LEGO Elements/Parts : 5657


CAD / LDraw Files / Parts / 5657	5656 \| 5658

Subject:	Re: Conditional lines on sloped wedge parts 43720 and 43721
Newsgroups:	lugnet.cad.dat.parts
Date:	Tue, 19 Apr 2005 11:32:36 GMT
Viewed:	4753 times

In lugnet.cad.dat.parts, Ross Crawford wrote:

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”.

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.

I’m pretty sure that’s going to be the problem with *any* partition of this surface into polygons. Having a mathematical description of the surface would be good, because then we could potentially create a primitive for the surface, and rendering programs could substitute a smooth-curve construct for the primitive.

In the LDraw code, I believe the appropriate fix will be to replace the current coarse mesh with a mesh that’s fine enough so that the potential error (ie, the distance from the ideal brick surface to the LDraw conditional edge) is less than 1 pixel (at reasonable magnifications). I’m not sure how fine such a mesh will be, we might have to settle for coming within a couple of pixels...

Steve

Message has 2 Replies:

		Re: Conditional lines on sloped wedge parts 43720 and 43721
(...) Oh, I don't know about that 1 pixel business. The problem with the surface as it's currently written, is that it flip-flops between convex and concave every at every triangle. But if you ignore the triangles and spin the surface around a bit, (...) (20 years ago, 19-Apr-05, to lugnet.cad.dat.parts, FTX)

		Re: Conditional lines on sloped wedge parts 43720 and 43721
(...) I have made a 43720.inc for the test of the coming L3PPARTS. The mathematical description of the surface is: 80x + 40y + yz = 0 and I have used the POV primitive quadric: quadric { <0,0,0>, <0,0,1>, <80,40,0>, 0 clipped_by { box { <-20,0,-40>, (...) (20 years ago, 25-Apr-05, to lugnet.cad.dat.parts)

Message is in Reply To:

		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 (20 years ago, 18-Apr-05, to lugnet.cad.dat.parts, FTX)

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