You may change the default values but most of the time this is not necessary. Press OK to make the cover.

MaxSpans

This option controls the maximum number of control vertices on the resulting cover surface.

Flattening Factor

This controls the flattening of the middle of the cover surface. A larger value will produce more flattening. This value goes from 0 to 10.

Position tolerance

This controls the boundaries position tolerance. It is the maximum value allowed by the cover algorithm and most of the time the resulting error will much smaller than the maximum value specified.

Tangent tolerance

This controls the boundaries tangent tolerance for the boundaries that were selected as tangent. It is the maximum value allowed by the cover algorithm and most of the time the resulting error will much smaller than the maximum value specified.

Simplify

This option allows the user to specify if they would like the resulting cover surface to be simplified to an analytic surface type. This option is good for planar covers.