Rebuilding Curves

I found it crucial to have curves rebuilt before creating a new surface from them. One aim I know of for rebuilding a curve is to make the curve into a single span curve. As stated in Rhino 5's training manual level 2, although it is not necessary to get high quality surfaces by doing this, it produces predictable results.

In this example found on page 99 of the level 2 training manual, first on each endpoint of a curve, a tangent line is drawn by using Line command with Extension option. Each of the 2 lines maintains the tangency direction of an original curve from each end point and coming back towards the curve.

Then use the Rebuild command (Edit menu: Rebuild) to rebuild the curve. In the Rebuild Curve dialog, change the Degree to 5 and the Point Count to 6 points. Uncheck Delete input, check Create new object on current layer. It is better practice that the original curves are kept in a separate layer. Click the Preview button. Note how much the curves deviate from the originals.Although there is a Rebuild option in many commands such as Loft, rebuilding the curves before lofting them gives you control over the degree of the curves as well as the number of control points.

Lock the Original Curves (in a separate layer if you can). We need to see these curves but we do not want to be able to select them. Select one of the rebuilt curves, and turn on the Control points and Curvature graph.

Fair the curve by adjusting points until it matches the original curve closely enough. Start by moving the second control point from each end of the rebuilt curve onto the tangent line. Use the Near object snap to drag along the tangent line.

 

 

 

Check the curvature graph to make sure the curve has smooth transitions. The curves are fair when the points are adjusted so the rebuilt curves match the original locked curves closely, with good graphs.