模闆：如果不明白，先空着也行，如下所示：
檔案：就是你要在哪個模型上進行繪制貼圖
https://docs.substance3d.com/spdoc/udim-144310352.html
what are UDIMs?
UDIM was invented by richard addison-wood and came from wetal digial (circa 2002). the term UDIM comes from U-Dimension and design UV ranges. the uv range 0-1 being 1001, the range 1-2 being 1002, and so on. we designate 指定 by UDIM tile a specific range, the tile 1001 being the range 0-1 of a given mesh. the goal of having multiple uv ranges it to increase the texture resolution of a given mesh. instead of working with very big textures (16k, or even 32k) which are hard to optimize it is instead better to split a mesh into sub-parts. because of the UDIM convention, parsing files is easy as the ID of a tile is embedded into the filename, which make them convenient to use in external rendering software such as Vray or Arnold.
more reading:https://www.fxguide.com/fxfeatured/udim-uv-mapping/
法線貼圖格式：
unity-》選用opengl，ue4-》選用dx
maya->opengl， max-》dx
貼圖的分辨率：