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Re: [Emc-developers] Inkscape, biarcs, and G-code!
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From: EBo <eb...@sa...> - 2009-02-02 07:59:31
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Hello Johnny, I'll have to poke around and see if my filter is still around and what shape it is in. It solved some problems for me then, but I have not looked at it much, if any, since... Either way, this functionality is probably available on the Inkscape side already. If not, you could write a little Inkscape module which uses their subdivision primitives and sort it out. If NURBS have been fully realized within EMC2, then that is the way to go. It would take me a little while remember and then to explain what transformations assumptions you need to make to go directly from a Bezier spline to a NURB, but off the top of my hear, all weights are set to 1, and the knot multiplicity is something like 3 on both ends and none any where else (not sure about that one though). Anyway, it would be a simple direct transformation with ***no*** linearization or "chordal deviation" but an exact solution. I found the paper "CAD/CAM INTEGRATION FOR NURBS PATH INTERPOLATION ON PC BASED REAL-TIME NUMERICAL CONTROL" via a google search, so I know it is out there, but I am unable to reproduce the search string. It was one of those fortuitous finger trips... Ah there it is <http://158.110.28.100/amst08/papers/art837759.pdf> and the following paper by Proctor et al. should also be helpful <http://www.isd.mel.nist.gov/documents/proctor/315openarchit.pdf> >From the examples shown in Loto at al.'s paper, it looks like there is a fully working NURBS implementation. What I remember from EMCv1 was only stubs if that. I will note however that there is no NURBS code in the emc2-trunk though. Can any one else comment? EBo -- Johnny Stenback <em...@js...> said: > Hello EBo, > > EBo wrote: > > Jst, > > > > That is so cool. I have some pointer on how to solve a couple of problems you > > either have stumbled against or will soon enough. Also, I missed Jeff Epler's > > posts on biarcs, etc., otherwise I would have jumped in earlier. > > > > First regarding hard coded linearizations, one of the best ways to linearize a > > spline is to subdivide the spline. Since Jeff's implementation appears to be > > based on quadratic Bezier splines, we can use the property that all spines are > > guaranteed to fit with the bounding box of the control polygon. You can > > simply fit a line between the two end points and calculate the Euclidean > > distance from the other two control points to determine what the maximum > > divergence from that line is. From there you can choose some arbitrary > > epsilon, check to see if the current spline falls out side that and subdivide > > the spline if the inner control points fall outside this epsilon. That will > > allow you to generate as many approximation lines to follow the Bezier spline > > as you need to stay within your chosen epsilon. You can do better than this > > however by then taking the number of linear segments and resubdivide trying to > > balance out the positions of the break points so you do not have a relatively > > short segment always at the end (this improves visual quality). This is all > > callable from within Inkscape. Back in 2004 I had a filter program which > > would take the spline output from Inkscape, then linearize it into standard > > g-code for a 2.5D engraver using this technique. > > Yes, I had ran into some of the issues with lineraization, or arcs not > really representing the curve very well, but so far this project is > early on enough that I hadn't spent much time figuring out how to > actually tackle that problem other than by bumping up the number of > biarcs it creates. But thanks for the pointers! Is your filter program > from back in those days available anywhere? > > > I was just about to make a comment on how Jeff's work could be used as a basis > > for implementing spline contours, but a quick search came up with a paper > > "CAD/CAM INTEGRATION FOR NURBS PATH INTERPOLATION ON PC BASED REAL-TIME > > NUMERICAL CONTROL" by Leto, Licari1, Lo Valvo1, and Piacentini1. Which > > demonstrates NURBS working within EMC2. HURRAAAYYY! Did you know that it is > > a relatively trivial issue to get helical interpolation (read point threading > > in in both milling machines and lathes), and lots of other things besides... > > That does sound exciting! Do you know if that paper is publicly > available anywhere? A quick google search didn't come up with anything > here... > > > Actually, assuming that the NURBS code has been integrated back into EMC2, > > then you should be able to write a Bezier to NURBS converter and be able to > > read any PDF or PS image directly into the NURBS -- since Bezier splines is a > > subclass of B-splines. So, I think this is doable directly in EMC > > ***provided*** NURBS have been integrated into the core. > > > > This, for me at least, is WAY EXCITING NEWS!!!!! > > Indeed! Does anyone know what the status of NURBS is EMC2 is? > > > > > EBo -- > > > > > > > > Johnny Stenback<em...@js...> said: > > > >> Hello all, > >> > >> I just wanted to share one of my recent late-night hacking outcomes. I > >> recently started looking into G-code generation of various kinds, and I > >> stumbled across Inkscape and Jeff Epler's gcode extension, and his work > >> on biarcs. I started playing around and eventually got the extension to > >> work in the latest version of Inkscape (0.46). I then made gcode produce > >> arcs (from circular arcs in Inkscape), and later on got Jeff's biarc.py > >> incorporated, so now the extension exports curves as biarcs (hard coded > >> to 5 per curve segment atm)! > >> > >> The code is by no means complete, and I'm fairly new to Python, so > >> there's probably some retarded stuff in there. The Z-axis movement isn't > >> always quite right (I might have broke that, but that's a detail that'll > >> work itself out over time here), but I wanted to share the fact that > >> generating G-code arc commands from biarcs, generated from curves in > >> inkscape works! > >> > >> The code is available to play with here: > >> > >> http://dp.jstenback.com/gcode/ > >> > >> I'd be interested to hear if anyone has thoughts or suggestions on this. > >> And a huge thanks to Jeff for his initial extension, and biarc.py! > >> > >> (this was sent to the emc-users list as well, but I figured maybe > >> there's people here who'd have thoughts too) > >> > >> -- > >> jst > >> > >> ------------------------------------------------------------------------------ > >> This SF.net email is sponsored by: > >> SourcForge Community > >> SourceForge wants to tell your story. > >> http://p.sf.net/sfu/sf-spreadtheword > >> _______________________________________________ > >> Emc-developers mailing list > >> Emc...@li... > >> https://lists.sourceforge.net/lists/listinfo/emc-developers > >> > > > > > > > > -- > jst > > ------------------------------------------------------------------------------ > This SF.net email is sponsored by: > SourcForge Community > SourceForge wants to tell your story. > http://p.sf.net/sfu/sf-spreadtheword > _______________________________________________ > Emc-developers mailing list > Emc...@li... > https://lists.sourceforge.net/lists/listinfo/emc-developers > -- |
