I have a DEM with cell size 100,100 with geographic coordinate system GRS_1980_Transverse_Mercator, Datum: D_GRS_1980. I created some extra shapefiles with projected coordinate system: Greek_grid, projection: Transverse_Mercator and geographic coordinate system: GCS_GGRS_1987 and datum:D_GGRS_1987. Adding them in ArcMap I have the message that my layers use different spatial reference which is reasonable because the shapefile datum was different from the DEM I am using. I checked online and found in http://edndoc.esri.com/arcims/9.2/elements/gcs.htm the geographic coordinate systems I am using. They are the 4121 and 4019. They look to have the same characteristics. Does anyone know why they exist with different names? Or am I missing something?
4121 GCS_GGRS_1987 GEOGCS["GCS_GGRS_1987",DATUM["D_GGRS_1987",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]] 4019 GCS_GRS_1980 GEOGCS["GCS_GRS_1980",DATUM["D_GRS_1980",SPHEROID["GRS_1980",6378137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]]
Thanks in advance, chch