[Closed] finding UV coordinates on mesh

not done it but my approach would probably be; find out which uvface the UV coordinate resides in, then compute the Barycentric coordinates for that point in that face… then use those coordinates to calculate the vertex position in the mesh face. If you look up “point in triangle” in google should get you all the info you need.

put “point in triangle” in google click on the first link scroll to the bottom twiddle your mouse in and out of the triangle.

Thanks for the link.
I tried to put that into a script but no success yet.
I don’t quite understand yet how this algorithm is supposed to work, but I’m getting closer…

(
	local meshObj = $Plane001
	local theChannel=1
	local UVsearch=[0.25,0.4]
	
		--collect all faces
	local meshFaces=meshObj.faces as bitarray
		--collect all verts for each face
	theMapFaces=for f in meshFaces collect meshop.getMapFace meshObj theChannel f
		--collect UV coords of each face/vertex
	theFaceVertsUVCoords=for v in theMapFaces collect
	(
		#(meshop.getMapVert meshObj theChannel v.x, meshop.getMapVert meshObj theChannel v.y, meshop.getMapVert meshObj theChannel v.z)
	)
		--Check if point is in triangle
	for f in theFaceVertsUVCoords do
	(
		A=f[1]
		B=f[2]
		C=f[3]
		u=UVsearch.x
		v=UVsearch.y
		P = A + u * (C - A) + v * (B - A)
			--Compute vectors   
		v0 = C - A
		v1 = B - A
		v2 = P - A
			--Compute dot products
		dot00 = dot v0 v0
		dot01 = dot v0 v1
		dot02 = dot v0 v2
		dot11 = dot v1 v1
		dot12 = dot v1 v2
			--Compute barycentric coordinate
		invDenom = 1.0 / (dot00 * dot11 - dot01 * dot01)
		u = (dot11 * dot02 - dot01 * dot12) * invDenom
		v = (dot00 * dot12 - dot01 * dot02) * invDenom

			--Check if point is in triangle
		result=(u > 0) and (v > 0) and (u + v < 1)
		format "A:% B:% C:% u:% v:% result:%
" A B C u v result
	)
)

output:

A:[0,0.25,0] B:[0,0,0] C:[0.25,0.25,0] u:0.25 v:0.4 result:true
A:[0.25,0,0] B:[0.25,0.25,0] C:[0,0,0] u:0.25 v:0.4 result:true
A:[0.25,0.25,0] B:[0.25,0,0] C:[0.5,0.25,0] u:0.25 v:0.4 result:true
A:[0.5,0,0] B:[0.5,0.25,0] C:[0.25,0,0] u:0.25 v:0.4 result:true
A:[0.5,0.25,0] B:[0.5,0,0] C:[0.75,0.25,0] u:0.25 v:0.4 result:true
A:[0.75,0,0] B:[0.75,0.25,0] C:[0.5,0,0] u:0.25 v:0.4 result:true
A:[0.75,0.25,0] B:[0.75,0,0] C:[1,0.25,0] u:0.25 v:0.4 result:true
A:[1,0,0] B:[1,0.25,0] C:[0.75,0,0] u:0.25 v:0.4 result:true
A:[0,0.5,0] B:[0,0.25,0] C:[0.25,0.5,0] u:0.25 v:0.4 result:true
A:[0.25,0.25,0] B:[0.25,0.5,0] C:[0,0.25,0] u:0.25 v:0.4 result:true
A:[0.25,0.5,0] B:[0.25,0.25,0] C:[0.5,0.5,0] u:0.25 v:0.4 result:true
A:[0.5,0.25,0] B:[0.5,0.5,0] C:[0.25,0.25,0] u:0.25 v:0.4 result:true
A:[0.5,0.5,0] B:[0.5,0.25,0] C:[0.75,0.5,0] u:0.25 v:0.4 result:true
A:[0.75,0.25,0] B:[0.75,0.5,0] C:[0.5,0.25,0] u:0.25 v:0.4 result:true
A:[0.75,0.5,0] B:[0.75,0.25,0] C:[1,0.5,0] u:0.25 v:0.4 result:true
A:[1,0.25,0] B:[1,0.5,0] C:[0.75,0.25,0] u:0.25 v:0.4 result:true
A:[0,0.75,0] B:[0,0.5,0] C:[0.25,0.75,0] u:0.25 v:0.4 result:true
A:[0.25,0.5,0] B:[0.25,0.75,0] C:[0,0.5,0] u:0.25 v:0.4 result:true
A:[0.25,0.75,0] B:[0.25,0.5,0] C:[0.5,0.75,0] u:0.25 v:0.4 result:true
A:[0.5,0.5,0] B:[0.5,0.75,0] C:[0.25,0.5,0] u:0.25 v:0.4 result:true
A:[0.5,0.75,0] B:[0.5,0.5,0] C:[0.75,0.75,0] u:0.25 v:0.4 result:true
A:[0.75,0.5,0] B:[0.75,0.75,0] C:[0.5,0.5,0] u:0.25 v:0.4 result:true
A:[0.75,0.75,0] B:[0.75,0.5,0] C:[1,0.75,0] u:0.25 v:0.4 result:true
A:[1,0.5,0] B:[1,0.75,0] C:[0.75,0.5,0] u:0.25 v:0.4 result:true
A:[0,1,0] B:[0,0.75,0] C:[0.25,1,0] u:0.25 v:0.4 result:true
A:[0.25,0.75,0] B:[0.25,1,0] C:[0,0.75,0] u:0.25 v:0.4 result:true
A:[0.25,1,0] B:[0.25,0.75,0] C:[0.5,1,0] u:0.25 v:0.4 result:true
A:[0.5,0.75,0] B:[0.5,1,0] C:[0.25,0.75,0] u:0.25 v:0.4 result:true
A:[0.5,1,0] B:[0.5,0.75,0] C:[0.75,1,0] u:0.25 v:0.4 result:true
A:[0.75,0.75,0] B:[0.75,1,0] C:[0.5,0.75,0] u:0.25 v:0.4 result:true
A:[0.75,1,0] B:[0.75,0.75,0] C:[1,1,0] u:0.25 v:0.4 result:true
A:[1,0.75,0] B:[1,1,0] C:[0.75,0.75,0] u:0.25 v:0.4 result:true

