81 Influence of creases Like all T splines and NURBS control points creased control points influence the surface within a two face region This means if only one edge is creased the next two edges in the loop will be partially creased and the third edge away in the loop will not be creased at all Influence of creases a Edge to be creasedb After crease c Enlarged image of b with Zebra stripes How the crease blends into the surface 1 Creased edge 2 exit the command Now the extrusion is balanced Extruding with symmetry To extrude across a symmetry boun dary select faces on both sides of the symmetry border If just one face is selected separate extrusions will be made on each side of the symmetry border Extruding across symmetry 86 Extrude edge Extruding edges allows you to add more geometry on the borders of your model To use this command select an edge or edges to be extruded and run the tsExtrude command Extruding edges is only permitted on the edge of the surface Select entire borderRun tsExtrudeMove the edges Single edges can be extruded or an entire border can be extruded Select edge or edges to extrude Run tsExtrude Move the edge TipExtruding edges to smooth T splines borders If the edge of your T spline model has a crease this is how to fix it This is a very important tip that will greatly improve your modeling T spline surfaceTwo edges extruded Notice that the surface has creases this is because the border contains a sharp inner corner which pushes a crease to the rest of the surface through the isocurves One way to make this creased surface smooth is adding a complete border loop Select all border edges above Extrude the border edges Notice that the topology of the border changes and all border points now have a valence 3 which is the best for smooth contours 87 Extrude curve In T Splines 2 2 curves can be extruded Just select the curve and run the tsExtrude com mand Tip Extruding with the manipulator Instead of clicking the Extrude icon just select your object curve face or edge hold down the ALT key and drag the manipulator to make an extrusion This works with the translate rotate and scale manipulators 88 Thicken The tsThicken command is a quick way to approximately shell or give thickness to a surface Before Thickened smooth borders tsThicken does not give exact shelling instead it creates an edi table solid with minimal control points For exact shelling use the Rhino OffsetSrf command which is accurate to within the file tolerance 89 Thickening open surfaces The thicken command will take a sur face and thicken it by duplicating the surface and connecting the two surfaces around the edges The user can specify the thickness by either entering a number into the command prompt or moving the mouse and clicking The thickness is measured according to the surface normal for each control point Open T spline surfaceThickened 3 units uncreased edgesThickened 3 units creased edges The DirectionType option allows you to thicken Normal to the surfa ce or normal to each vertex PerVertexNormal T spline surfaceThicken Normal Thicken PerVertexNormal Options The CreaseEdges option allows for creased or smoothed edges on the thickened surface Thickening closed surfaces If the surface is closed the Thicken command creates a second separate surface The T spline is thickened again yielding the red surface With clipping plane to show both surfaces Creating self intersecting surfaces with Thicken tsThicken does not check to see if it creates a self intersecting object in fact if the inputted thickness is greater than the minimum curvature of the object the model will self intersect We recommend visually exami ning your model for self intersections after thickening it Self inter sections can be resolved by manually moving control points 90 Duplicate faces tsDuplicateFaces makes a copy of T spline faces This will copy the locations of the control points If you are in box mode it will look like an exact copy but if you are in smoo th mode if you are copying an open selection the border edges of the selection may have different curvature from the original surface Select faces to duplicateA new surface will be created 91 Deleting detail surface Delete The Delete command lets you remove faces edges and vertices from your model Deleting faces will delete the surface Deleting faces is an alternative to trimming and leaves an editable model Deleting edges and vertices from a model will produce changes of curvature Deleting edges removes them from the surface This is similar to Rhino s RemoveKnot command except that partial edges can be deleted as well Deleting a vertex will also remove any edges touching the vertex 92 TipUse the Delete key on your keyboard instead of clicking the icon for deletions Deleting faces vs trimming Deleting faces is a new concept for traditional NURBS modelers This is an alternative to trimming the surface Unlike trimming though deleting a face will actually remo ve it from the surface and leaves definit