vray displacement "tearing" at uv seams

[ihavenofish]

hey there

i'm having a little problem getting zbrush displacement working in vray.. and every other renderer.

when using 2d mode the displacement is splitting the mesh on all the uv seams. using 3d mode with keep continuity gives no tears, but has normal errors so its not usable

i get the same tears in other renderers so i know its not a vray bug, but i cant seem to figure out what setting to change to fix it. does it just not like the zbrush mapping? any idea would be appreciated

thanks
later

[natty]

have you tried Tight Bounds ? that might solve your problem

[ihavenofish]

just tried that, a whole chunk of my mesh disappeared!
and it seems 3d mode with continuity on is in fact getting seam tearing too.

i have seen good renders out there (as i said, this is not limited to vray)
i am totally confused now.

later

[Long John]

try this:

first set your blur value of the displacement map from 1 to 0.
disabling filtering will not hurt either i think.

i think you know that you have to add a meshsmooth modifier to your mesh.

another point is that you have to know that you must flip the displacement map that zbrush exports.

ps:
as i see it 2d is the right way, 3d is for procedural textures not for UV mapped displacement.

[ihavenofish]

ok, well, i have tried just about everything and have gotton some really bizzare results... i'l post a bug thread in a few minutes.

but on the tearing, this is not smoothing related(or filtering, or flipping, i'm using a checker map for testing), the mesh is smooth, it even tears if its actually subdivided when mesh smothed. i'll upload the file for this in the bug section, even though its not really a bug because i cant upload here.

later

[cashgrow]

hey man, i had exactly the same problem and flipping the map is the solution, set the U tiling to -1 and the W angle to 180, solved the problem for me

[Long John]

mhm, i told him this before and it looks like this is not his problem.

[vlado]

At present, you will always get problems at uv seams, no matter what you do. As mentioned before, this is not limited to VRay. It is because at a uv seam the displacement function is discontinuous - it's value is undefined. Therefore a renderer must conjure up a different displacement function that the user will find more pleasing. The "Keep continuity" option in VRay tries to do that, sometimes successfully, at other times - not. Currently it only works across edges that have different material IDs.

One can certainly think of a way round the seams (I'm thinking about a solution at times, we'll see what happens), but my personal opinion is that texture maps are a bad choice for this particular job; not only because of the displacement problems, but also because it is very difficult to find good UV mapping for arbitrary models; plus a lot of the space in the bitmaps remains unused. There are a number of other ways to represent the necessary data in a far more usable way, without trying to squeeze 3d space onto a 2d bitmap.

Best regards,
Vlado