Take a look at a new HDA called Mesh Tiler created by Paul Ambrosiussen that takes a collection of meshes distributed on a planar surface (not just square) and makes it tileable. The result will let you copy the new “tile”, without getting any obvious seams. The tool is said to be useful for baking down a tile you scatter a set of high-resolution meshes on. The HDA will give you control over a couple of parameters to get a desired result.
The Mesh Tiler has two main “modes” you can choose between. The Tile Mode parameter allows the user to choose between “Full Tile” and “Piece Tile”. Full tile should be used when using the tool output for baking it to texture, since it generates a fully seamless setup for a orthographic top-down bake. Piece Tile should however be used when planning on tiling the mesh itself. This ensures you will not have duplicate geometry on borders when aligning multiple pieces. (Think of it as a puzzle piece)
The tool also offers the possibility to quickly debug the result of the “tiling”. It will generate 9 HeightFields, on which the tiling geometry will be projected. This will then reveal any seams / obvious patterns in your setup. The user can also enable “Color Tile Meshes”, which will color the meshes that have been adjusted for the tile red. This helps tweaking the “Tile Edge Density” parameter, which can make the density of the borders equal to the center. (Making meshes seamless often increases the density of meshes on the border).
Baking to Texture
Once you have a tiling mesh you like, plug the result into the simple baker tool. (and your planar surface) Then select which texture maps you want to extract, such as Normal Map, Height Map, Roughness, AO, etc. Set your baking resolution and hit render. For more information on how to set up the Simple Baker, follow its tutorial here.
You can find more details on the tool and get it here.