Read particular edge length and save its values as UV coordinates

Question

Need help with creation of the script which could read particular edge length of the rectangular planes. Need to recognize which length is the width (just edges pointed in x) and which one height(just edges pointed in z). These values i would like to store as the width and height variables(dimension of the plane). All planes are oriented in the same direction (width will be always x and height always z) but there are thousands of them. Then i would need to use these width and height as the coordinates for UVs for each point of each polygon. x=width, y=height so i will get just one single point for whole rectangle. I tried to investigate how it would be possible and i found two scripts one for reading lengths for all edges and second one for writing UV coordinates. Everything could be possible to do just in edit mode after i will choose correct UVlayer. The second script works fine for me just i need to implement somehow the recognizin of the length and height values for each rectangle.

Reading edge lengths

import bpy
import bmesh

object = bpy.context.active_object
bm = bmesh.from_edit_mesh(object.data)

for edge in bm.edges:
    length = edge.calc_length()
    print("length:",length)

Writing UV coordinates for each vertex

import bpy
import bmesh

obj = bpy.context.active_object
me = obj.data
bm = bmesh.from_edit_mesh(me) 
    
uv_layer = bm.loops.layers.uv.verify()

# adjust uv coordinates
for face in bm.faces:
    for loop in face.loops:
        loop_uv = loop[uv_layer]
        # use xy position of the vertex as a uv coordinate
        loop_uv.uv = loop.vert.co.x

bmesh.update_edit_mesh(me)

EDIT: I tried to implement this calculation into my code but still i dont know how can i get the desired width and length of the ractangle. In below code a wanted just simply to print these values but without success. Is there something what i missed?

import bpy
import bmesh
import mathutils

obj = bpy.context.active_object
me = obj.data
bm = bmesh.from_edit_mesh(me)
bm.edges.ensure_lookup_table()

x = mathutils.Vector((1,0,0))

for edge in bm.edges:
    edges_x = []
    edges_z = []
    v = edge.verts[0].co - edge.verts[1].co
    if abs(v.dot(x)) < .0001:
        edges_z.append(edge)
    else:
        edges_x.append(edge)
    width = edges_x.calc_length()
    height = edges_z.calc_length()
    print(width)
    print(height)
```

Answer 1

I would try

for face in bm.faces:
    # Compute edge vectors
    e1 = face.verts[1].co - face.verts[0].co
    e2 = face.verts[2].co - face.verts[1].co

    # Decide which is width and which is height
    if abs(e1.x) > abs(e1.z):
        w, h = e1.length, e2.length
    else:
        w, h = e2.length, e1.length

    # Assign UVs 
    for loop in face.loops:
        loop[uv_layer].uv = (w, h)

Answer 2

Assuming that you have applied any rotation and scale to the planes, this code will divide the edges of the planes into those parallel to the X axis and those parallel to the Z axis. (Really, those not parallel to the X axis, but I'm assuming your planes meet your criteria.) If you have not applied rotation and scale, then you need to vector multiply the coordinates of the edges by the object's matrix_world.

See the manual for details on bm.edges

edges = bm.edges
bm.edges.ensure_lookup_table()

x = Vector((1,0,0))
edges_x = []
edges_z = []
for edge in edges:
    v = edge.verts[0].co - edge.verts[1].co
    if abs(v.dot(x)) < .0001:
        edges_z.append(edge)
    else:
        edges_x.append(edge)

This relies on the fact that if two vectors are perpendicular their dot product will be zero. Since we're using floating point numbers, it's not wise to do a direct comparison to 0, so we compare to $epsilon$, here, just a very small number.

Now that you have the two lists of edges you can use them in your UV code as you need them.