[postgis-users] Spatial reference systems

[Luis Mota]

Hi everyone, can anyone help me with spatial reference systems? Nothing 
theoretical, it's just a question of nomenclature...

I am working with geographical data from Lisbon in Portugal. I imported 
some data from a shape-file, but I had no information (at least that's 
what I think) about the underlying reference system. Because of this, I 
started looking at the spatial_ref_system table to find the appropriate 
SRID.

I noticed, however, that there were differences between the definition 
found at OpenGIS and the definition in the PostGIStable ... Please look 
at it:

 From the spatial_ref_system table:
 20790 | EPSG      |     20790 | 
PROJCS["Portuguese_National_Grid",GEOGCS["GCS_Lisbon_Lisbon",DATUM["D_Lisbon",SPHEROID["International_1924",6378388,297]],PRIMEM["Lisbon",-9.131906111111112],UNIT["Degree",0.017453292519943295]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",200000],PARAMETER["False_Northing",300000],PARAMETER["Central_Meridian",1],PARAMETER["Scale_Factor",1],PARAMETER["Latitude_Of_Origin",39.66666666666666],UNIT["Meter",1]]

 From http://www.opengis.org/techno/interop/EPSG2WKT.TXT:

EPSG=20790
PROJCS["Lisbon (Lisbon)/Portuguese National Grid",GEOGCS["Lisbon (Lisbon)",DATUM["Lisbon",SPHEROID["International 1924",6378388,297]],PRIMEM["Lisbon",-9.13190611111111],UNIT["degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",39.6666666666667],PARAMETER["central_meridian",1],PARAMETER["scale_factor",1],PARAMETER["false_easting",200000],PARAMETER["false_northing",300000],UNIT["metre",1]]

As you can see, the names of  spheroids, data and projections are 
different...

This doesn't seem to be too bad since the numerical data is identical, 
but to me this is a problem: I need some kind of sure nomenclature in 
order to refer to reference systems...

What should I use for this? Is there any standard? Should I use this 
EPSG number? What about the other ref-systems whose auth_name is ESRI? 
They are, at least some of them, different from the ones from EPSG...

Any comments on this?

Best regards, Luís Mota