Polylines made of arcs: determing bulge direction
Hello there,
I'm currently working on an interface to read out information from .dwg files using BricsCAD, Lisp and a program written in Delphi.
Reading the information I need with Lisp works just fine right now, but i stumbled over a problem, that turned out to be pretty essential on the Delphi side.
Polylines
can consist of ether lines or arcs or both. I see, that the bulge value determines, which direction the arc goes, but what I'm wrecking my brain over is, how does BricsCAD determine, which direction the bulge should go?
I should say, I'm not actually a cad uer, so I don't understand too much of it yet. Also I'm actually German, so please try to ignore the spelling and grammar misstakes and try to explain rather complex content as simple as possible.
Thank you.
Comments
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The direction of an LWPolyine arc segment is determined by the sign of the bulge: a positive bulge results in an anti-clockwise arc, a negative bulge results in a clockwise arc.
The bulge value represents the ratio of twice the length of the arc sagitta to the chord length of the arc, equivalently, the tangent of a quarter of the included angle of the arc; hence, in conjunction with the surrounding LWPolyline vertices, you have three arc parameters from which you can determine the center, radius, & included angle.
You may find my Bulge Conversion Functions of some assistance in this respect.0 -
Hi don't know , but this may be of interrest to you.
https://forum.bricsys.com/discussion/20429
Steven maybe you can explain to me the use for this. /Patrik
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