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## Re: [libredwg] Spline object?

 From: Jonathan Greig Subject: Re: [libredwg] Spline object? Date: Sat, 11 Dec 2010 01:50:26 -0600

Yes you can, a spline or bezier curve will be approximate but not perfect :)

Please see the attached files.  I have attached PNG screenshots of what the CAD files look like as well as several versions of DWG/DXF files. DWG_2000, DXF_2000, and DXF_R12 versions are provided.
The CAD Files contain several layers so that it is easy to identify the geometry the CAD file depicts.

A Spline is composed of several bezier curves. While bezier curves are somewhat complex, the math describing them isn't very hard at all if you can understand the geometry involved. The concepts involved include line intersection and tangent points and lines. The geometry behind a bezier curve must be understood or else the SPLINE will never be right. Here are 3 references to start with:

An absolute must for the mathematics involved. Riskus explains things very well. One of the best papers on beziers I've read:
http://itc.ktu.lt/itc354/Riskus354.pdf

Shows pictures of circle approximation with beziers to reinforce the concept:
http://en.wikipedia.org/wiki/B%C3%A9zier_spline

Shows animations of how a bezier curve works graphically and mathematically:
http://en.wikipedia.org/wiki/B%C3%A9zier_curve

On a side note, I would like to be much more involved in this project, but it is not LGPL licensed. The attached files are released to the public domain.

On Fri, Dec 10, 2010 at 12:51 PM, Ivan wrote:
Thank you.

Can you draw arc, or circle using single spline?

Bye

spline-circle.png
Description: PNG image

spline-circle-2000.dwg

spline-circle-2000.dxf
Description: application/dxf

spline-circle-R12.dxf
Description: application/dxf

spline-arc.png
Description: PNG image

spline-arc-2000.dwg