View Full Version : building a clean mesh

12 December 2004, 10:55 AM
Hey. This is something I've never really bothered with before, but I have a couple questions about building "clean" meshes. I know of some of the rules for building models for subdivisions. In this case though, I'm not dealing with subdivisions, but I'm still curious as to what other general rules I should follow.
This is wires from an older version of a building I've taken far too long to finish for the minas tirith project. Right now, I'm just trying to clean everything up, hence the topic.

First off, I've been told to avoid having any faces on objects intersecting each other. In this case, it would deal with something I did on one of the roofs: ( (wireframe: ( )
To get that look on the roof, I split the top polygon several times, and did a series of extrusions. The blocks on the outside were extruded separately. So, there are intersecting faces where the sides of these extrusions meet. In cases like this, does it really matter that there are intersecting faces? Should I take the time to cut the intersecting faces out and form a solid mesh, or just not worry about it?
For that matter, I'm curious about the rule in general. Say you're building an environment for a game, where you have part of a building coming out from the side of a cliff. In cases like this, could you model the cliff side and the building separately, then move the building into place at the side of the cliff until all the edges meet to make it look like it's coming out of the cliff side, or would you want to carefully construct the cliff mesh around the building to prevent any intersections? (Best example I could think of...)

Next question is more aimed at this image: (
I got those dozens of pieces of geometry in the rings going around the building by dividing polygons several times, and then building from there. What I'm left with though in one part of the image (left side shows it best) is a 28-sided polygon (taking all of its vertices into consideration). I imagine that in some cases, the triangulation on a polygon like that might look bad in a real-time renderer when the lighting comes in (they're using some sort of realtime renderer to demo the minas tirith project...). Should I divide polygons like that up? And if so, how much should I divide them?

01 January 2005, 02:28 AM
I don't know the answer.

I have been modeling similar things for a maya / renderman pipeline. Renderman is very fussy so I have been avoiding n-sided polys, non planar faces, multiple vertices/edges and conforming normals.

I guess it depends on why you are modelling it. In your second example: If it's for a game would you be better off keep the small repeated elements as seperate objects so that the main building can have fewer polys, and then the repeated boxey things can have their back face deleted? If it is for a rendered sequence then it depends on the renderer. If there are no render glitches as seperate objects then you could do that, or you could integrate them and divide up you 28 sided poly. I don't think 28 sided polys are ever a good idea.

01 January 2005, 08:24 PM
the answer to the first question is that it depends on the engine. The answer to the second quiestion.... in the case of a n-sided poly 1 of 2 things will happen in most real time engines... a) it won't work at all. b) it will triangulate it for you and thus cost you performance. If it doesn't look good when it's triangulated, you may have to think about another approach to modeling it. Also, i know that the minas tirith engine is a bit unique, so you should probably talk to the programmer for this question too. although, i doubt a 28 sided poly is gonna fly.

01 January 2005, 12:22 PM
vaguenic - That's a good idea, using separate pieces for those little parts. I never really considered it, because the last few times that I matched the geometry of objects up closely like that in a realtime renderer, the engine would still occaisonally render a gap in between the objects. But I may give that a try if the current model doesn't work.

The model is pre-triangulated though, since I sent the model in 3DS format. I guess the triangulation doesn't look TOO terrible...I'm going to wait to see how it runs in the viewer.

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