Part II: Building Intelligence into Your Parts
Isoparameter U-V lines ..................................................................................
The mesh or grid shown in the previous images appears automatically for certain types of features,
including lofts. The grid represents isoparameter lines, also known as NURBS mesh or U-V lines.
This mesh shows the underlying structure of the faces being created by the feature. If the mesh is
highly distorted and appears to overlap in places, then it is likely that the feature will fail.You can show or hide the mesh through the right mouse button (RMB) menu when editing or cre-
ating a Loft feature, unless the SelectionManager is active. In this case, you can see only
SelectionManager commands in the RMB menu. In addition, planar faces do not mesh, only faces
with some curvature.Guide curves .................................................................................................
Guide curves help to constrain the outline of a loft between loft profiles. Although it is best to try
to achieve the shape you want by using appropriately shaped and placed loft profiles, this is not
always possible. The most appropriate use of guide curves for solid lofts is at places where the loft
is going to create a hard edge, which is usually at the corners of loft profile sketches. Guide curves
often (but not always) break up what would otherwise be a smooth surface, and you should avoid
them in these situations, if possible.Best Practice
Do not try to push the shape of the loft too extremely with guide curves. Use guide curves mainly for tweaking
and fine-tuning rather than coarse adjustments. Use loft sections and end constraints to get most of the overall
shape correct. Pushing too hard with a guide curve can cause the shape to kink unnaturally.n
Although guide curves can be longer than the loft, they can not be shorter. The guide curve applies
to the entire loft. If you need to apply the guide curve only to a portion of the loft, then split the
loft into two lofts: one that uses the guide curve and one that does not. The guide curve must
intersect all profiles in a loft.If you have more than one guide curve, the order in which they are listed in the box is important.
The first guide curve helps to position the intermediate profiles of the loft. It may be difficult to
visualize the effects of guide-curve order before it happens, but remember that it does make a dif-
ference, and depending on the difference between the curves, the difference may or may not be
subtle.Guide curves are also used in sweeps, which I address later in this chapter. Figure 7.12 shows a
model that is lofted using guide curves. The image to the left shows the sketches that are used to
make the part. There are two sketches with points; you can use points as loft profiles. The image in
the middle shows the Loft feature without guide curves, and the one to the right is the part with
guide curves. If you would like to examine how this part is built, you can find it on the CD-ROM
with the filename Chapter 7 Guide Curves.sldprt.