If you're not handy in generating decal maps for your models, 3DPainter can do this automatically for you using a tiled based approach. This means that 3DPainter will assign to each patch a tile on the texture. Around each tile, a margin of a few pixels is added that allows the tiles to blend with each other on the model. Patches that are neighbours on the model are not necessary neighbours on the texture. Therefore, painting objects decal mapped this way should be done in projection paint mode.