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Transfer Maps In Maya

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Transfer maps allow you to take one model and make another model look like that model through normal maps, displacement maps and bump maps. If you don't know what those are, you should read this tutorial on normal maps, displacement maps and bump maps. This tutorial will cover creating a normal map using the transfer maps tool in Maya.

Geometry Requirements

Unlike other features in Maya, transfer maps allow both the target mesh (this is the mesh that the transfer map will apply the normal map of the other object to) and the source mesh (this is the geometry that Maya generates the normal maps from) to have completely different geometry, different UV maps, and different polygon resolution. For this tutorial we're going to be using a high polygon torus with some deforming, and a low polygon torus. You can download the two models here. The whole point of this is to make our low polygon torus look like the high polygon torus without increasing the low polygons geometry.

Note: The high polygon torus is inside the low polygon torus so you might have to go to wire-frame mode to see it, or open the outliner. You can find a tutorial on the outliner here.

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Setting Up The Transfer

First select trans_torus1 and on the rendering menu set go to lighting/shading>transfer maps... This will open the transfer maps window.

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Target mesh

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Since you selected the low poly torus, it will automatically become the target mesh. You can have multiple target meshes. If you didn't select the mesh when you first opened the transfer maps editor, you can load it by selecting it and, in the transfer maps editor, clicking Add Selected. If you want to remove a target mesh, select it and go to Remove Selected. Make sure the output UV set is set to the current UV set for the model. If you're using the example file, that won't be a problem.

Source Mesh

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Go down to the source mesh tag and open it. By default its set to All Other Meshes (geometry). This doesn't work if you have other items in the scene that you don't want to be used as a source mesh. To fix this, select the source mesh, in our case its trans_torus2, and click Add Selected. Now, only that object is a source mesh. If you wanted to have every object but the selected object a source mesh, click Add Unselected. To remove a source mesh, select it and hit Remove Selected. You can right click on an object in this list and select it or remove it from the list.

Output Map

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One transfer map can output more than one type of map. By default its set to normals map. It can create normal, displacement, diffuser, shaded, alpha, ambient (ambient occlusion - I've written a tutorial on ambiance occlusionhere), and custom (you can use a custom shader to be used as a transfer map).

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Transfer maps can create more than one map at a time. Even though we're only using normals maps, click on the displacement map icon. It will add displacement map options for the output section.

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To remove the displacement map option, click Remove Map. Now what's left is the normal map's options that are created by default. You can set the location of the map file on your hard drive by using the file format (avoid using Jpeg) the option to include ore not include materials. The map space (leave it at Tangent space) and the option to use common (global) Maya settings. If you were to uncheck this, you could change the maps width and height in pixels for this normals map.

Connect output map

Connect maps to shader - This will allow Maya to automatically set up connections to the map files to the targets meshes shader.

Connect maps to - New shader - This will create a new shader for the model, and the other will use the existing shader on the model.

Maya common output

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Map width/ height - This attribute sets the width and height in pixels of the texture map. The option to keep the aspect ratio is best left on. The higher the resolution of the map, the more detail we'll be able to transfer. But it will take longer for the transfer map to be created and it will take longer for the transfer map to render.

Transfer in - world space - All maps will be created in relation to world space (recommended).

Transfer in - object space - All maps will be created in relation to an objects positioning.

Transfer in - UV space - All maps will be created to both objects' UVs (not recommended).

Sampling quality - The lowest option is best for use for quick previews. The high setting is great, but takes very long for the map to be created.

Filter size - Sets the filter size for the map.

Filter type - You have 3 options: Gaussian, triangular, and box. If you don't know what filters do, read this tutorial.

fill texture seems - Adds additional pixels around each UV shell. This prevents filtered UV borders from showing up.

Ignore mirrored faces - When checked, UVs that have been reversed will not be included in the transfer map.

Now that we've got that all explained, hit Bake and Close in the transfer map window. It may take a while before it finishes creating a texture map.

Now, select trans_torus2 and delete it. Open the render settings window by going to window>rendering editors>render settings. Set the render using to Mental Ray. The reason we need to do this is because, as noted in my tutorial on normal maps, Maya software can't render them. Now hit render. The low poly torus now looks like the high poly torus. This is all because of the normal map.

This is part one of a 2 part series. Part two will cover how to use these techniques for making a low poly game model.

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