Get center of geometry of an object

Question

With Object > Transform > Origin to Geometry, an object's origin is moved to its geometry's center. How can I get this center in script? I don't want to move its origin, I just need to get its center.

Answer 1

Here's a low level way to calculate the bounding box center of an object:

import bpy

o = bpy.context.object
vcos = [ o.matrix_world * v.co for v in o.data.vertices ]
findCenter = lambda l: ( max(l) + min(l) ) / 2

x,y,z  = [ [ v[i] for v in vcos ] for i in range(3) ]
center = [ findCenter(axis) for axis in [x,y,z] ]

print( center )

EDITED:

@batFINGER proposed a much shorter and more efficient way to calculate the bounding box center (thanks!). Multiplication by the object's world matrix gives a global coordinate:

import bpy
from mathutils import Vector
o = bpy.context.object
local_bbox_center = 0.125 * sum((Vector(b) for b in o.bound_box), Vector())
global_bbox_center = o.matrix_world * local_bbox_center

It will find the center of the active object. The bounding box center (or "range" center) is calculated as the center between the minimum and maximum value in each axis.

It does not give you the same result that origin to geometry or origin to center of mass gives, but it is the center.

Answer 2

You can set the cursor to the object position, then set the origin to geometry, take this position and set back the origin to the cursor.

cursorLoc = bpy.context.scene.cursor_location.copy()
bpy.context.scene.cursor_location = obj.location
bpy.ops.object.origin_set(type='ORIGIN_GEOMETRY')
loc = obj.location.copy()
bpy.ops.object.origin_set(type='ORIGIN_CURSOR')
bpy.context.scene.cursor_location = cursorLoc

Here loc contains the geometry center position.

Edit : following some tests, it seems that 'origin to geometry center' is the average value of the vertices coordinates, so:

x, y, z = [ sum( [v.co[i] for v in obj.data.vertices] ) for i in range(3)]
count = float(len(obj.data.vertices))
center = obj.matrix_world * (Vector( (x, y, z ) ) / count )

For Blender 3.2 (use ops):

import bpy
def get_objcenter(obj):
    # save cursor location
    cursorLoc = bpy.context.scene.cursor.location.copy()
    #To undo this later, the cursor must be aligned with the location of the object.
    bpy.context.scene.cursor.location = obj.location
    # Align the object's origin with the object's center.
    bpy.ops.object.origin_set(type='ORIGIN_GEOMETRY')
    # Master the center vector
    loc = obj.location.copy()
    # Align the object's origin with the object's location for later undo
    bpy.ops.object.origin_set(type='ORIGIN_CURSOR')
    # Undo the cursor location
    bpy.context.scene.cursor.location = cursorLoc
return loc


test
obj= bpy.context.object
print(get_objcenter(obj))

For Blender 3.2 (use mathutils):

import bpy
from mathutils import Vector
def get_objcenter(obj):
    # Total value of each vertex
    x, y, z = [ sum( [v.co[i] for v in obj.data.vertices] ) for i in range(3)]
    # number of vertices
    count = float(len(obj.data.vertices))
    # Divide the sum of each vector by the number of vertices
    # And make the position a world reference.
    center = obj.matrix_world @ (Vector( (x, y, z ) ) / count )
return center


test
obj = bpy.context.object
print(get_objcenter(obj))