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# tangent of surface along U or V

adamohern
Member, OS Professional Posts:

**216**PRO
I can create a plane that is tangent to a surface at a given point.

1) How can I force the plane to align its X axis to the U or V direction of the surface at the intersection point?

2) How can I more generally extract the U or V tangent direction of a surface at a point?

1) How can I force the plane to align its X axis to the U or V direction of the surface at the intersection point?

2) How can I more generally extract the U or V tangent direction of a surface at a point?

0

## Comments

565I'm curious: What do you want UV directions for? In general, neither the end user nor the FS user has control over the internal parameterization of a given surface, so writing code that depends on the parameterization could behave differently than you or the end user expects.

216PRO2,003216PRO2,041PROSo I have a skPoint (a point in a sketch) and project this to the blue surface then create a plane. This is Lou's cool solution.

Things of interest:

-When querying a skPoint, world coordinates are returned. This is good because I don't have to transform it to know where it is in world space. The bad is that it doesn't know about how it was created ie.. what's the direction of the plane it was created on.

-The projection is a minimum distance from the point to the surface vs. a normal projection from sketch to surface.

If you are trying to create a 3D point on geometry using this technique, one would expect a normal projection based on the sketch view. The minimal distance isn't intuitive.

Using a sketch to create a 3D point on a surface will be off because evDistance returns minimal distance and not normal distance.

Gray line is the minimal distance and the orange line is the normal projection from sketch which is what I want.

Using a 2D sketch to generate a 3D point with a minimal distance projection isn't going to be intuitive and therefore not really a good way to create a 3D point on geometry. I'm trying to figure out how to generate a normal projection.

Is there an ev..... function that'll give you the intersection between a vector and a face?

Thanks for your help Lou,

472✭✭✭https://cad.onshape.com/documents/0de04acb5bac92ca16796edf/w/cdd1d1882311084fe54bff24/e/daaec91732ca5add243c90dd

See "Create tangent plane aligned with another vector"

216PRO