Area of bottom polygons using obj.to_mesh post modifier but without applying it

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First of all, I'm quite new to python so please bear with me if I'm asking dumb questions. I've seen similar questions answered but still can't get where I want.

Say we have an active object in the scene, which is a polyline, which is extruded in z direction and altered with solidify modifier to give it some thickness (like a wall for example). I'm trying to get the summary area of all the bottom faces of the object as visible in the scene without actually applying the modifier. From what I've read it should be possible via obj.to_mesh, but while I can get the area of all faces with sum(f.calc_area(), I'm missing something (possibly obvious) when it comes to getting just the sum of bottom ones.

Here is my attempt:

import bpy
import bmesh

context = bpy.context
scene = context.scene
obj = bpy.context.active_object

# --- get a mesh from the object ---
apply_modifiers = True
settings = 'PREVIEW'
mesh = obj.to_mesh(scene, apply_modifiers, settings)

bm = bmesh.new()
bm.from_mesh(mesh)

for face in bm.faces:

 face_location = face.calc_center_median()

 z = face_location[2]

 bpy.ops.object.mode_set(mode = 'EDIT')

 if z ==0: 

 face.select==True

 bpy.ops.object.mode_set(mode = 'OBJECT')

 area = sum(f.calc_area() for f in bm.faces if f.select)

 print(area)

bm.free()

bpy.data.meshes.remove(mesh)

What I get is value "0" printed out 16 times (for each face in the object I guess as it has 16 faces).
I realise it's probably something trivial I'm missing but maybe someone could please explain it to me?

asked 3 hours ago

MatH

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up vote
1
down vote

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First of all, I'm quite new to python so please bear with me if I'm asking dumb questions. I've seen similar questions answered but still can't get where I want.

Here is my attempt:

import bpy
import bmesh

context = bpy.context
scene = context.scene
obj = bpy.context.active_object

# --- get a mesh from the object ---
apply_modifiers = True
settings = 'PREVIEW'
mesh = obj.to_mesh(scene, apply_modifiers, settings)

bm = bmesh.new()
bm.from_mesh(mesh)

for face in bm.faces:

 face_location = face.calc_center_median()

 z = face_location[2]

 bpy.ops.object.mode_set(mode = 'EDIT')

 if z ==0: 

 face.select==True

 bpy.ops.object.mode_set(mode = 'OBJECT')

 area = sum(f.calc_area() for f in bm.faces if f.select)

 print(area)

bm.free()

bpy.data.meshes.remove(mesh)

asked 3 hours ago

MatH

New contributor

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up vote
1
down vote

favorite

First of all, I'm quite new to python so please bear with me if I'm asking dumb questions. I've seen similar questions answered but still can't get where I want.

Here is my attempt:

import bpy
import bmesh

context = bpy.context
scene = context.scene
obj = bpy.context.active_object

# --- get a mesh from the object ---
apply_modifiers = True
settings = 'PREVIEW'
mesh = obj.to_mesh(scene, apply_modifiers, settings)

bm = bmesh.new()
bm.from_mesh(mesh)

for face in bm.faces:

 face_location = face.calc_center_median()

 z = face_location[2]

 bpy.ops.object.mode_set(mode = 'EDIT')

 if z ==0: 

 face.select==True

 bpy.ops.object.mode_set(mode = 'OBJECT')

 area = sum(f.calc_area() for f in bm.faces if f.select)

 print(area)

bm.free()

bpy.data.meshes.remove(mesh)

asked 3 hours ago

MatH

New contributor

First of all, I'm quite new to python so please bear with me if I'm asking dumb questions. I've seen similar questions answered but still can't get where I want.

Here is my attempt:

import bpy
import bmesh

context = bpy.context
scene = context.scene
obj = bpy.context.active_object

# --- get a mesh from the object ---
apply_modifiers = True
settings = 'PREVIEW'
mesh = obj.to_mesh(scene, apply_modifiers, settings)

bm = bmesh.new()
bm.from_mesh(mesh)

for face in bm.faces:

 face_location = face.calc_center_median()

 z = face_location[2]

 bpy.ops.object.mode_set(mode = 'EDIT')

 if z ==0: 

 face.select==True

 bpy.ops.object.mode_set(mode = 'OBJECT')

 area = sum(f.calc_area() for f in bm.faces if f.select)

 print(area)

bm.free()

