Hi, Chris!
> i have a few questions regarding working with ON_BezierCurves. I want to
> evaluate the tangents at the start and end points of a bezier curve. the
> function ON_BezierCurve::TangentAt() seems to be what i want, but it
> takes a double as its argument instead of a point. what does the double
> represent? distance from the beginning of the curve? how can i get the
> tangent at the beginning/end points of the curve?
The input double is the parameter, I think. A Bezier curve is a parametric
curve. The parameter t is usually between 0 to 1. So for the beginning point,
you can set t = 0, while for the end point, you can set t = 1. See:
http://en.wikipedia.org/wiki/B%C3%A9zier_curve
> also, is it possible to access specific control points of an
> ON_BezierCurve? I'm mostly concerned with the first and last points of
> the curve. the ON_BezierCurve::PointAt() looks close, but again, it
> takes a double as its argument and i'm not sure what to do with it.
The control points are accessible. Just use the double *CV(int cv_index) method
to return the control point, or use the GetCV method. The PointAt() method
returns the evaluating result of parameter t.
For the first and last control points of the curve, you can use CV(0) and
CV(xx.CVCount() - 1). For evaluation results, you can maybe use PointAt(0) and
PointAt(1).
Cheers!
Wu
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