We use shape files for data exchange. I've looked at the .prj files: different programs produce different prj files.
Is there a standard how the parameters must be specified in a prj file?
AFAIK the name of the projection (e.g. PROJCS["ETRS89 / UTM zone 32N (zE-N)",…]) can be freely assigned. But I can not believe that the name of the datum (e.g. DATUM["D_ETRS_1989",…]) can be assigned freely too.
I have found no information about this. Even in ESRI Shapefile Technical Description there is no information about .prj files. The ESRI KB Article 14056 HowTo: Create projection metadata (.prj) files for shapefiles says: “You have to use the predefined names for map projection and parameter objects”. But the article does not specify where to find these predefine names. Does each GIS-company specify it own names? Or does EPSG specify these names?
Here are a few differences in a section of .prj files (EPSG 4647) between QGIS, AutoCAD Map and spatialreference.org