bpy.data.meshes.remove(mesh)

scripting measurement

asked 3 hours ago

MatH

New contributor

asked 3 hours ago

MatH

New contributor

asked 3 hours ago

MatH

New contributor

asked 3 hours ago

MatH

asked 3 hours ago

MatH

New contributor

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3 Answers
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I guess, you are getting zero because the face.select is not assigned value True, but is being checked for condition True (face.select == True). Also if you are interested only in bottom faces, i.e faces with all vertices having z coordinate value zero, then checking for median z coordinate may not work in all cases. There could be faces with median z at zero but vertices lying on either side of x-y plane.
I can think of the following alternative (I am open to critique and corrections as I am also comparatively new to blender :)

import bpy
import bmesh


bm = bmesh.new()
#bm = bmesh.from_edit_mesh(bpy.context.active_object.data) (without modifier)
bm.from_object(bpy.context.active_object, bpy.context.scene)

#Floats are not always absolute zero, so comparing with a tolerance
total_area = sum(f.calc_area() for f in bm.faces if len([v for v in f.verts if v.co[2] < 0.0001 and v.co[2] > -0.0001]) == len(f.verts)) 
print('total area:', total_area)

bm.free()

answered 2 hours ago

Blender Dadaist

3117

Upvoted. Suggestion: if all(abs(v.co.z) < 0.0001 for v in f.verts)
â€“Â batFINGER
1 hour ago

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up vote
1
down vote

Use the face normal as test for bottom face.

Note: Between starting this answer, getting sidetracked, and posting another similar answer has been posted using bmesh from object.

CHecking that a local coordinate z is at some level is limiting.
If the mesh is as mentioned simply a wall can get the bottom faces by testing if the face normal points down (or close enough (within 4 degrees).

import bpy
import bmesh
from mathutils import Vector
from math import radians

context = bpy.context
scene = context.scene
ob = context.object

bm = bmesh.new()
bm.from_object(ob, scene)
down = Vector((0, 0, -1))
area = sum(f.calc_area() for f in bm.faces 
 if f.normal.angle(down) < radians(4))

print(area)
bm.free()

answered 1 hour ago

batFINGER

20k32060

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I assume this behaviour is caused by an inconsistent selection state when you only select the face but not the respective vertices and edges. As a result, something like print([f.select for f in bm.faces]) returns a list of False values.

Using the function BMFace.select_set instead of setting BMFace.select will Ã¢Â€Âœupdate the selection state of assosiated geometryÃ¢Â€Â. BMFace.select then will also return True for these faces.

 # snip
 if z == 0: 
 face.select_set(True)
 # snip

Apart from that, I guess you should unindent the area calculation so it's outside of the for face in bm.faces loop. And switching between object and edit mode is not necessary here:

import bpy
import bmesh

context = bpy.context
scene = context.scene
obj = bpy.context.active_object

# --- get a mesh from the object ---
apply_modifiers = True
settings = 'PREVIEW'
mesh = obj.to_mesh(scene, apply_modifiers, settings)

bm = bmesh.new()
bm.from_mesh(mesh)

for face in bm.faces:
 face_location = face.calc_center_median()
 z = face_location[2]

 if z == 0: 
 face.select_set(True)

area = sum(f.calc_area() for f in bm.faces if f.select)
print(area)

bm.free()
bpy.data.meshes.remove(mesh)

answered 2 hours ago

binweg

1,9311412

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3 Answers
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3 Answers
3

active

oldest

votes

up vote
1
down vote

accepted

import bpy
import bmesh


bm = bmesh.new()
#bm = bmesh.from_edit_mesh(bpy.context.active_object.data) (without modifier)
bm.from_object(bpy.context.active_object, bpy.context.scene)

#Floats are not always absolute zero, so comparing with a tolerance
total_area = sum(f.calc_area() for f in bm.faces if len([v for v in f.verts if v.co[2] < 0.0001 and v.co[2] > -0.0001]) == len(f.verts)) 
print('total area:', total_area)

bm.free()

answered 2 hours ago

Blender Dadaist

3117

Upvoted. Suggestion: if all(abs(v.co.z) < 0.0001 for v in f.verts)
â€“Â batFINGER
1 hour ago

add a commentÂ |Â

up vote
1
down vote

accepted

import bpy
import bmesh


bm = bmesh.new()
#bm = bmesh.from_edit_mesh(bpy.context.active_object.data) (without modifier)
bm.from_object(bpy.context.active_object, bpy.context.scene)

