Regarding script interface for Curve and CurveSegment objects:

To clarify my understanding of the crv.evaluateTangent, and crv.evaluateDerivatives:

'FromLeft = true,' calculates tangents or derivatives, at points associated with NURBS parameter "t," with a "direction along the curve," starting from the domainMin towards the domainMax.
domainMin is associated with the start point of the curve.
domainMax is associated with the end point of the curve.

The values of the tangent or derivative is given as (x,y,z), a vector.
Sometimes the tangent vector values appear different from the 1st derivative values, but I think that the two vectors are parallel?

FromLeft = false, reverses the "direction" of calculation of tangent or derivatives. (INCOMPLETE STATEMENT, Only at discontinuity, see Michaels response.)

(Flipping the curve would result in reversing of FromLeft true vs false vector results. (except maybe at a corner point?))

For a straight line, all of the 'FromLeft = true tangents' for all of the points on the line, will be the same, as will all of the 1st derivatives.

In order to make a "Clothoid Blend" from a start point of a curve, the tangent at the startpoint will (MAYBE) have to be the "FromLeft = false" version. (FALSE)

A curve with a "corner point" in it, with non-tangent curve segments joined at the corner point, would have a discontinuity at the corner point. (This is like saying if it is not straight, it is crooked, a tautology :-)
The parametric "direction" across the join at the corner point is one way.

I think that the Blend command would benefit from incorporating "crv.isClickSelectedNearEnd" ?


For non-corner point tangents of a curve, the 'FromLeft = true' tangent is 180 degrees from the 'FromLeft = false' tangent. (FALSE)
At a corner point with the discontinuity, the 'FromLeft = true' tangent will not be 180 degrees from the 'FromLeft = false' tangent. (Otherwise the corner point is not at a discontinuity?)

- Brian

A CurveSegment is part of a curve consisting of joined segments.
Selecting a curve selects all of its segments.
Is there a corner point between all joined curve segments?
To tell if a curve has curve segments, Separate the curve. Is there another way?