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Message - Re: Sailing (very round) Ships

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Posted by  Jerud Crandall on March 01, 2001 at 09:43:55:

In Reply to:  Re: Sailing Ships posted by Bob Sprague on February 27, 2001 at 14:48:21:


made me jump out of my chair!

> that a geodesic dome has similar sized polygons rotating around a
> common vertical axis at the same spacing along same latitude?

Pretty much, yeah. It depends on the frequency of the dome, but for this dome (frequency-3), there is a pentagon whose center is the top-
center of the dome. Therefore, there is a set pattern of triangles
rotated five times (at 72degree intervals) around that central axis. shows this graphically.

> If this is true, can you not draw a plan view of each of these
> polygons in your CAD program, each incorporating the approporiate
> amount of detail and then... Import each type into DW and in
> elevation(section) raise one to the appropriate latitude of the
> dome, tilt it correctly and then circular duplicate it around the
> vertical center to?

Well, yes, in fact i can. If you goto the above page, you'll see that
there are in fact just two different triangles, arranged in hexagons and pentagons. What you described is basically the method i mentioned earlier when i referred to "tedious work". I would create the appropriate triangular slabs, and arrange them into hexs and pents. Since the triangles which make up the hexs and pents are not coplanar, i'd angle the first triangle, then duplicate it circular (5 or 6 times, depending) around the vertical axis of the hex/pent. Then i'd have my hex/pents all with the center vertex "pulled out" a little. From here, i'd make 1 pent and 3 hexs, orient each at the correct angle, butt them all up against one another. Then i'd place ad additional pent at the top and rotate the aforementioned assembly around the pent's center vertex. There would be some triangles to trim off of the bottom hexagons, and then i'd have my shell.

As you see, though, there is an unhappy amount of math involved in the above method. I'm perfectly capable of sitting down and figuring out all the compound angles that i'd need to. In some ways, DW can help with this because i can space-jump to the vertices and use the coordinates to do all the trig. But you can see why i don't look forward to that. I've been pursuing this for a few months now, so as you may have figured out, this is a personal project -- there is no customer waiting on this (good thing, too!). So i have the luxury of waiting around to see if a solution can be developed. Especially since it may benefit other users who develop related problems. Users who *do* have a customer waiting on them.

The fundamental issue here is that the 'arbitrary working orientation' tool doesn't work with the wireframes i've imported because they don't have the orientation info in them that dw objects would. This is perfectly understandable, but the dxf import feature is quite useful, and it would be best if the arbitrary tool could work with them -- both for me and others.

So in a nutshell, thanks for the suggestion and enthusiasm. I hope this works out for the sake of everybody, but if it doesn't i'll still keep the group informed. Will probably post my completed shell (whenever that happens) in the library.



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