> What exactly is the purpose of default sets for RealTypes?
These default Sets are used as the domain Sets of Fields
when the RealType (or RealTupleType) are the domain Type
of the Field and no domain Set is explicitly provided.
In practice this is never used (and shouldn't be). Its in
the system because it was important in the old C language
version of VisAD (version 1.1). The Java version (2.0) is
greatly improved, and because of those improvements default
Sets are not necessary or even useful. However, I didn't
foresee that during the design of the Java version, so
these default Sets are with us like other prehistoric beasts.