UVs
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The most common method of creating a UV map is the automatic method. But this method creates a lot of unnecessary seams and improperly placed UV islands, which will create visible seams and texture mismatch when textures are applied.
Texel is an important part of creating a UV map. If you don't maintain the texel size, the textures will look inconsistent.
The wall with the window has a texel of 5.12px/cm by 1024px texture, and the wall with the doorway has a texel of 10.24px/cm by 1024px. As a result, the brick size is very different.
The texel standard for a tiled texture is 1024px per px texture size. 1024px should equal 1m.
Example
The brick tile size in the example is 2048x2048px, so for the tile size to be correct, you need to set the texel to 1024px per 2048 (2m) texture.
In this case, the size of the tile can be checked by looking at the size of the real brick and, having made a box of the appropriate size, attaching it to the tile.
Lightmap - UV map, which is needed to bake the light in the scene. It has a positive effect on the performance and gives more realistic shadows, as distinct from dynamic shadows.
For Lightmap it is necessary to create an additional UV channel, because there may be several of them on the model - Tile, Detail, etc.
Lightmap should always be the last channel.
The main requirements for the UV lightmap:
UV Islands must not go beyond zero Udim, as is acceptable for a tile.
Texel is not critical, but the larger it is, the better the quality of the bake.
Make a large distance between UV islands. Otherwise, the light information may end up on a nearby UV island.
In the left example, the UV islands are not clearly indented. As a result, there is a glare in the corner.
In the right example, there is no glare in the corner. When baked, the light is applied to the texture like a spray. If the overlapping radius touches the nearby island, you get such artifacts.
Detail UV can display a lot of different information on itself: unique normals, AO, tile texture blending masks
Detail UV has the following requirements:
UV islands must be in Udim 0 and not overlap its boundaries;
Exclude random intersections of islands (overlaps are allowed if they are needed);
Better to keep the distance between the islands at least 3px.
