Issue with gdal getprojection and setprojection returning different information

Question

I am using Landsat imagery from the USGS. Those who use them may know that the projection attribute is wrong (everything is in the Northern hemisphere). I have a script to process tar.gz files and output a stacklayer with selected bands of interest. I deal with the projection error by modifying the EPSG value and writing a new projection like this:

orgeoproj =  dst.GetProjection() # North projection
osn = osr.SpatialReference()
osn.ImportFromWkt(dst.GetProjection())
nEPSG= int(osn.GetAttrValue("AUTHORITY",1))
sEPSG= nEPSG + 100
print "mudando EPSG Norte a Sur"
osn.SetFromUserInput("EPSG:%d"%sEPSG)
modgeoproj = osn.ExportToWkt()

When I print orgeoproj (original geoproject), the output has Authority values like:

PROJCS["WGS 84 / UTM zone 23N",GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433],AUTHORITY["EPSG","4326"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",-45],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AUTHORITY["EPSG","32623"]]

After modifying the EPSG value, the modgeoproj is OK now and showing the right EPSG value for the southern hemisphere! The problem rises when I write the modgeoproj with SetProjection(modgeoproj) to the stacklayer and then load it with another script.

After a GetProjection(), I only get:

PROJCS["WGS_1984_UTM_Zone_23S",GEOGCS["GCS_WGS_1984",DATUM["WGS_1984",SPHEROID["WGS_84",6378137,298.257223563]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",-45],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",10000000],UNIT["Meter",1]]

There's no Authority Information and I need it! What can possibly be wrong?

Answer 1

I'm not sure if Geotif format stores the EPSG code, or the whole projection definition in WKT or proj. If you compare the wo definitions:

D:\Karten\gdal\gdal-1-11>gdalsrsinfo EPSG:32623

PROJ.4 : '+proj=utm +zone=23 +datum=WGS84 +units=m +no_defs '

OGC WKT :
PROJCS["WGS 84 / UTM zone 23N",
    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["Transverse_Mercator"],
    PARAMETER["latitude_of_origin",0],
    PARAMETER["central_meridian",-45],
    PARAMETER["scale_factor",0.9996],
    PARAMETER["false_easting",500000],
    PARAMETER["false_northing",0],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]],
    AXIS["Easting",EAST],
    AXIS["Northing",NORTH],
    AUTHORITY["EPSG","32623"]]


D:\Karten\gdal\gdal-1-11>gdalsrsinfo EPSG:32723

PROJ.4 : '+proj=utm +zone=23 +south +datum=WGS84 +units=m +no_defs '

OGC WKT :
PROJCS["WGS 84 / UTM zone 23S",
    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["Transverse_Mercator"],
    PARAMETER["latitude_of_origin",0],
    PARAMETER["central_meridian",-45],
    PARAMETER["scale_factor",0.9996],
    PARAMETER["false_easting",500000],
    PARAMETER["false_northing",10000000],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]],
    AXIS["Easting",EAST],
    AXIS["Northing",NORTH],
    AUTHORITY["EPSG","32723"]]

you see that the UTM 23S has a different false_northing value. So you may have to alter that value too.