#Floats are not always absolute zero, so comparing with a tolerance
total_area = sum(f.calc_area() for f in bm.faces if len([v for v in f.verts if v.co[2] < 0.0001 and v.co[2] > -0.0001]) == len(f.verts)) 
print('total area:', total_area)

bm.free()

answered 2 hours ago

Blender Dadaist

3117

Upvoted. Suggestion: if all(abs(v.co.z) < 0.0001 for v in f.verts)
â€“Â batFINGER
1 hour ago

add a commentÂ |Â

up vote
1
down vote

accepted

import bpy
import bmesh


bm = bmesh.new()
#bm = bmesh.from_edit_mesh(bpy.context.active_object.data) (without modifier)
bm.from_object(bpy.context.active_object, bpy.context.scene)

#Floats are not always absolute zero, so comparing with a tolerance
total_area = sum(f.calc_area() for f in bm.faces if len([v for v in f.verts if v.co[2] < 0.0001 and v.co[2] > -0.0001]) == len(f.verts)) 
print('total area:', total_area)

bm.free()

answered 2 hours ago

Blender Dadaist

3117

import bpy
import bmesh


bm = bmesh.new()
#bm = bmesh.from_edit_mesh(bpy.context.active_object.data) (without modifier)
bm.from_object(bpy.context.active_object, bpy.context.scene)

#Floats are not always absolute zero, so comparing with a tolerance
total_area = sum(f.calc_area() for f in bm.faces if len([v for v in f.verts if v.co[2] < 0.0001 and v.co[2] > -0.0001]) == len(f.verts)) 
print('total area:', total_area)

bm.free()

answered 2 hours ago

Blender Dadaist

3117

answered 2 hours ago

Blender Dadaist

3117

answered 2 hours ago

Blender Dadaist

3117

answered 2 hours ago

Blender Dadaist

3117

Upvoted. Suggestion: if all(abs(v.co.z) < 0.0001 for v in f.verts)
â€“Â batFINGER
1 hour ago

add a commentÂ |Â

Upvoted. Suggestion: if all(abs(v.co.z) < 0.0001 for v in f.verts)
â€“Â batFINGER
1 hour ago

Upvoted. Suggestion: if all(abs(v.co.z) < 0.0001 for v in f.verts)
â€“Â batFINGER
1 hour ago

add a commentÂ |Â

up vote
1
down vote

Use the face normal as test for bottom face.

Note: Between starting this answer, getting sidetracked, and posting another similar answer has been posted using bmesh from object.

import bpy
import bmesh
from mathutils import Vector
from math import radians

context = bpy.context
scene = context.scene
ob = context.object

bm = bmesh.new()
bm.from_object(ob, scene)
down = Vector((0, 0, -1))
area = sum(f.calc_area() for f in bm.faces 
 if f.normal.angle(down) < radians(4))

print(area)
bm.free()

answered 1 hour ago

batFINGER

20k32060

add a commentÂ |Â

up vote
1
down vote

Use the face normal as test for bottom face.

Note: Between starting this answer, getting sidetracked, and posting another similar answer has been posted using bmesh from object.

import bpy
import bmesh
from mathutils import Vector
from math import radians

context = bpy.context
scene = context.scene
ob = context.object

bm = bmesh.new()
bm.from_object(ob, scene)
down = Vector((0, 0, -1))
area = sum(f.calc_area() for f in bm.faces 
 if f.normal.angle(down) < radians(4))

print(area)
bm.free()

answered 1 hour ago

batFINGER

20k32060

add a commentÂ |Â

up vote
1
down vote

Use the face normal as test for bottom face.

Note: Between starting this answer, getting sidetracked, and posting another similar answer has been posted using bmesh from object.

import bpy
import bmesh
from mathutils import Vector
from math import radians

context = bpy.context
scene = context.scene
ob = context.object

bm = bmesh.new()
bm.from_object(ob, scene)
down = Vector((0, 0, -1))
area = sum(f.calc_area() for f in bm.faces 
 if f.normal.angle(down) < radians(4))

print(area)
bm.free()

answered 1 hour ago

batFINGER

20k32060

Use the face normal as test for bottom face.

