I'm trying to use R to determine the quality of a cubic Bezier curve approximation of an elliptical arc. I know the four control points and I want to compute (x,y) coordinates of many points on the curve. I can't find anything in either the base distribution or CRAN that does this; all the spline-related packages seem to be about *fitting* piecewise Bezier curves to a data set. Presumably, internally they have the capability I need, but it doesn't seem to be exposed in a straightforward way. Help?
how to evaluate a cubic Bezier curve (B-spline?) given the four control points
2 messages · Zack Weinberg, Greg Snow
2 days later
You could look at the xspline function. It approximates b-splines or Bezier curves given control points and shape parameters. It can either plot the spline or return a bunch of point on the curve for comparison to other values. Hope this helps, -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare greg.snow at imail.org 801.408.8111
-----Original Message----- From: r-help-bounces at r-project.org [mailto:r-help-bounces at r- project.org] On Behalf Of Zack Weinberg Sent: Friday, October 10, 2008 4:11 PM To: r-help at r-project.org Subject: [R] how to evaluate a cubic Bezier curve (B-spline?) given the four control points I'm trying to use R to determine the quality of a cubic Bezier curve approximation of an elliptical arc. I know the four control points and I want to compute (x,y) coordinates of many points on the curve. I can't find anything in either the base distribution or CRAN that does this; all the spline-related packages seem to be about *fitting* piecewise Bezier curves to a data set. Presumably, internally they have the capability I need, but it doesn't seem to be exposed in a straightforward way. Help?
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