From submesh : this check box let user have the ability to select closed lines to define submesh on the selected mesh. If this check box is check, the Create button will be enabled, the Trim button will be disabled because surface from sub mesh will be trimmed in default;
Create: after you checked the from submesh button, this button will be enabled. Click this button, select some lines to make closed loop, then click right-mouse button, a new surface with the specified tolerance will appear. If you would like to adjust the tolerance of the surface, reset Max Tol and click Apply button, the surface will update.
Shape: topology shape of your mesh model. If your mesh model is like plane, choose plane-homeomorphous; if your mesh model is like cylinder, choose cylinder-homeomorphous;if your mesh model is like semisphere, choose semisphere-homeomorphous.
Set control number: this check box let user have the ability to set an initial control point number for the surface. Such as u = 43, v = 23. This check box is only designed for those users who would like to control the surface in advanced way. Sometimes, if user type a reasonable control point number, it will be helpful to increase the speed. Generally, however, user does not need to care this control number, the program will calculate a suitable number automatically.
Max Tol: the maximum deviation between surface and mesh.
Smooth: the smooth controller of the surface.
Trim: to trim or untrim the generated surface with the boundary line of the mesh.
Apply: user clicks this button to generate surface. After a surface is generated, if the tolerance is not desired, continue to click this button to get a surface with a desired tolerance.
Error analysis: check this button to analyze the deviation error between mesh and surface.