What interface/class or interfaces/classes are used to represent the definition of a CRS in the library?
What interface/class or interaces/classes are used to perform the actual coordinate transformation? What objects or primitive types do the methods of the transformer accept as input? How are the source and destination CRS designated to the transformer?
How are standard CRS definitions obtained? Is this from a copy of the EPSG database, from Proj4 definitions, from WKT defintions, or from another source? Is it from multiple sources?
How easy is it for users to define a new CRS?
Is there a single interface/class that can be used to represent a transformation algorithm?
Are there utility classes to work with spheroids and latitude/longitude values?
How are the transformations allowed by the library tested?