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# skEllipticalArc between two points

arthur_peters
Member Posts:

**19**✭Is there a way to have skEllipticalArc run between two points on the ellipse?

I already have the ellipse "description" (center, major, minor, axis) and the points that are on the ellipse (they are actually how the ellipse description is computed). However, I have not been able to figure out how to compute the start and end parameters for the points. I suspect the parameters is represented a fraction of the perimeter, but ellipse perimeter are terrible and I thought I would ask here before having to do numerical integration in FeatureScript. ;-)

PS: I'm doing ellipse fitting to points and tangents. I'm doing it directly since lofted surfaces seem to behave poorly when the provides use splines. I was unable to reliably use shell or thicken tools, even outward which should always be possible. Using approximations with circular arcs works better and I'm hoping ellipses will also work well and match my original shape better (an airfoil).

- Arthur (he/him)

0

## Comments

65PROTry this. I havent tested it but it might work, it should work. the only thing i am not sure of is if the ellipse wants arcLengthParameterization to true or false or if it doesn't matter.

19✭1,221✭✭✭✭✭1,120R * cos(t * 2 * PI)

r * sin(t * 2 * PI)

As t runs from 0 to 1 for a full ellipse. So no need for numerical integration; scaling, followed by atan2 is the thing to use here. It should also be significantly faster than creating an extraneous sketch (if you already had an ellipse, it'd be faster to use built-in projection methods, but creating a new sketch has non-trivial overhead).

19✭`arcLengthParameterization`

? Or does skEllipticalArc use the "non-arc length" parameterization by default?1,12019✭