Select vertex in UV map based on coordinate x,y

Question

I have a problem similar to my last one but yet I can't find an efficient solution.

Having an array of [x,y] coordinate that indicate position on the UV map I want to select the closest vertices ( in 3D )

I'm guessing the main idea would be to iterate upon my array of coordinate and then compute the distance to each vertices on the UV map with 2 for loop ( one for face in bm.faces, and another for loop in loop in face.loops ) but that would be not efficient.

What is my best option here ?

Any help is welcome.

thx.

Possible performance issues? I mean what is the size of the array and what is the size of the mesh? — lemon, Jul 25 '19 at 13:55
like I have 200 hundred coordinates on a 200k+ vertices mesh so that would make 40 millions distance to test. I feel like I could maybe use the operator bpy.ops.uv.select_circle() that would but I don't understand how to use it. — Edmond Boulet-Gilly, Jul 25 '19 at 14:00
Just an idea: handle the UV map as if it is a mesh (make a mesh from it), then build a bvh tree and ray cast on it. If you handle this pseudo mesh faces index correctly you should retrieve easily the corresponding face of the mesh in 3D. Reference https://docs.blender.org/api/current/mathutils.bvhtree.html#mathutils.bvhtree.BVHTree.ray_cast — lemon, Jul 25 '19 at 14:03
Close to what you need https://blender.stackexchange.com/questions/79236/access-color-of-a-point-given-the-3d-position-on-the-surface-of-a-polygon/79251#79251 and this also https://blender.stackexchange.com/questions/77607/how-to-get-the-3d-coordinates-of-the-visible-vertices-in-a-rendered-image-in-ble/77747#77747 (use ray cast) — lemon, Jul 25 '19 at 14:11

lemon · Accepted Answer · 2019-07-26T07:04:49.643

I propose to use a kdtree so that we'll have an efficient search tree over the UV Map, for all the coordinates you have in input.

The principle is the following:

Create a kdtree and populate it with UV coordinates
Initialize it
Search on it from the input coordinates you have
From this index, get the corresponding vertex index (in the 3D mesh) using the loops

The tree is initialized once per mesh and allows multiple searches.

The commented code:

import bpy
import bmesh
from mathutils import Vector
from mathutils.kdtree import KDTree


print( '-------------------------------' )

# Do all that in object mode
bpy.ops.object.mode_set(mode = 'OBJECT')

# Get the mesh
obj = bpy.context.active_object

# Get its UV map
uvmap = obj.data.uv_layers['UVMap']

# Make an array of uv coordinates in 3D
coordinates = [(d.uv.x, d.uv.y, 0) for d in uvmap.data]

# Create a jd tree from that
kd = KDTree( len( coordinates ) )

# Populate it
for i, v in enumerate( coordinates ):
    kd.insert( v, i )

# Initialize it
kd.balance()

# Input UV coordinates
x = 0.41
y = 0.96

# Search
coordinate, index, distance = kd.find( (x, y, 0) )

print( coordinate )
print( index ) 
print( distance )

# Corresponding vertex (in the mesh) and its index
vertex_index = obj.data.loops[index].vertex_index
vertex = obj.data.vertices[vertex_index]

print( vertex.index )

Note: there is also a bvhtree version in the blend file. If you have time you could compare the results and perfomence

The main diff between bvh and kd is that bvh will test on faces and kd will test on vertex proximity (so this can be outside the face). I don't know what is important in your context.

In the blend file, there is two script in the text editor 'KDTree' and 'BVHTree' so that you can choose.

Wondering is it worth extending to get all uv's at uv of closest, and the associated verts? — batFINGER, Jul 26 '19 at 07:52
@batFINGER, we'll see if the OP ask about that and what is his goal. In the same spirit I'd first though about bvh raycats which ensures to be inside a face (as kdtree does not). — lemon, Jul 26 '19 at 08:08
While your here, how is your python file io? Mine is crap. Re https://blender.stackexchange.com/questions/145906/reading-text-blocks-from-blends-with-blendfile-py I have the struct TextLine and know where the blocks are, but can't get my head around reading the field string values. Note the blendfile walker module in the same folder. — batFINGER, Jul 26 '19 at 08:16
works great, but it seems I have lost one point, probably because he was to close to another point. How can I get the N closest neighbor with kdtree ? Thanks again good sir. — Edmond Boulet-Gilly, Jul 26 '19 at 08:46
@EdmondBoulet-Gilly Yes. see https://docs.blender.org/api/current/mathutils.kdtree.html#mathutils.kdtree.KDTree.find_n — lemon, Jul 26 '19 at 08:56

Select vertex in UV map based on coordinate x,y

1 Answers1