I’ve tried to do perfect circled arch, around 3d cursor, with already existing vertices, and found, that it’s not so easy to align vertices not in the sphere or circle, but just a segment of it.

So I’ve created my own script to fix that.

```
import bpy
def calc_center(selectedVerts):
median_point = bpy.context.scene.cursor.location
#median_point.y = selectedVerts[0].co.y
return median_point
def calc_distance(center, vertex):
return (vertex.co - center).length
def calc_new_position(center, vertex, length):
vec_normalized = vertex.co-center
vec_normalized.normalize()
return center + vec_normalized * length
def set_new_position(vertex, position):
print (vertex.co - position)
vertex.co = position
def make_arch():
mode = bpy.context.active_object.mode
bpy.ops.object.mode_set(mode='OBJECT')
selectedVerts = [v for v in bpy.context.active_object.data.vertices if v.select]
print("selected {} vertexes", len(selectedVerts))
median_point = calc_center(selectedVerts)
length = map(lambda x: calc_distance(median_point, x), selectedVerts)
sum_length = sum(length)
median_length = sum_length/len(selectedVerts)
for v in selectedVerts:
set_new_position(v, calc_new_position(median_point, v, median_length))
bpy.ops.object.mode_set(mode=mode)
```

By calling **make_arch()** you can line up to arc org circle segment selected vertices. So it’s easy to adjust them to circle by using array modifier and so on. Position of 3D cursor can affect strongly on resulting position, so be careful with lining it in very begining.