Displacement map

[Marc Chaumier]

Hi, I was trying to make a nice grass material, with displacement map, and what I get is that picture, not exactly what I expected... I try a lot of different bitmap file, but nothing work. Did someone know what's happening, or a discussion that talk about this issue? I meet often that sort of disagrement with displacement map. I give the material and the picture for study. Thanks.

[Roy Hirshkowitz]

There's something buggish about this image that I do need to check (for example, I'm not sure why it's getting stretched in one dimension)-- however, what you've got going is never going to work anyway--

You've got a 256 x 256 pixel image stretched to 196 inches (5 meters).  When I scale the thing more appropriately  I get the results below-- still not very good.  I don't think the map is very good for displacement grass.  It needs higher contrast and better tile boundaries.  There are some other user created displacement map materials for grass around-- it's not the easiest thing to do.

[Marc Chaumier]

Hi, Roy. I've sending an example very light of many images I've tried. Some of them was about 2000x2000 pixels, and, for displacement map, images with only black, grey & white points. I alaways get these distortions and the limits of the faces which compose the solid or complex faces are regrettably visible. I get these distortion, with other maps, like stone (even with high res. images as textures).

[Roy Hirshkowitz]

This is a different problem (I think).  It's one we've seen before.  I haven't really looked into it in depth-- it may not be easy to fix given the way AutoCAD tesselates things.  I'll have a chance to take a look next week sometime.

[Marc Chaumier]

Thanks a lot, it became a crucial tool to increase the quality of realistic images production (close plan).

[George Ioannidis]

Maybe you could try to model the wall differently? See attached. Just a thought and of course - additional work = pain in the ...

[Marc Chaumier]

Hi, george! Un chaleureux salut de la France à la Grèce. Thanks for your advice. I believe that I tried everything: 1 solid,solids, solid exploded, 3D faces, regions, polylines with thickness... Nothing works. Not the same distortions, but always distortions, always the problem of faces visibility, or lines. And many of these solutions spoil the productivity. My last chance is Roy ;o)

[Ros. Riha]

did you try all these variables such as VIEWRES, FACETRES etc.? I remember us having the same problem long time ago and it somewhow went off by itself - the only thing I can think of changing are these variables

[Roy Hirshkowitz]

Nope-- it's a real problem.  I'll get to it this week.  George's solution definitely won't work-- displacements require meshes-- distinct 3dfaces will have shading artifacts.

[George Ioannidis]

Good to know!

[Roy Hirshkowitz]

Here's where I am on this.

 

I fixed one obvious problem which occurs when the ray originates from inside the height field (displacement map.)  This was causing incorrect self-shadowing and indirect lighting within the displacement itself.  It was causing the edges of mesh faces to be visible.

 

However, the problem which remains is a significant one.  It stems from the fact that AutoCAD tesselations often produce long skinny triangles.  These "poor aspect ratio" triangles cause the current algorithm to work poorly.  I'm investigating a new algorithm for planar surfaces which should get rid of this problem with respect to most building facades, etc..  It will take a day or two to implement, but looks promising. 

 

Curved objects will resort to the old algorithm-- which means poor tesselations will continue to be poor.  You'll likely need a tool such as Rhino to produce better meshes for these.

[Marc Chaumier]

Thanks Roy for your work. If autocad use big triangles, is it to reduce the weight of the model? Your advice is to do all the model in rhino, yes? Not to do the curved surfaces in Rhino and import them in autocad? The problem would be the same? What is the best modeler for you (nxt)? And sketchup? Do autocad increase the quality of is way to deal with the faces along the uncountable release? It's true that Rhino is somewhere an "autocad-like"...

[Peter Milner]

AutoCAD 2011 does meshes and nurbs surfaces. Would these work for diplacement textures?