 | | Conditional lines on sloped wedge parts 43720 and 43721
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Wedge part 45407 (Wedge 4 x 4 with 1 x 4 Side Plates) has similar sloped sides as wedge parts 43720 and 43721 [LDrawPart 43721]. When I examined these parts in LDView, I noticed that the control points for the conditional lines on the sloped surface (...) (20 years ago, 16-Apr-05, to lugnet.cad.dat.parts, FTX)
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| | Re: Conditional lines on sloped wedge parts 43720 and 43721
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(...) 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 (...) (20 years ago, 18-Apr-05, to lugnet.cad.dat.parts, FTX)
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| | Re: Conditional lines on sloped wedge parts 43720 and 43721
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(...) 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 (...) (20 years ago, 18-Apr-05, to lugnet.cad.dat.parts, FTX)
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| | Re: Conditional lines on sloped wedge parts 43720 and 43721
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(...) 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 (...) (20 years ago, 18-Apr-05, to lugnet.cad.dat.parts, FTX)
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| | Re: Conditional lines on sloped wedge parts 43720 and 43721
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(...) 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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| | Re: Conditional lines on sloped wedge parts 43720 and 43721
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(...) 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 (...) (20 years ago, 19-Apr-05, to lugnet.cad.dat.parts, FTX)
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| | Re: Conditional lines on sloped wedge parts 43720 and 43721
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(...) 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)
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| | Re: Conditional lines on sloped wedge parts 43720 and 43721
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(...) I think the key difference is the twisted nature of this surface. I think the twist makes it impossible to partition the surface into polygons without having a mix of convex and concave seams. I'd like to be proven wrong. I don't have one of (...) (20 years ago, 19-Apr-05, to lugnet.cad.dat.parts, FTX)
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| | Re: Conditional lines on sloped wedge parts 43720 and 43721
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(...) 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)
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| | Re: Conditional lines on sloped wedge parts 43720 and 43721 [DAT]
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(...) Looks good. Should we create a new primitive with the next dimensions:? 2 24 0 0 1 0 1 1 2 24 1 0 -1 0 1 -1 2 24 0 0 1 1 0 -1 2 24 0 1 1 0 1 -1 and a POV-quadric version in the coming L3PPARTS. As the outer twisted surface of the parts with (...) (20 years ago, 25-Apr-05, to lugnet.cad.dat.parts)
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| | Re: Conditional lines on sloped wedge parts 43720 and 43721 [DAT]
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(...) Nice, I like the idea of the quadric primitive, but we want to add some curvature to the LDRAW version, right? I fiddled a bit with the part a few days ago, starting with the two triangles outlined by your primitive. I didn't exactly finish, (...) (20 years ago, 25-Apr-05, to lugnet.cad.dat.parts)
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| | Re: Conditional lines on sloped wedge parts 43720 and 43721 [DAT]
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(...) The following are the appropriate conditionals for Don's surface. Playing with it you can have angles where the conditionals seem to go too far, but it's certainly much better than the current ones. (Note that the last 4 conditionals are only (...) (20 years ago, 26-Apr-05, to lugnet.cad.dat.parts)
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| | Re: Conditional lines on sloped wedge parts 43720 and 43721
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(...) Hey, thanks testing it out. You're right about the conditionals zig-zagging a bit. I still have the feeling that if the surface were pinned down to the concave green line those zig-zags would go away. But I couldn't decide whether to divvy it (...) (20 years ago, 26-Apr-05, to lugnet.cad.dat.parts)
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| | Re: Conditional lines on sloped wedge parts 43720 and 43721 [DAT]
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(...) Good idea with a twist primitive (twist.dat ?). Perhaps it would be simpler if it were only in one octant: 2 24 0 0 0 0 0 1 2 24 0 0 1 1 1 1 2 24 1 1 1 0 1 0 2 24 0 1 0 0 0 0 POV code would be: //x - yz = 0 quadric { <0,0,0>, <0,0,-1>, (...) (20 years ago, 27-Apr-05, to lugnet.cad.dat.parts)
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| | Re: Conditional lines on sloped wedge parts 43720 and 43721 [DAT]
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(...) Ok so it's been a few years, but I took another look at this. Did anybody ever make a twist primitive? It appears like all you need to do is something like this. Don 0 Wedge 4 x 2 Sloped Left 0 Name: 43721.dat 0 Author: Donald Sutter 0 (...) (14 years ago, 22-Sep-10, to lugnet.cad.dat.parts)
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| | Re: Conditional lines on sloped wedge parts 43720 and 43721 [DAT]
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(...) Very interesting! (URL) I am not so much comvinced by the improvement for flat shading. Looks like we trade triangular artefacts in one direction with artefacts in the other one. But it drastically improves the very ugly condlines artefacts! (...) (14 years ago, 22-Sep-10, to lugnet.cad.dat.parts, FTX)
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| | Re: Conditional lines on sloped wedge parts 43720 and 43721
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(...) Unfortunately it messes up unless you inlude FTX line breaks, or fixed code box characters (pipe). Unfortunately, both make it harder for people using email or newsreaders, so probably best to do it as you did, browsers can just click "View (...) (14 years ago, 22-Sep-10, to lugnet.cad.dat.parts, FTX)
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