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 CAD / LDraw Files / Parts / 5655
5654  |  5656
Subject: 
Re: Conditional lines on sloped wedge parts 43720 and 43721
Newsgroups: 
lugnet.cad.dat.parts
Date: 
Mon, 18 Apr 2005 21:50:59 GMT
Viewed: 
4352 times
  
In lugnet.cad.dat.parts, Don Heyse wrote:
   In lugnet.cad.dat.parts, Steve Bliss wrote:
   In lugnet.cad.dat.parts, Niels Karsdorp wrote:
   Wedge part 45407 (Wedge 4 x 4 with 1 x 4 Side Plates) has similar sloped sides as wedge parts 43720 and 43721 . When I examined these parts in LDView, I noticed that the control points for the conditional lines on the sloped surface might be wrong:


I don’t think it’s the control points. I took a quick look at the file, actually just one of the lines, the first in the file. The control points used are the two unattached vertices from the triangles adjacent to the conditional edge. That should be exactly right.

It might be more the way the sloped surface is designed. These two images show how the conditional lines are sometimes “half-needed”:



I suspect that LDraw cannot outline this surface exactly correctly -- but I haven’t thought it through yet; I could be wrong.

A finer-grained surface, with more polygons, would work better. But would still have the problem of ‘half-needed’ conditional lines.

I’m not sure about that. The surface as it’s written is extremely lumpy, and the conditional lines work as expected given the lumps in the surface. You also get an ugly shading effect with flat shading because of those lumps.



There’s gotta be a way to cut the polys through the middle of the saddle and eliminate the problem. It looks like it might involve a ring (or torus) primative?

Well, I thought about this, and what I would try is changing the polygons thus:

If the top points are A1-5 and the bottom points are B1-5, keep the A2-B1, A3-B2 as currently, but instead of A2-B2 etc, use A3-B1, A4-B2, etc. I think that would make all the edges inside curves instead of outside, and eliminate the need for conditionals. But I’m not sure. And I dunno if it would “look right”.

ROSCO



Message has 1 Reply:
  Re: Conditional lines on sloped wedge parts 43720 and 43721
 
(...) OK, I tried it and realise now that it doesn't solve the problem at all, just moves the outside curves to a different spot. I think Don is right, a more complex torus-like curve is necessary to represent it properly. ROSCO (19 years ago, 18-Apr-05, to lugnet.cad.dat.parts, FTX)

Message is in Reply To:
  Re: Conditional lines on sloped wedge parts 43720 and 43721
 
(...) I'm not sure about that. The surface as it's written is extremely lumpy, and the conditional lines work as expected given the lumps in the surface. You also get an ugly shading effect with flat shading because of those lumps. (URL) There's (...) (19 years ago, 18-Apr-05, to lugnet.cad.dat.parts, FTX)

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