Extrusion/Subtraction functions of 3D Polys

[James Russell]

Hi all,

See the file attached.

I'm attempting to use a 3D polygon I've been provided with and I wish to create a solid from it that reaches my ground plane neatly but has the z-data attached to the upper vertices still. In the file attached imagine the 3D poly is the top of this solid and neatly meets the ground plane as the extrude does.

I've tried to subtract my poly from a solid trace, extrude the 3D poly itself, loft using it as a nurbs curve and several other things.

Any ideas? If you have queries let me know, I'm racking my brain!

J

[Gytis]

If you would please export to 2010, I'll try to take a look.

[bcd]

The 3d polygon looks like it should be redrawn smoother.

Then you could try:

Modify>Create Surface from curves.

Clean up the surface

Shell

Subtract solids

[James Russell]

Heya,

Attached is a 2010 version of the file.

Does it have to be redrawn smoother? I've been told it's an exact trace and would prefer to keep it that way...

I'll have a go at your suggestion though if I get a chance this afternoon.

Cheers,

J

[Kevin McAllister]

James,

I've played around a little with your file. There are some challenges with what you're trying to do. I played with the NURBS method and I don't think its possible because the top surface can't be generated. I can easily generate the sides and the bottom. I've attached a version with a triangulated top. Given that it started as polygons I'm guessing the top would need to be a triangulated surface instead of a NURBS surface. The top matches your 3D poly except at the point at the top when looking at it in plan view. There were two points directly on top of each other that caused problems. The top wasn't actually generated in VW but rather in C4D since its more suited to working with 3D polygons.

Can you tell us what the 3D polygon represents? That might help us give you some alternate solutions.

Kevin

[michaelk]

James

I think I got it to work. It's perfect candidate for the project tool in the 3rd mode. But, I'm sure you discovered, the 3D Poly won't work as a "target" for the tool.

The trick is to get the 3D poly to turn into something useful. Here's how I did it.

1. Start with the 3D polygon and the original polygon used to make the extrude.

2. Convert both to nurbs curves.

3. Select the top curve. Model > 3D Power Pack > Create Surface From Curves

This will give you a group of 1640 Nurbs Surfaces.

4. Edit the Group. Select All. Add Solids. (Wait........) Exit the Group. Ungroup. This gives you the same (I hope) surface as the 3D poly. At least it's very similar. Except for the inside of the elbow being filled in....

Go to an isometric view.

5. 3D Modeling Toolset > Project Tool > 3rd Mode (Add Mode)

Click on the bottom nurbs curve. Make sure the red arrow is pointed up - towards the solid addition. If not, use the second group in the mode bar to make it point the right direction.

Click on the solid addition.

Discard the solid addition.

hth

mk

[Gytis]

Michael-

That may well work for him, but there is some imprecision with that filled-in elbow of the NURBS surface. I've been trying hard (and failing) to create a surface within the bounds of the 3D polygon.

Though we are missing data as far as what happens within the boundary I'm surprised that VW is unable to generate something (short of painstakingly moving vertices in an Interpolated Surface).

[Kevin McAllister]

I did another experiment using the points of the 3D polygons as a starting point for a site model, since that tool is designed for finding surfaces from points. The site model will only generate something similar to what I posted, a facetted surface generated from triangulated faces.

Kevin

[bcd]

I still think the original 3d polygon needs to be redrawn using a nurbs curve, probably with fewer points - The task seems pretty doable then.

One thing I have learned from this exercise is the importance in naming your test file to include the word Challenge - it's a great hook

[James Russell]

Thanks for all your great replies guys, sorry I couldn't reply sooner (got stuck in China, boo!).

The background to this is that I'm currently drawing up a temporary venue to be located here in Melbourne for the Melbourne Festival in situ. Surveyors did their stuff, gave me a dxf with a whole heap of lovely contour lines which covered everything except for a rather large, obstructing, and inconvenient garden bed. When I asked for more detail about it I got this in my inbox, thus the challenge begins.

These solutions are great using advanced 3D poly techniques and using the Project Tool's 3rd Mode (probably for the first time ever personally) really pushes the high end of the knowledge base.

In the end it would have been much easier if I had the 20ish point NURB that I have no doubt this came from I'm glad that we all got to have a challenge together.

Till the next one,

J

[michaelk]

James

If you have the architect or landmark version of VW, and someone can put a survey into your inbox you could make a digital terrain model.

Then the fun really begins.

mk

[James Russell]

Michael,

I've been having fun for days...

See attached.

J