Creating a "Tarp" (Wrapping a closed datum curve)?

[bgalanti]

I'm basically trying to create a surface that looks like a tarp over the geometry. Basically to take a rectangular surface and "drape" it over geometry.

I've tried a number of different techniques, and using Wrap is the closest I've gotten, but it's still not quite right.  The reason I was using wrap was I wanted to keep the lengths of each edge of the tarp a fixed length, and then have them just end up wherever they go.

However,  when I try to do this, I can't seem to get the beginning and the end of the curve to match up. Creo seems to be trying to force the sides to be horizontal, when they shouldn't be.

I tried using a spline to as an experiment, so that I just had a single curve, but there was still the discontinuity at the beginning/end point. Is there any way to force the wrap to keep the closed shape of the original sketch? I've played some with the Center option and a sketched coordinate system in the wrap command, but I haven't quite figured out exactly how that works, and the help doesn't really explain it.

Does anyone have any suggestions? Is there some other method I should be trying?

Thanks!

[Patriot_1776]

The advantage of the Wrap is that it DOES keep the lengths the same.  BUT, I can already see an issue with what you're trying to do:  You're trying to wrap a curve on 2 separate areas where the geometry is different (that stepped area to the left) so right there you're going to have problems.  I'm surprised it worked at all, what was it supposed to do with that short vertical face?  You're trying to stretch the wrap there, and it SHOULD have failed.  HOWEVER, you should be able to trim the curve segments afterward.

[bgalanti]

I wasn't sure if wrap would stretch on vertical faces or not. I'll try putting a small draft on all the vertical faces and see if that helps. It's probably a bit more "realistic" anyway, since a tarp wouldn't conform to vertical surfaces.

[Patriot_1776]

From what I saw, you're asking the Wrap (tarp) to stretch, that MIGHT help.

[bgalanti]

Yeah, the whole thing I'm trying to get at is NO stretch of the edges. I tried adding a bit of draft along all the height changes, and rounds at all the edges so that there weren't any vertical surfaces or discontinuities, but that didn't help (see the attached picture).

[Patriot_1776]

Yeah, you're asking for more than the Wrap was designed to do.  You ARE asking it to stretch, only in certain areas.  You'll probably have to end up extending and trimming the curves to get what you want.

Good luck!

[John.Pryal]

'Flatten Quilt' maybe? I don't know if it would handle the corners but worth a try!

Good luck

John

[Patriot_1776]

'Morning John!  Yeah, good call, I forgot to suggest that.  Me, I've never actually had occasion to try it so I'm unfamiliar with it.  I've managed to do everything I've needed to do without it, never needed to do anything like this.  Worth a try for him perhaps! 

[bgalanti]

Flatten quilt is the path I started going down yesterday and it might be the right option. I was able to flatten a quilt, then trim up the flattened quilt to make it square. Then I used flatten-quilt deformation to drape the now square "tarp" back over the items. It worked pretty well, but I only did a small portion of my "cargo"

The trick now is to create a good quilt to flatten. I think I might try creating some curves down the length using cross sections, and then see if I can tweak them so it doesn't look quite so much like a vacuum pack. Then I can blend a surface between the curves and try flattening that.

We'll see how it goes...

[Patriot_1776]

Are you trying to design a specific size tarp for a particular cargo application?  Knowing what you're trying to do is always helpful.  Like me knowing what the duct work was for in another thread here.

[bgalanti]

Well, they are trying to see what kind of coverage various tarp sizes would give so they know what to order. So, I'm trying to give a rough visualization of what the various sizes would look like when strapped down for transport over the system.

[Patriot_1776]

Sounds like there's WAY easier ways to figure that out.  I'd say you could easily figure that out with 2 surfaces at 90deg to each other intersecting the objects representing the "packages", then do intersections (curve creation), and measure the length of the resultant curve.  As long as you have the coverage down the side that you want, it'd be fast and accurate enough for gov't work as they say.