Does anyone have an idea what is causing this?   Background:  The sheet is a clothified hi-res square.  I used choreographed group to "pull it back" on the bed.  

The spikes do not appear on the preview panel.  I've tried rendering in P4, Firefly with and without raytracing and futzed with other settings, but always get the same result.  This is a firefly rendering using default settings.

Could this have something to do with lighting?

Thanks for any advise you can offer. 

My guess would be that this is because the simulator is folding polygons diagonally, resulting in highly non-planar polys; looking at the preview image, one can see several polys that have opposing vertices on the fold, rather than adjacent ones. I had the same problem with a very simple bedsheet simulation I tried to do.

Sorry I can't provide a solution to the problem, other than recommending an even higher resolution, which would entail exporting the high-res square and subdividing it in a modeling program, then re-importing it. I haven't used simulation until very recently, so I don't know what tricks there are to avoiding this without leaving Poser; I'm also looking forward to whatever answers you get.

Good luck!

What about the smooth ploygon setting or crease angle settings?? Maybe this will smooth it out.

I'm 99.9% sure its lack of Polys, Reason the spikes aren't showing till you render is probably the normals are looking the wrong way in the preview.....Looks good so far though......Steve

Alternatively it could just be your cloth room settings that need tinkering with to make it fold more smoothly instead of spikin like that.

Try reducing your Fold and Shear Resistance and see if that helps.

You'll probably want to turn on the "Cloth self-collision" option.

Thanks for the suggestions, everyone.

I've tried these things, and many others, but I'm coming to the conclusion that ptrope and Steve are correct.

I've downloaded Wings3D.  Now all I have to do is figure out how to use it.  Yikes.

Thanks again.

"My guess would be that this is because the simulator is folding polygons diagonally, resulting in highly non-planar polys; looking at the preview image, one can see several polys that have opposing vertices on the fold, rather than adjacent ones. I had the same problem with a very simple bedsheet simulation I tried to do."

That was my guess, too (but ptrope got in 1st). I get the same problem on some clothing, and usually fix it by exporting a .obj of the draped cloth and then using Hexagon to sort it out, either by smoothing it (usually) or by converting to triangles (which can sometimes work better). Smoothing sometimes shrinks the cloth in areas where it shouldn't get shrunk..

I have, but don't use or know Wings, but IIRC it has both these facilities. Try asking in the Wings forum here - they LOVE to help:-)

If you want to send the sheet to me I can try sorting it for you. IM me and we can arrange what to do. I usually visit at least once a day.

Cheers,
Diolma

Attached Link: Hi-res Square - Tripled

If you want to try it out, I've increased the resolution of the square by subdividing it, but more importantly, I've converted it entirely to 3- rather than 4-sided polys; hopefully, this will greatly reduce the occurence (it won't do so completely - there's always a possibility that the simulation will fold perpendicular to the edge of a poly) of "spikys."

Diolma:
Thanks.  I spent a few hours last night poking around Wings and figured out how to split the rectangle polys into triangles.  I tried converting some of my existing dynamic cloth items and ran a few test simulations.  I have to say that just this step has really increased the flexibility of dynamic cloth.  Haven't tried converting the sheet yet, but I'm optimistic!

ptrope:
Thanks very much for the improved hi-res square.  I will try the simulation tonight  and post the results.

David

Just wanted to post the latest simulation using ptrope's vastly improved hi-res-square.  What a difference!

I still have work to do--mostly because the new sheet is so flexible, I have to play with the choreographed group to tone it down a bit.  But at least it doesn't look like someone has a cactus under the sheets anymore!

High praise to ptrope.  I can't thank you enough for your help.

And thanks to everyone!

David

Glad you got it sorted LBT:-)

"I have to play with the choreographed group to tone it down a bit."

I'd be very interested if you could post an explanation of how you used the choreographed group on the mesh. I've never used it ('cos I don't really understand how to).

For doing something like you've done, I would first put something on the bed (probably a lo-res figure) and drop the cloth onto that. Then export the resulting cloth as a .obj, clear the simulation, delete the figure (or figures) import the saved cloth and do another simulation...

Cheers,
Diolma

Attached Link: http://www.e-frontier.com/article/articleview/1420/1/321/

Diolma:

I only just started using choreographed groups myself.  This link takes you to a tut that very straightforwardly describes how to use them.

Good Luck