xyzdist VEX function
>Finds the distance from a point to the closest location on surface geometry.

primid uvw VEX
Distance from Geometry SOPDistance from Geometry SOP

int prim;
vector uvw;
float distance = xyzdist(1, @P, prim, uvw);
vector hitpos = primuv(1, "P", prim, uvw);

3, 4
Primitive Id UV primuv VEX function 使