Another question:
How do I get the U coordinate of a point on a curve?

dinkleberry
Another question:
How do I get the U coordinate of a point on a curve?

Append UVTextureSOP to your curve, set Texture Type: Rows&Columns and Apply to: Point texture. Done. Points uvs follow implicit curve coordinate U.

cheers,
skk.

Sweet, thanks.

Depending on what you want, you can also use the primuv() expression to fetch any attribute value at the specific u and v position along the curve. If you query the “P” attribute you get the actual “u” position along the curve.

It is common to wrap primuv() with the pointdist() expression which will return you the closest spot on a primitive from a given point.

I've been looking for a vex version of pointdist, seems like the Primitive Attribute VOP does the same thing as the primuv expression but is there a vex equivalent of pointdist?

tjeeds
I've been looking for a vex version of pointdist, seems like the Primitive Attribute VOP does the same thing as the primuv expression but is there a vex equivalent of pointdist?

I'm afraid there is not. People are asking for this a lot. Looks like a good candidate for a RFE.

Here [forums.odforce.net] you have a discussion on similar issue.

Just for the record, there is another way…

Using an attribcreate sop, create a float point attribute, and set the following as the expression:

fit($PT, 0, $NPT-1, 0, 1)

G

keyframe
Just for the record, there is another way…

Using an attribcreate sop, create a float point attribute, and set the following as the expression:

fit($PT, 0, $NPT-1, 0, 1)

G

This assumes uniform parameterization and a 0-1 domain, which is not always the case with NURBS and Bezier curves. Also, I am not sure it handles closed curves well. The safest way to access the U coordinate is to use the primuv() expression, as Jeff suggested earlier.

I was trying to do something similar, but I can't get it to work. I want to find the closest point on a curve, but the primuv + pointdist solution does not seem to give the right point. I think it is due to the fact that the curve does not have a domain…

I have tried various things, but no luck…

See attached file

Hi All,
I'm using primuv() in VEX to get the “P” attrib on a curve at the specific UV location. Is there a way to find the opposite in VEX, given the point “P” attribute, return the UV location? Points not in a straight line, randomly positioned in space, unevenly distributed.

Thanks

Look at xyzdist(), It will return closest prim and uv.

Returns the distance to the closest point on the geometry. This will find positions on the surfaces of the geometry, not just point positions.