“Sharp” is a designation that prevents a patch line or point from being smoothed during NURBS surfacing.
Grids > Specify Sharp Contours (available after Grids > Construct Grids and before NURBS > Fit Surfaces) designates patch lines and/or patch-line intersections as sharp so that NURBS > Fit Surfaces does not remove detail such as abrupt edges and creases. A contour turns purple when it is designated as sharp.
This function allows sharp lines and points to be selected manually or calculated automatically.
Contours radio button - use the mouse to designate individual patch lines as sharp contours.
Points radio button - use the mouse to designate individual patch-line intersections as sharp (such as the top of a cone).
Add All Contour Lines button - designates all patch lines as sharp lines.
Constrained button - designates all
Unextended button - designates all unextended (orange) contour lines as sharp.
OK button - saves the designations to the object and closes the dialog.
Cancel button - terminates the function without designating sharp lines or points.
To view the sharp lines and points, check the Sharp Lines checkbox in the Primitives Manager.
Also see Grids > Clear All.