Subject:
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LDraw part origin rule
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Newsgroups:
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lugnet.cad.dev
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Date:
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Wed, 25 Aug 2004 11:58:52 GMT
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Viewed:
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1780 times
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TrackDraw's parts are 2D models of 3D parts as viewed from the top. TrackDraw
attempts to maintain LDraw compatibility by using the same origin and
orientation. This allows TrackDraw to read and save layouts in *.ldr format.
For parts that exist, that's easy enough; I match TrackDraw's part to the LDraw
model. For parts that don't exist yet, it would be great if TrackDraw's 2D part
anticipates the origin and orientation of the LDraw part, whenever it gets
modeled.
I spoke briefly at BrickFest with Orion, and he confirmed that the rule is
basically the center of the studs, or if there are no studs, the center of the
'top' of the part. I'm not sure how to express this precisely, but I get it and
have oriented the TrackDraw parts to conform.
But some parts defy a simple orientation. One is the monorail half-curve. I've
recently determined that the geometry can be thought of as a 22.5 degree arc
with a center radius of 27.3509 studs (547.018 LDU); on the unnotched end,
there's an additional straight 0.6491 studs long (12.9822 LDU). The full curve
track pieces also have these straight sections on the ends; this allows the
middle of the quarter circle and the ends of the eighth circle pieces to be
stud-aligned.
So, how should I orient the half-curve? Should it be centered halfway along the
arc, or should it take the straight portion into account? Or should it get
oriented some other way? And in general, when parts are added to the part
tracker, is their origin and orientation part of the review process? Are there
formal rules for compliance?
Thanks
Cary
http://www.trackdraw.com
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