The main idea of Natural terrain is based on height-fields. MGS computes a rectangular grid of Z values, and builds a triangle mesh out of it. You have several ways of interacting with the height field. MGS can spawn an external process, gforge.exe to produce a random grid. You can also provide MGS with some boundary points, designing the global shape of the mesh.

When the mesh is done, MGS can spawn QSlim.exe, which will optimize the mesh, and reduce the face count.

Let's start by creating a rectangular brush, of about (512,384) size in XY, and about 190 height. When you ask ground feature from the MGS menu, you will get a preset dialog box, just hit OK and you will get something like that :

If the decimate percentage is 0, you will always get a regular grid. The meshsize parameter can be used to change the size of the grid. Now try the same thing with a 60% decimation. The noise level is a parameter between 0 and 4, from smooth noise to very twisted. You will get a triangle mesh with 60 percent of removed faces.

You can also provide some boundary conditions, for example if you want to have more control over the shape of the mesh. Call the ground dialog box without any selected brush. First enter a boundary line, MGS will compute a rectangular grid along the axis with all the points you have provided.

Now enter a fixed point inside the grid, in the middle, with a higher Z value. MGS will compute a grid to fit these conditions.

You can enter several boundary lines, each will be a polygon line. But you can only have one fixed points entry. MGS will not draw fixed lines between fixed points.