Ellipsoids

[Cloud Hidden]

Trying to subtract an ellipsoid shape from another object. Using Ellipsoid Object tool. But it only cuts the "shell" of the ellipsoid from my base object, not the whole ellipsoid. Tried first making it a solid (won't happen) or nurbs surface, but neither make a diff. How to subtract a solid ellipsoid, rather than just the surface of the ellipsoid, from another solid?

I imagine I can sweep an ellipsoid and use that, but the ellipsoid object is a cleaner, smoother object that I've used for another part of the design, and I'd like to keep using it as an exact match of the other ellipsoid to subtract from other objects. I could also decompose the resulting subtracted object and delete the interior part I don't want, but that's extra work. It'd just be nice if I could subtract a solid ellipsoid, and I can't figure out where it's going awry.

Thanks.

[michaelk]

No one seems to be answering, so I'll dip my toe in first.

If you ungroup the ellipsoid object you will get a nurbs surface. But that doesn't help you.

Sweeping 1/2 an ellipse - split along the major axis - sounds like the best way. But I can't think of an easy way to draw a geometrically correct ellipse. There must be a way, but searching the manual for ellipse (and ellipsoid) returns nothing.

I tried to make an ellipse and ended up using the same method Euclid would have use if he had been a VW user. Draw a diagonal line - sweep the line to make a cone - switch to a front view of the cone - split the cone - extract the curve of the cut - now you have a nurbs curve ellipse.

Rotate it flat to the ground plane - convert to polygon.

Whew. Ellipse. (There has to be a better way)

Split the ellipse along the major axis. Sweep the result. Ellipsoid. This will subtract from another solid.

That convoluted method gets you a random, unknown ellipse and a random, unknown ellipsoid. But not a predetermined ellipse and ellipsoid.

You do get a little bit of "banding" along the surface at the subtraction. Maybe someone else will have a good solution for that.

Sorry, not very helpful...

michaelk

[Cloud Hidden]

It would seem that there should be a way to make a closed nurbs surface a solid rather than only a hollow shell, but I can't find such a way. The ellipsoid object responds nicely to the shell command and other things I try with it, but I can't get it to be solid....kinda like only being able to buy hollow easter bunnies instead of solid ones.

I have an idea to try next, although it'll be a pain. Create ellipsoid object. Create a shell to the exterior that's really thick. Create a rectangular object that encompasses the hollow core of the ellipsoid, but is encompassed by the shell, and then subtract the one from the other, leaving the core as a solid ellipsoid. We'll see if it works.

[Cloud Hidden]

Ha!!!!!!!! That worked! Wouldn't have thought of it if I hadn't mulled over your post, so thanks. It's certainly convoluted, but it works, so....

[michaelk]

For a long time I've wished for a way to "fill up the easter egg", ie. create a solid bounded by a nurbs (or mesh) surface.

Interesting trick. It still doesn't allow you to create an ellipsoid from an ellipse of a given set of loci... But it does give an ellipse whose outside dimension you can control. I suppose you could work the math backwards by scaling the ellipse or ellipsoid to get the final size.....

I never thought about the absence of conic sections (other than the circle) tools. There are no hyperbola or parabola tools either (that I know of).

Let us know how the shell trick works. Seems like it should produce a smoother solid than a sweep.

michaelk

[michaelk]

Is it smoother than a sweep?

michaelk

[Cloud Hidden]

Yes, it is smoother. Looks exactly like the ellipsoid object except it's solid.

It's a much more controllable object from which I should avoid facetted surfaces. I can work back to the loci. I set the ellipse by length and width, and since it's a building, that's what the builders and permit officers (and tax assessors) want. The loci are the easy part.

[Pat Stanford]

How about duplicating the Elipsoid in place and then selecting both parts and either Add Solids or Intersect Solids?

Where is the elipsoid tool? I can't find it in the program or the help files.

[michaelk]

Just tried it. Very cool...

And not as convoluted as Euclid might have done.

michaelk

[michaelk]

Pat

It's in the Solids Tool Set (didn't know there was such a thing). I couldn't find it in the manual but it was available in the workspace editor.

It creates a nurbs surface of an ellipsoid. Would adding or intersecting a nurbs surface create a solid?

michaelk

Edited May 19, 2009 by michaelk

[michaelk]

I can work back to the loci. I set the ellipse by length and width, and since it's a building, that's what the builders and permit officers (and tax assessors) want. The loci are the easy part.

It's a really cool solution. How did you know about the secret (not in the manual) solid tool set?

I assume you are trying to do something like align the loci of a hemisphere and the loci of an ellipsoid... Are you doing the math or does VW provide a snap point to the loci?

michaelk

[Cloud Hidden]

How did you know about the secret (not in the manual) solid tool set?

I assume you are trying to do something like align the loci of a hemisphere and the loci of an ellipsoid... Are you doing the math or does VW provide a snap point to the loci?

michaelk

Manual? What manual?

There used to be an ellipsis tool that I downloaded from some site (and torus, cone and others). I went snooping in the workspace tool set for it, didn't find that exact one, but did find this one. So it was half by accident and half by intention.

My mistake on the loci. You're talking about loci, but I was thinking about an ellipsis' "foci'...that's bad enough to cost me $$$ on Wheel of Fortune!

Don't need to do much more than work with the primary shapes...nothing to really align. The ellipsoid is the shape of a house, we create the shape of a special material, inflate it, spray it with polyurethane foam and concrete, and doll it up with gingerbread. Makes a cool house.

[michaelk]

No, you're right. It should be "foci".

I also stumbled across that tool set after you said you were using that tool.

Maybe it's a "legacy" tool set.

michaelk

[islandmon]

The ellipsoid is the shape of a house, we create the shape of a special material, inflate it, spray it with polyurethane foam and concrete, and doll it up with gingerbread. Makes a cool house.

Are you using ccSPF ( close-cell Spray Polyurethane Foam ) ?

[Keith W]

Do you use jellybeans and icing on your gingerbread?

Seriously, there are some great dome houses out there: are you the outfit (I thought it was in Texas) that does these? Ah, there it is, the Monolithic Dome Institute...

keith

[Cloud Hidden]

Yes, ccSPF.

And yes, those same houses, but I'm independent of them.