Copying a meshes intersecting outline from the top down view

Question

I have a sliced shape that I would like to copy it's outline as it's seen from the top down view (looking straight down on it).

Example: I have an equation that is sliced by a plane using the Intersect option of the Boolean modifier.

I then want to copy just the outline / Intersection (the "warped" egg shape circled in red) that is created when looking at it from the top down view.

I was looking at the Knife project tool but I want the projection of top down view of a slice.

I feel like I'm over thinking it. I'm willing to try a different solution.

As in copy the edge ring, separate, and shrinkwrap project in Z onto an XY plane or via code set the z coord of each ring vert to a constant.? — batFINGER, Feb 28 '21 at 09:39
@batFINGER Yes to the first part project Z onto XY. Not sure what the 2nd "via code set the z cord to a constant" it sounds intriguing (not sure what that will do or how to do that). — Rick T, Feb 28 '21 at 09:43
same as first. XY ground plane is Z=0 hence any coord on that plane is (x, y, 0) — batFINGER, Feb 28 '21 at 09:45
@batFINGER sounds quicker. I duplicated the edge loop but how does one set each edge to zero so it mimics the "egg" shape? — Rick T, Feb 28 '21 at 09:53
set the vert coords. for v in youredgeloopobject.data.vertices: v.co.z = 0 (This assumes that the mesh has no loc rot & unit scale, ie local and global coords same) Somewhat related https://blender.stackexchange.com/questions/132925/planetary-system-simulation-with-real-orbital-datas — batFINGER, Feb 28 '21 at 09:56
@RobinBetts I knew I was over thinking...At-least I learned new ways to do it. Thanks. — Rick T, Feb 28 '21 at 17:00

score 2 · Accepted Answer · answered Feb 28 '21 at 10:43

Via a script.

A "conic section script".

Define a plane via its global location and normal. For example add a plane named "Plane" aligned to cut

>>> C.object
bpy.data.objects['Plane']

plane_co Global coordinate.

>>> C.object.matrix_world.translation
Vector((0.0, 0.0, 0.0))

plane_no Global normal. (its rotation x z axis)

>>> C.object.matrix_world.to_3x3() @ Vector((0, 0, 1))
Vector((0.8242384195327759, -0.06781885027885437, 0.5621669292449951))

Running this script will bisect the context object (with modifiers and shapekeys applied) using the plane coordinates supplied and create a new segment object.

import bpy
import bmesh
from mathutils import Matrix
from bpy import context
cutting plane coords and normal (global)
plane_co = (0, 0, 0)
plane_no = (1, 1, 1)
project_to_ground = True
ob = context.object
object with modifiers shapekeys applied.
bm = bmesh.new()
bm.from_object(
        ob, 
        context.evaluated_depsgraph_get()
        )
bm.transform(ob.matrix_world)
bmesh.ops.bisect_plane(
        bm,
        geom=sum((bm.verts[:], bm.edges[:], bm.faces[:]), []),
        plane_no=plane_no,
        plane_co=plane_co,
        clear_inner=True,
        clear_outer=True,
        )
me = bpy.data.meshes.new(f"{ob.name}_Section")
bm.to_mesh(me)
if project_to_ground:
    me.transform(Matrix.Scale(0, 4, (0, 0, 1)))
new_ob = bpy.data.objects.new(f"{ob.data.name}_Section", me)
context.collection.objects.link(new_ob)

How to extract side-view outline (e.g. top view) of a 3D object to 2D surface?

Copying a meshes intersecting outline from the top down view

1 Answers1

cutting plane coords and normal (global)

object with modifiers shapekeys applied.