Hey All,

Ok I have a geometry smoothing problem at the SOP level. When I knit the faces of PolyMesh together to close some surfaces off, I get a weird geometry problem only when I subdivide or render poly as subds. The problem is the surface tears apart at the seams the only place it stay connected are the orginal knit points or if I fuse a face to those points at those points. I also get sometimes part of the mesh seperating and cutting through the rest of the mesh in the area except for at the knit points. Is there a solution to this or am I going to have to subdivide to like level 3 and fuse every single point. That will take for ever and and would seem to be a large waste of time.

Cheers,
Nate Nesler

do you have any mid-edge points? (i.e. points lying along an edge with no other edges connected to them?)

that would cause some problems when subdividing…

The Facet Sop should solve your problem. Append a Facet SOP. I usually use these settings

Check “Make Normals unit length”
Select “Consolidate points fast”
Check “Remove Degenerate…”
Check “Post Compute Normals”

If you still get the problem, post a file or maybe some pics

Hey Michael,

I could not get it to work. Since I am so early on in the crowd sim I do not mind posting the actual file. Sorry I did not post earlier but I am continuing to have issues with the schools server. Tell me if you can even download the file. The server is on and off line alot so … I hope you can get the file.

http://janis.mtsu.edu/~nesler/Files/FlightCrowdSim/Ships_02.zip [janis.mtsu.edu]

Thanks For All Your Help,
Nate Nesler

You've got non-maifold polygons. What's going on is you have a bunch of edges that share more than two faces, that's bad. When you subdivide the mesh it splits the model open on those edges.

Looking at the TalzonOrganicAirShip OBJ, everything was going fine until you got to polyextrude29. You told the SOP to output a back on the extrusion and told it to output a back on every subsequent polyextrude. That created a bunch of interior faces and caused the problem. It seems like you can fix it though. I started going down the network turing output back off in the polyextrude options tab and it fixed the model without breaking it.

For future reference do not output a back on a polyextrude. I'm thinking very hard and honestly I can't come up with a situation where doing this won't generate an interior face and won't cause a problem save maybe if you did it on a closed curve. Even if you hadn't subdivide the model, you probably would have had trouble rendering it due to z sorting and normal issues.

Hey Michael,

Yeah I know I created “non-maifold” geometery but I need it there. Is it non-maifold instead of non-manifold I think I have been calling it the wrong thing? Other wise the compartments become open and you will be able to see straight through the ship when air is suppose to be passing through the wind tunnels. It effectively destroyes the illusion without them. Is there not a way around the surface spliting or do you have another suggestion for sealing off geometry in an organic way so that you can not look down into the ship through the wind tunnels? Would I have this problem in NURBS? I am very familar with NURBS in Maya but to be honest I have not really butted heads much with NURBS in Houdini. I don't like the refine SOP in Houdini for NURBS. I like the insert Isoparm in Maya much better but the pasted NURBS look quite interesting. Thank You For You Help.

Cheers,
Nate Nesler

OK, I see the problem here. You're going to need to change your modeling style a bit I think. You seem to be thinking of the object as shells rather than a solid volume. Considering an object as shells or patches works well if you are modeling with NURBS, not so well if you are using polygons. Something that'll help you out I think is to go into your viewport settings, in the culling tab, check “Remove back faces”. This will force you to think of your object as a closed volume because only faces with foward facing normals will be visible to you.

Now after looking at your file again there's a couple pointers I can give you that will help. First of all, polyextrude works on as many polygons as you care to select at the same time. I notice in your file you extrude a vent on one side and then the other. You can do both sides at once by selecting the faces on either side, and then using the scale handle.

Secondly. you are blasting faces to create the vents. A better approach would be to extrude the faces inward rather than blast the face away.

Here's a file that shows what I'm talking about. Just step through the SOP network. All the polyextrudes use the default setting except polyextrude6 for with I disabled “Output Front”

http://s91408461.onlinehome.us/polyextrude.hipnc [s91408461.onlinehome.us]

You might want to take alook at the modeling tutorial videos if you haven't already, especially the Val's shoe tutorial over at Vislab.