Converting 3D Geometry Into Displacement Maps
By Neil Blevins
Created On: Jan 25th 2022

There are many techniques and tools for converting 3d Geometry into displacement maps, especially for transferring details from a highres mesh to a lowres mesh in games. This lesson is about a quick and dirty method I've used to convert 3d greebles into displacement maps.

Starship Hulls

Many of you have seen the Starship Hull images I've made, example below...

A lot of people were surprised when I showed that these images weren't 3d geometry or displacement, they mostly used a photoshop trick for shadowing and beveling edges. Read more about it here: Painting Starship Panels In Photoshop

But late last year I decided, just for fun, to make a few similar images that were actual displacement maps. Here's the result...

Here's the displacement map I made...

And the result of the displacement using the map above on a plane...

For the main paneling, I painted displacement values inside of photoshop. But for some of the smaller greebles, like these...

I made 3d geometry, and then converted that geometry into displacement maps, and then added them to my hand painted displacement.

So this lesson will be about how I did that 3d to disp map conversion.

Process

So first I modeled some greebles in 3dsmax (although a similar workflow can be done in pretty much any piece of software), here's an example...

Our goal is to displace this plane into the same shape as the 3d geometry.

So I want to convert the 3d geometry in a displacement map. In a displacement map, the value white means something is high, and a value of black means something is low, with grey values somewhere in between.

So, I take the highres geometry and assign a flat color material with a gradient in the diffuse slot. This could be a Standard material with 100% self illumination, but since I'm using vray, I'm using a VrayLightMtl with the gradient ramp in the color slot.

For the Gradient Ramp map, the only thing I adjusted was the rotation to -90, so my gradient went up and down instead of right to left.

Now I select my 3d geometry and add a Planar uvwMap from the side like this...

Now I assign the flat color material to my 3d geometry, and then render from the Top Viewport, and I get a result like this...

That's my displacement map for my plane, again, white are the highest areas, black the lowest, and the color comes from that gradient projected from the side.

So I hide my 3d geometry, unhide my plane, and assign a turbosmooth to the plane, setting it to add a bunch of extra faces...

Then I add a displace Modifier, and place my rendered displacement map on the map slot...

I then render my plane, which looks sorta right, but it's too flat for some reason.

This is because our Strength (or in other words, height) is set wrong for the displace modifier. It's using the default of 1.0. What should be the correct strength? I could eyeball it, but let's find out more directly. If I select my original 3d geometry, go to the Utilities tab, and go to the Measure tool, I see that my original geometry is 8.613 units in the Z dimension...

So my original object is 8.613 units high. Which means the value of black in my displacement map represents a height of 0, and a value of white represents 8.613 units high. So to get an identical height with my displacement, I need to change my Displacement strength from the default of 1.0 to 8.613. Now lets check the render...

One nice thing about the Displace Modifier is you can see the result in the viewport. Here's me double checking that the height of the displacement matches the height of the geometry in the front viewport. The purple is my 3d Geometry, the white is my displaced plane. Looks pretty much identical...

But if you don't care about seeing the result in the viewport, and you're a vray user, you could also use the vray displacement modifier instead of the turbosmooth and displace modifier. Here's the settings I used to get identical results...

Adjust the edge length down to get a cleaner but slower to render result.

Conclusion

If you need to make a really complex displacement map with overhangs or of a really complex surface, there are other better techniques out there. But if your needs are simple, like adding pebbles on a flat terrain or some vents to an enormous scifi megastructure, this technique may be the way to go. So give it a try!

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