#include <gapeconsts.h>
This isn't actually a full C++ class, but simply a #define in gapeconsts.h. This can be changed from float to double (or visa versa) but because its just a #define you will have to recompile for the change to take effect. A double will give more precision, but may cause slower performance on X86 machines. (Although some other architectures, ie SGI, give better performance with doubles - then again, this isn't written for SGI boxes...) Default is a float.
Right now, it is actually defined as a "MY_FLOAT" which is a #define with the same function in the STK library. If you want to change this, you should edit MY_FLOAT in STK's "object.h" Future releases of GAPE may be less dependant on STK, and so a separate #define was created.