Cleaning a curve before creating a lofted surface

In the following example, some of the curves to be used in the creation of a lofted surface have invisible sharp points. Because of those points, the quality of the resulting surface might be lower than expected.

As you will see, as soon as a curve containing an invisible sharp point is selected, an appropriate message is displayed. By selecting the Clean Curves or Curvilinear options in the Parameterization drop-down list under More Options - Surface Type Options, you can create a nicer surface. In fact the command will not use the original curve — which will not be changed — , but a local copy with no sharp points (thanks to a different parameterization).

Once you have started the Grid Lofted Surface command, you can proceed as described in the following steps (please note that you can follow this step-by-step example by loading file: "CleanCurves.e3").

1	In the Select As drop-down list, select the Grid option.
2	Select the curves of Boundary Set A as in the following illustration and end selection:
3	As the second set of curves select the four curves as in the following illustration: The Show warnings button ( ) shows up on top of the selection list. Click it to display the warnings. As you can see, the command detects invisible sharp points, highlighted using a marker, and an appropriate warning is displayed. Once you selected all the curves of the second set, end selection. The preview of the resulting surface is the following: Using the appropriate Parameterization options you can get a better result: Intrinsic The ordinary curve parameterization. Though this type of parameterization can be used in most of the ordinary situations, you might need to use another one in order to get a smoother surface. For example, sharp points, if any, are not detected when using the intrinsic parameterization. Clean curves When some of the curves to be used in the creation of a lofted surface have invisible sharp points, the quality of the resulting surface might be lower than expected. As soon as a curve containing an invisible sharp point is selected, an appropriate message is displayed. By selecting this item, you can create a nicer surface. The command will not use the original curve, which will not be changed, but a local copy with no sharp points (thanks to a different parameterization). Curvilinear A normalized arc length parameterization type (which is: the curve parameter varies proportionally to the curve arc length, so that arcs with equal length on the curve correspond to equal variations of the curve parameter). Using this option all the input curves are internally re-parameterized based on their arc length and you will generally get surfaces with more regular isoparametric curves. Please note that if the selected curves have invisible sharp points, using this option will also result in creating nicer surfaces as in the case of the Clean curves option. Now, if you select the Clean Curves option, the preview changes to the following:

And here are the three surfaces you can obtain by selecting the three parameterization options:

Intrinsic	Clean Curves	Curvilinear

As you can see, by selecting Clean Curves or Curvilinear the creases of the surface displayed in the first illustration disappear and the resulting surface is nicer and smoother.