Opacity map -- bug on mattes

[davision]

This has probably been identified already.

But I'm seeing points where I have one piece of flat geometry on top of other geometry. If I turn everything to matte objects, AND the flat geometry has an opacity map on it -- the alpha disappears -- even though there is a solid matte object immediately underneath.

[vlado]

It is probably because you have objects with overlapping faces; in general it is best to try and avoid this - you can try to separate the objects by a tiny amount and see if it helps.

Best regards,
Vlado

[davision]

When you say 'overlapping' faces, do you mean literally coincident faces -- where they are at the 'exact' same place (z-coordinate in my case) ? Or do you simply mean some sort of intersection?

[vlado]

Yes, I meant coincident faces.

Best regards,
Vlado

[MoonDoggie]

I love all the names for coplanar/coincident/intesecting faces. Did I miss any?

[Dynedain]

I love all the names for coplanar/coincident/intesecting faces. Did I miss any?

Well, coincident is the correct term.

Technically, having coplanar items means a 2D plane can be drawn through them. Intersecting means that the two items pierce through each other. Coincident means that the two items share exist at the same location with the same 3D rotational orientation.

Overlapping is a non-technical term that makes more sense to people without an understanding of the geometry terminology.

Coincident faces by definition do intersect. But intersecting faces are not necessary coincident. Think two planes at 90 degrees to each other - they can intersect, but they'll never be coincident.

Coincident faces are also coplanar. But again, coplanar faces are not necessarily coincident. Think of two pieces of paper laying next to each other on a table. They are coplanar in that a single plane could be drawn through them connecting all their vertexes, but they are not coincident because they do not occupy the same location.


Clear as mud right?

[MoonDoggie]

An excellent explanation! I'll never use the wrong term again.

[ene.xis]

what term?

[RErender]

what term?

Glossiness?

[trixian]

Seriously, back on topic. This was a problem I had back on 1.5.r3 and maybe even earlier, and I definitely did not have any coincident faces.
The opacity map in the vray material cut away the matte object beneath it, so the transparent parts of the opacity map show as black (as far as I can remember), even though they should be shaded grey. You should send this file to Vlado if you can, unless you actually have coincident faces