result:true for everything is wrong…

isn’t P just the UV coordinate ?

fn PointInTriangle A B C pnt &u &v &w =
 (
 	v0 = C - A
 	v1 = B - A
 	v2 = pnt - A
 
 -- Compute dot products
 	
 	dot00 = dot v0  v0;
 	dot01 = dot v0  v1;
 	dot02 = dot v0  v2;
 	dot11 = dot v1  v1;
 	dot12 = dot v1  v2;
 
 -- Compute barycentric coordinates
 	
 	invDenom = 1 / (dot00 * dot11 - dot01 * dot01)
 	u = (dot11 * dot02 - dot01 * dot12) * invDenom
 	v = (dot00 * dot12 - dot01 * dot02) * invDenom
 	w = 1 - (u + v);
 	
 --	 Check if point is in triangle
 	
 	(u > 0) and (v > 0) and (u + v < 1);
 )

still no luck, but now I used the “slower” method described on the site:

(
	local meshObj = $Plane001
	local theChannel=1
	local UVsearch=[0.02,0.019,0]
	
		--collect all faces
	local meshFaces=meshObj.faces as bitarray
		--collect all verts for each face
	theMapFaces=for f in meshFaces collect meshop.getMapFace meshObj theChannel f
		--collect UV coords of each face/vertex
	theFaceVertsUVCoords=for v in theMapFaces collect
	(
		#(meshop.getMapVert meshObj theChannel v.x, meshop.getMapVert meshObj theChannel v.y, meshop.getMapVert meshObj theChannel v.z)
	)


	function SameSide p1 p2 a b = dot (cross (b-a) (p1-a)) (cross (b-a) (p2-a))>=0
	function PointInTriangle p a b c = (SameSide p a b c) and (SameSide p b a c) and (SameSide p c a b)
		
		--collect all affected faces
	hitFaces=for f in theFaceVertsUVCoords collect PointInTriangle UVsearch f[1] f[2] f[3] --Check if point is in triangle	
	
	for f=1 to hitFaces.count where hitFaces[f]==true do
	(
		print f
	)
)

It works!
I can find all faces “touched” by a specific UV position.
But what I really need is to convert the UV position to barycentric coordinates of that face.
Sounds easy, but how?

EDIT: think I have figured out the whole thing…will post the solution later…

I think it isn’t much difficult, but take some hours to make that script.
From a 2D point in UV, you can find all UV faces containing that point.
Depend on their relative postion in that UV face you can calculate the real postion in 3D