It resets 4D and 3D matrices and 3D light direction, and it stops momentum. It resets 3D rotation and translation matrices, and it stops momentum. To understand the basic philosophy of the rolling ball interface, start with a 3D object such as square.3mesh. Now load a solid 3D object like sphere.3mesh or torus.3mesh. The default mode, in which all 4D rolling ball motions are referred to the screen-based xyz coordinate system with z out of the screen, is the most natural one to emulate a 3D mouse.
Analogous behavior occurs for y motions and for shift-middle x and y mouse motions.
Turn on the drawing of xyzw axes to see the different effects. If not present, vertices are 3D and MeshView automatically set 0.0 to the w component. 4 and N cannot both be present. And key characters are case insensitive except MESH should be capitalized. This format is a natural choice for parametric surfaces and runs faster than off file format.