Isoparametric curves are lines running along the surface in the U and V directions, showing the shape of the surface as defined by the CVs.
Alias draws a NURBS surface as a mesh of curves, called isoparametric curves, running in the U and V directions.
Isoparametric curves are sometimes called isoparms.
Unfortunately, the term “isoparametric curve” is used to describe two related but subtly different features of a surface:
A line of constant parameter at an edit point. The isoparametric curves at edit points are special, since they represent the boundaries between “patches”. Like CVs, these isoparametric curves are important in representing the surface within the system.
Alias draws these types of isoparametric curves using solid lines.
Any line of constant parameter in either U or V. For example, if you join together every point on the surface where U=1.5, the resulting line is a U isoparametric curve:
Alias draws these types of isoparametric curves using dotted lines.