PERPdemo.py

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

obj = bpy.context.object
me = obj.data
bm = bmesh.from_edit_mesh(me)

verts = [v for v in bm.verts if (v.select and not v.hide)]

#if not len(verts) == 2:
#    msg = "select two vertices"
#    self.report({"WARNING"}, msg)
#    return

v1, v2 = [v.co for v in verts]
print('vectors found:\n', v1, '\n', v2)

## test if shared z values
#if not (v1.z == v2.z):
#    msg = "vert must share at least the z component"
#    self.report({"WARNING"}, msg)
#    return
amt = (0, 0, math.pi/2)
eul = mathutils.Euler(amt, 'XYZ')

mid_vec = v1.lerp(v2, 0.5)
perp_vec = (v1-mid_vec)
perp_vec.rotate(eul)
pt1 = mid_vec + perp_vec
pt2 = mid_vec - perp_vec

# get pt and pick fartest vertex from (projected) intersections
vec1 = bm.verts.new(pt1)
vec2 = bm.verts.new(pt2)
bm.edges.new((vec1, vec2))
bmesh.update_edit_mesh(me)