Note: Between starting this answer, getting sidetracked, and posting another similar answer has been posted using bmesh from object.

import bpy
import bmesh
from mathutils import Vector
from math import radians

context = bpy.context
scene = context.scene
ob = context.object

bm = bmesh.new()
bm.from_object(ob, scene)
down = Vector((0, 0, -1))
area = sum(f.calc_area() for f in bm.faces 
 if f.normal.angle(down) < radians(4))

print(area)
bm.free()

answered 1 hour ago

batFINGER

20k32060

answered 1 hour ago

batFINGER

20k32060

answered 1 hour ago

batFINGER

20k32060

answered 1 hour ago

batFINGER

20k32060

add a commentÂ |Â

up vote
0
down vote

 # snip
 if z == 0: 
 face.select_set(True)
 # snip

Apart from that, I guess you should unindent the area calculation so it's outside of the for face in bm.faces loop. And switching between object and edit mode is not necessary here:

import bpy
import bmesh

context = bpy.context
scene = context.scene
obj = bpy.context.active_object

# --- get a mesh from the object ---
apply_modifiers = True
settings = 'PREVIEW'
mesh = obj.to_mesh(scene, apply_modifiers, settings)

bm = bmesh.new()
bm.from_mesh(mesh)

for face in bm.faces:
 face_location = face.calc_center_median()
 z = face_location[2]

 if z == 0: 
 face.select_set(True)

area = sum(f.calc_area() for f in bm.faces if f.select)
print(area)

bm.free()
bpy.data.meshes.remove(mesh)

answered 2 hours ago

binweg

1,9311412

add a commentÂ |Â

up vote
0
down vote

 # snip
 if z == 0: 
 face.select_set(True)
 # snip

Apart from that, I guess you should unindent the area calculation so it's outside of the for face in bm.faces loop. And switching between object and edit mode is not necessary here:

import bpy
import bmesh

context = bpy.context
scene = context.scene
obj = bpy.context.active_object

# --- get a mesh from the object ---
apply_modifiers = True
settings = 'PREVIEW'
mesh = obj.to_mesh(scene, apply_modifiers, settings)

bm = bmesh.new()
bm.from_mesh(mesh)

for face in bm.faces:
 face_location = face.calc_center_median()
 z = face_location[2]

 if z == 0: 
 face.select_set(True)

area = sum(f.calc_area() for f in bm.faces if f.select)
print(area)

bm.free()
bpy.data.meshes.remove(mesh)

answered 2 hours ago

binweg

1,9311412

add a commentÂ |Â

up vote
0
down vote

 # snip
 if z == 0: 
 face.select_set(True)
 # snip

Apart from that, I guess you should unindent the area calculation so it's outside of the for face in bm.faces loop. And switching between object and edit mode is not necessary here:

import bpy
import bmesh

context = bpy.context
scene = context.scene
obj = bpy.context.active_object

# --- get a mesh from the object ---
apply_modifiers = True
settings = 'PREVIEW'
mesh = obj.to_mesh(scene, apply_modifiers, settings)

bm = bmesh.new()
bm.from_mesh(mesh)

for face in bm.faces:
 face_location = face.calc_center_median()
 z = face_location[2]

 if z == 0: 
 face.select_set(True)

area = sum(f.calc_area() for f in bm.faces if f.select)
print(area)

bm.free()
bpy.data.meshes.remove(mesh)

answered 2 hours ago

binweg

1,9311412

 # snip
 if z == 0: 
 face.select_set(True)
 # snip

Apart from that, I guess you should unindent the area calculation so it's outside of the for face in bm.faces loop. And switching between object and edit mode is not necessary here:

import bpy
import bmesh

context = bpy.context
scene = context.scene
obj = bpy.context.active_object

# --- get a mesh from the object ---
apply_modifiers = True
settings = 'PREVIEW'
mesh = obj.to_mesh(scene, apply_modifiers, settings)

bm = bmesh.new()
bm.from_mesh(mesh)

for face in bm.faces:
 face_location = face.calc_center_median()
 z = face_location[2]

 if z == 0: 
 face.select_set(True)

area = sum(f.calc_area() for f in bm.faces if f.select)
print(area)

bm.free()
bpy.data.meshes.remove(mesh)

answered 2 hours ago

binweg

1,9311412

answered 2 hours ago

binweg

1,9311412

answered 2 hours ago

binweg

1,9311412

answered 2 hours ago

binweg

1,9311412

add a commentÂ |Â

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