How to place objects on the center of the ground plane via python?

Question

I put a model at the center of the scene using this method:

bpy.ops.object.origin_set(type="GEOMETRY_ORIGIN")

but I can't put model over the scene after this command. Because it is not at the center of Z axis.

e.g.: when comman is executed model location looks like this.

I thought that command

bpy.ops.object.origin_set(type="GEOMETRY_ORIGIN")

will put model to the center about all axis, and I can just pick it up at half height

obj.location[2] += obj.dimensions[2]/2

but after this I had:

How can I find this offset value?

Answer 1

The position of the object is defined by it's origin point. If you import a model from another 3d package by using an exchange format like .obj or .fbx, the origin is typically at (0,0,0):

In order to align an object directly to the ground plane:

1. Move the object to the origin (to make sure the object is perfectly centered)
2. Iterate through the geometry to find the minimum z location value of all verticies
3. Place the 3d Cursor to the minimum z location value
4. Set the Origin to 3d Cursor
5. Move the object to (0,0,0)

Suzanne aligned to the center of the ground plane

import bpy

# get the current object
current_obj = bpy.context.active_object 

# get the scene
scene = bpy.context.scene

# set geometry to origin
bpy.ops.object.origin_set(type="GEOMETRY_ORIGIN")

zverts = []

# get all z coordinates of the vertices
for face in current_obj.data.polygons:
    verts_in_face = face.vertices[:]
    for vert in verts_in_face:
        local_point = current_obj.data.vertices[vert].co
        world_point = current_obj.matrix_world * local_point
        zverts.append(world_point[2])

# set the minimum z coordinate as z for cursor location
scene.cursor_location = (0, 0, min(zverts))

# set the origin to the cursor
bpy.ops.object.origin_set(type="ORIGIN_CURSOR")

# set the object to (0,0,0)
current_obj.location = (0,0,0)

# reset the cursor
scene.cursor_location = (0,0,0)

Answer 2

The Python BPY solution above is great, thanks for that.

I wanted to add another method, if you wanted to use Nodes, such as Sverchok Add-On, you can use Bounding Box, halfed distance of the height to sort of move the object (with pivot already on center) to the ground.

GIST: https://gist.github.com/144648e89f48699be3b7fccf951e1d19

I tested different scenario.

Hope this is useful.