What does an esri projection file represent?

Question

I have managed to really confuse myself here. I am trying to determine what the associated *.prj file that accompanies an esri shapefile means. If I have a *.prj file that has this in it:

PROJCS["WGS 84 / World Mercator",
    GEOGCS["WGS 84",
        DATUM["WGS_1984",
            SPHEROID["WGS 84",6378137,298.257223563,
                AUTHORITY["EPSG","7030"]
            ],
            AUTHORITY["EPSG","6326"]
        ],
        PRIMEM["Greenwich",0,
            AUTHORITY["EPSG","8901"]
        ],
        UNIT["degree",0.0174532925199433,
            AUTHORITY["EPSG","9122"]
        ],
        AUTHORITY["EPSG","4326"]
    ],
    PROJECTION["Mercator_1SP"],
    PARAMETER["central_meridian",0],
    PARAMETER["scale_factor",1],
    PARAMETER["false_easting",0],
    PARAMETER["false_northing",0],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]
    ],
    AXIS["Easting",EAST],
    AXIS["Northing",NORTH],
    AUTHORITY["EPSG","3395"]
]

Two things are being defined in here. The projected coordinate system and the geographic coordinate system.

1. Does this mean that the coordinates in the shapefile have already been calculated and if you wish to go back to the geographic coordinates you need to use the above projection variables to do the transformation or is it a meta data value indicating the current transformed coordinate values?

I want to draw the shapefile using OpenGL so do I need to do a trasformation based on the projection information or do I just use the coordinates as read from the shapefile?

Answer 1

Looking at this answer: https://gis.stackexchange.com/a/2386

It appears that the prj file represents the current projection. So each coordinate in the shapefile is already in the denoted coordinate system...