Align to face normal vector

Question

Help me rotation new object by normal a face other object. I have code that works half. The axes at the selected polygon and the new object must be the same

code - http://pasteall.org/632513/python

scene - http://pasteall.org/blend/index.php?id=48131

code - http://pasteall.org/632513/python

scene - http://pasteall.org/blend/index.php?id=48131

The MathViz addon is very useful to visualize matrices, quats and vecs. Is the normal axis in image above in local or global coordinates? — batFINGER, Oct 25 '17 at 04:14
I do not understand ... The manipulator in normal mode https://i.imgur.com/PnOisQi.png I need the local axis of the new object to look the same as this normal — Влад Киндюшов, Oct 25 '17 at 08:51
if you encounter some issue with 2.8 replace every "*" with "@" https://wiki.blender.org/wiki/Reference/Release_Notes/2.80/Python_API — Fox, Apr 24 '19 at 00:17

batFINGER · Accepted Answer · 2017-10-26T06:40:47.273

7

Align to vector using Vector.rotation_difference(v)

Altered the script from this answer to find the quaternion rotation difference between the local z axis of the edit mesh and the normal of its selected (active) face.

Run script with target object in edit mode, one face selected and active. An object in scene named "Cube.001" will be located at face centre and oriented by face normal.

import bpy
from mathutils import Matrix, Vector
import bmesh
context = bpy.context
obj = context.edit_object
mw = obj.matrix_world.copy()
bm = bmesh.from_edit_mesh(obj.data)
# for this example jmake a face active
face = bm.select_history.active
o = face.calc_center_median()
# calculate the axis dif in local coords

axis_src = face.normal
# local z-axis
axis_dst = Vector((0, 0, 1))

matrix_rotate = mw.to_3x3()
matrix_rotate = matrix_rotate * axis_src.rotation_difference(axis_dst).to_matrix()
matrix_translation = Matrix.Translation(mw * o) # 

obj2 = context.scene.objects.get("Cube.001")
obj2.matrix_world = matrix_translation * matrix_rotate.to_4x4()

Result of script. Moved cube in edit mode, showing local coords.

edited Oct 26 '17 at 06:40

answered Oct 25 '17 at 10:12

batFINGER

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Sumptuously! That's what I needed. Many thanks – Влад Киндюшов Oct 25 '17 at 10:23
Look at the top polygon does not work. https://i.imgur.com/JqYfL7F.gifv – Влад Киндюшов Oct 25 '17 at 19:59
@ВладКиндюшов whoops, should have checked that. Anyhoo, think I have it now. – batFINGER Oct 26 '17 at 06:32
I add ".inverted()" in to "axis_src.rotation_difference(axis_dst).to_matrix()" line 18 https://i.imgur.com/lSksTnW.gifv – Влад Киндюшов Oct 27 '17 at 19:40
But this is a bad solution for the cube. Perhaps there is a way that will work in both cases.https://i.imgur.com/DFP8mXu.png – Влад Киндюшов Oct 27 '17 at 20:26
And in some cases it does not work at all. Scene - https://drive.google.com/file/d/0B44RnfYzKt3cZXdaX01wMGdsWWc/view?usp=drivesdk GIF - https://i.imgur.com/5MYYzIb.gifv – Влад Киндюшов Oct 27 '17 at 20:57
Need to get some zzzzz's will get back to it. Will look at logic, might have to align to two axes. Both methods align to normal Ok. align to normal with track_quot track to z and y up, and then align to x or y local with rot_dif. – batFINGER Oct 27 '17 at 21:16
2

Think using BMFace.calc_tangent will give us the other alignment vector (that the normal axes are showing) to align object x axis to. (can make the rotation matrix with Matrix(norm, tangent, norm.cross(tangent)). Apologies. – batFINGER Oct 28 '17 at 00:07
Look. I want to make the similar addon for Blender - https://vimeo.com/36732689. If you are interested and would like to give me a little help than here is my email address Darcvizer@gmail.com It's going to be free. – Влад Киндюшов Oct 28 '17 at 00:20
Forgive me but could not give an example in the form of code? I do not how can I tell him how to work... – Влад Киндюшов Oct 29 '17 at 00:12
Sadly it does not work in Blender 3.1 anymore, I get the following error:
TypeError: Element-wise multiplication: not supported between 'Matrix' and 'Vector' types
– Lala_Ghost Apr 06 '22 at 09:35
does not work for me – Phil Apr 26 '22 at 07:05

score 6 · Answer 2 · answered Nov 09 '17 at 18:39

Alexander Nedovizin solved this problem

import bpy
from mathutils import Matrix, Vector
import bmesh
context = bpy.context
obj = context.edit_object
mw = obj.matrix_world.copy()
bm = bmesh.from_edit_mesh(obj.data)
face = bm.select_history.active
o = face.calc_center_median()

axis_src = face.normal
axis_src2 = face.calc_tangent_edge()
axis_dst = Vector((0, 0, 1))
axis_dst2 = Vector((0, 1, 0))

vec2 = axis_src * obj.matrix_world.inverted()
matrix_rotate = axis_dst.rotation_difference(vec2).to_matrix().to_4x4()

vec1 = axis_src2 * obj.matrix_world.inverted()
axis_dst2 = axis_dst2*matrix_rotate.inverted()
mat_tmp = axis_dst2.rotation_difference(vec1).to_matrix().to_4x4()
matrix_rotate = mat_tmp*matrix_rotate
matrix_translation = Matrix.Translation(mw * o) #

obj2 = context.scene.objects.get("Cube.001")
obj2.matrix_world = matrix_translation * matrix_rotate.to_4x4()

From 2.8+ version you have to change replace "mw * o" with "mw @ o". But it still does not work for Blender 3.2. — Lala_Ghost, Aug 10 '22 at 07:56
Lala_Ghost you need to replace all * with @. This solution is the only one that worked for me. — APEC, Mar 13 '23 at 10:45

score 2 · Answer 3 · edited Oct 12 '22 at 16:10

I had to modify Alexander's solution a bit to make it work:

import bpy
import mathutils
C = bpy.context
cursor = C.scene.cursor
obj = C.active_object
p = obj.data.polygons
#get the normal and center of the selected face
normal = obj.data.polygons[p.active].normal
center = obj.data.polygons[p.active].center
#generate a quaternion rotation from the normal vector
up = normal.to_track_quat('X', 'Y')
print(up)
#set the cursor to the center location and rotate it to match the up vector
cursor.location = center
cursor.rotation_quaternion = up
cursor.rotation_quaternion.to_euler()
#get the object world matrix
mat = obj.matrix_world
print(mat)
#generate the location and rotation
rot = cursor.rotation_quaternion.to_euler()
print(rot)
loc = mat @ cursor.location.copy()
obj2 = C.scene.objects.get("Cube.001")
obj2.location = loc
obj2.rotation_euler = rot
#bpy.ops.object.mode_set(mode='OBJECT')
#bpy.ops.mesh.primitive_cube_add(location = loc, size = 0.1, rotation =rot)
#bpy.ops.object.empty_add(type='ARROWS',location = loc, rotation =rot)

Align to face normal vector

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