Retopologize already retopologized model to a lower poly variant

Latiro

Hello everyone,

First off: Sorry if this question is simple/obvious. I did some googling today and most likely I just searched for the wrong things, but I couldn't find an answer.

My question is simple: Is it possible to retopologize/decimate a low-poly version of a high-poly mesh to an even lower poly version and keeping the normal map? The situation is the following: I have a 30k poly version of a 2 000 000 000 3D-scan, which already has a nice unwrap and is cleaned up. For my purposes, though, I need to get the object down to ~ 2k, which I thought retopologization would be good for. How can I do that, without losing the baked normal map of the 30k version?

Thank you advance for help!

All the best,

Nicolas

Obscura

So you want to use the normalmap of the 30k mesh on the 2k mesh? That won't work well, especially because you would use a lot less geo. It would give horrible results. Because the mesh normals and the information in normal map wouldn't match.

Latiro

Hi Obscura,

thanks for your answer. So basically you're saying that's not possible, right? I would probably need to do another, new retopo from the High-Poly-Mesh?

sprunghunt

In 3dsmax you can bake from the 30k mesh to a lower polygon mesh if you apply the existing normalmap to the 30k mesh. It'll take those normals into account when you bake between the two meshes.

Obscura

You can do an automatic retopo somehow, or you can retopo with hand, but you will need to bake a new normalmap.

Latiro

"In 3dsmax you can bake from the 30k mesh to a lower polygon mesh if you apply the existing normalmap to the 30k mesh. It'll take those normals into account when you bake between the two meshes."

That's valuable information, thank you! Could you recommend any good tutorials that walk through the process of baking in 3dsMax?

Lt_Commander

This tutorial is pretty extensive and covers what you need:

[ame]https://www.youtube.com/watch?v=frPuPNA0daY[/ame]

skankerzero

Is the 2k mesh going to be close to the camera? If not then don't worry about how the normal map looks on the 2k model. From a distance you will not be able to tell if something is off.

Heck, from a distance you may not even need the normal map.

remotecrab131

If you use object space normal map, with almost same UV layout, you might end up with an extremely similar looking object. But to be honest, Object space normal map isn't really a popular thing now because it doesn't work well on deformed models. (Thou it would look better than any other types of normal map on a static mesh)


If the normal map isn't baked from a highpoly, then with the same UV layout, you can also get a similar looking lowerpoly object. Baked tangent space normal map restrictively requires a corresponding geometry. If you put it on a even more lower poly model with same UV layout(which is impossible anyway), it will going to look really awkward.

Latiro

I planned on using Tangent-Space normals, yes, because the objects will be deformed a lot (Trees). And it will be closed to the camera, so I think the normal map will make a difference. Thanks a lot for all of your answers! I will take a look at the tutorial linked by lt_Commander.