To Edge

It is also possible to constrain a SubD edge to edges in the reference geometry.  If there is a single periodic edge, such as would be produced by a cylinder, it is not important where the vertices of the SubD fall.  However, if there are multiple edges, such as in the example below, it is important to align SubD vertices with reference surface vertices.  It is a good workflow to utilize either Cage mode or Control mode while getting the model ready for edge constraints.  The control edges need to align properly with the constraint geometry.  If this doesn’t happen, you may need to remove the constraints and try again after moving things closer to the corresponding reference geometry.  

The first image below shows a Power Surface after edge loops have been inserted to align the vertices on the bottom open edges with existing reference vertices.  The second image shows moving the open edges into position close to their intended mates.  The third image shows the result of the To Edge command applied to the entire loop of edges.

The bottom row of images shows the resulting SubD display and the resulting Solidworks body.  Note that To Edges is often used when there is a surface with open edges in the Solidworks body or surface.  The last image shows some examples of edge constraints.  

The following sequence of images shows what happens if the SubD vertices don’t match with the reference geometry vertices and the process used to fix the issue.  The Insert Loop and

Draw Edges commands come in handy in cases like this.

The image below shows a case where one subD edge covers too much shape change on the reference geometry.  You can see the folding in the middle of the first image below.  There are two ways to adjust the model to solve this problem.  The first way is to insert an additional loop, as shown in the second image.  The other way is to adjust the existing loops by moving them closer to the problem area.  The advantage of the second technique is that it doesn't require additional geometry in the SubD.  A general rule of thumb is that one edge of a SubD should not

cover more than 90 degrees of curvature in the reference edge.

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