here.

[WAS]

Ray Detail Multiplier in Subdiv settings does indeed remedy this, at the cost of render times. Though I wonder if increasing MPD would be faster. I've noticed that for years with any soft displacement (where things need to remain soft). Especially doing sand ripples. It gets really bad with lateral surface detail and "noises" things up. It plagues Freeware version and makes every render garbage without upping Ray Detail Multiplier, which coupled with a 0.6 MPD cut-off, doesn't solve the problem entirely.

[sboerner]

Ray Detail Multiplier in Subdiv settings does indeed remedy this, at the cost of render times. Though I wonder if increasing MPD would be faster.

That would be simple enough to test. Something to look at.


For the record I increased displacement tolerance from 1 to 2 and it made no difference.

[WAS]

For the record I increased displacement tolerance from 1 to 2 and it made no difference.

Yeahh... this has never helped me in any instance. Tears, holes, and this scenario.