How to remove split mesh seams

[Maяcel]

info

Original tutorial here: http://www.twcenter.net/forums/showthread.php?t=368614

the tutorial

Whats This Tutorial about

This tutorial will show you how to get rid of those annoying seams you get when splitting a part of a mesh. This tutorial will explain why it happens, and how you can fix it.

To illustrate the problem, here's a picture showing a unit for the M2TW mod Rising Summer.
On this picture you can clearly see a vertical seam all the way across the middle of the unit.


Unit by Odoaker

Whats Causing This

The seam is caused by the way the light hits the surface of the mesh, and the way the normals work.

On a mesh with a single smoothing group the normals look like this:


(grey is the mesh, green the normals)

As you see The normals gradually transit into each other, making a smooth transition.

When you split the mesh on that edge, you also split the left side from the right side at that point, meaning that the normals can no longer transit into each other, resulting in a sharp edge. where if the hit hits the left side it will show a different intensity then the right side, and because there are no longer any normals in between to provide a smooth transition, you get a sharp edge.



As seen, the normals can now only come straight from the plane's surface. resulting in a sharp edge.

How can you fix this

simple, but it requires a bit of work. The best option is to not split the mesh, but unfortunately you need to do that for M2TW and RTW models, so that's not an option.

So how can we fix it? Well, you just need to make sure that the normals on both sides of the seam are in the same direction.


(seam in red)

That way the light seam disappears, and you get a smooth transition instead of the sharp seam line.
A simple cut along a straight plane will do:


(seam in green)

Thats how you get rid of those annoying seams.

[johnwhile]

Hi.
Yes this is a possible solution but in the 80% of case the objects of original models are simply "detached" where isn't necessary. Like horse, the original horse have the two side (left and right) detached but the texture or uvw-mapping are overlapping so is sufficient attach the vertices and the uvw-map.

[Maяcel]

thats only with overlapping uvw's, which wouldn't happen unless absolutely necessarily, or theres no need to have uniquely textured objects. swords for example can be overlaping, but with big things like body's this is an absolute no no.

[meliritos]

The best option is to not split the mesh, but unfortunately you need to do that for M2TW and RTW models, so that's not an option.

Stupid question here but why YOU HAVE TO split the mesh?

[Maяcel]

not stupid at all its because of the way the models are handled, if you split the model up on the uvw texture, it needs to be split up on the model too the same. This because 1 vertex cant have 2 uvw positions.

[meliritos]

i know but why split the model in the first place? Cant you map it un-split?

[stigingeoy]

Is there a updated tutorial somewhere with images?

[paleologos]

See if this may help you.