Increase object size/dimension across two axies, while keeping proportions

Question

I am wondering if there is some easy way of quickly scaling an object across two axies (X, Y) while keeping the proportions of the object intact. It's hard to describe so I'll try using some pictures.

This is the object I want to scale:

When I scale it along the X and Y axies, this is the result:

Now, what I want to achieve is the walls of the object being spread out more, giving it a larger center area, but retaining the proportions of the walls, like this:

I created the final picture by tediously having to scale all the individual edge loops to get it looking somewhat right. So I was wondering if there is a better way of achieving this, a good workflow? I hope the question is clear. Cheers.

Answer 1

Close, but only in this case

Select these vertices/edges (you can select one group of the 8, then do Shift+G --> select similar length:

Scale along the two axes that you want in bounding box pivot mode. Then switch to individual origins and scale in the opposite direction with only these vertices selected.

Python Script

It looks like you are only wanting to move each vertex a constant distance from the center. With normal scaling from a point p, a vertex 2 meters from p will move twice as much distance as a vertex 1 meter from p. This small snippet of Python code will not do this, but rather move each vertex a constant addend, not factor, of the radius.

Note: This script scales from the object's origin. Also, you should be in object mode to run it.

import bpy
import bmesh
from math import sqrt

scale = 2  # scale variable

# prepare bmesh
mesh = bpy.context.object.data
bm = bmesh.new()
bm.from_mesh(mesh)

for v in bm.verts:
    pos = v.co.xyz

    # r = sqrt(x^2 + y^2 + z^2)
    radius = sqrt(
        pow(pos.x, 2) + 
        pow(pos.y, 2) +
        pow(pos.z, 2))

    a = (radius + scale) / radius

    # modify the two axes you want
    pos.x *= a
    pos.y *= a

    # apply new position
    v.co.xyz = pos

# make the bmesh the object's mesh
bm.to_mesh(mesh)  
bm.free()

Answer 2

I would think if you go into Edit mode, just select the bottom polygons, then turn on Proportional editing - you'd get your desired effect.

Once you scale, scroll the middle mouse up or down, to dial in the exact level of influence on the outer walls.

Answer 3

1. CtrlAltU > Add-ons, enable the 'Offset Edges' Add-on.

2. Select all the circumferential edges.

3. In the 'Offset Edges' panel, select the 'Move' option.