Get specific parameter in CRS information with Python gdal

Question

I have a tif image containing its CRS. I would like to extract the parameter "central_meridian". I have the following piece of code:

from osgeo import gdal,osr
ds=gdal.Open(r'hrs0000bf5c_07_if177l_trr3_CAT_scale_trial_p.img.tif')
prj=ds.GetProjection()
print prj

srs=osr.SpatialReference(wkt=prj)
print srs.GetAttrValue('PARAMETER',0)
print srs.GetAttrValue('PARAMETER',1)

The output I get is the following:

    PROJCS["Mars_Npolar_Stereo",GEOGCS["GCS_Unknown",DATUM["Unknown",SPHEROID["S_Unknown",3396190,169.8944472236118]],PRIMEM["Greenwich",0],UNIT["degree",0.0174532925199433]],PROJECTION["Polar_Stereographic"],PARAMETER["latitude_of_origin",90],PARAMETER["central_meridian",160.0712280273438],PARAMETER["scale_factor",1],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]]]

latitude_of_origin
90

I would like to fetch the second parameter "central_meridian" but i don't know how to do it? Any ideas?

##EDIT

If trying to open a list of files given by a list like:

from osgeo import gdal,osr from gdalconst import GA_ReadOnly

f = open('list.txt')
for line in iter(f):
    print line
    ds=gdal.Open(line,GA_ReadOnly)
    prj=ds.GetProjection()
    srs=osr.SpatialReference(wkt=prj)
    print line + " " + srs.GetProjParm( osr.SRS_PP_CENTRAL_MERIDIAN)
f.close()

I get the following error: ERROR 4: `frt0000703c_07_if187l_trr3_CAT_scale_trial_p.img.tif ' does not exist in the file system, and is not recognised as a supported dataset name.

I tried different ways to do it and went through documentation but no luck. Any ideas why it does not recognizes it as a filename?

Answer 1

You could use the OGRSpatialReference::GetProjParm to obtain the central meridian value as described in the GDAL tutorial for Querying Coordinate System:

srs.GetProjParm( osr.SRS_PP_CENTRAL_MERIDIAN)

---

So you could use:

from osgeo import gdal,osr
ds = gdal.Open(r'hrs0000bf5c_07_if177l_trr3_CAT_scale_trial_p.img.tif')
prj = ds.GetProjection()

srs = osr.SpatialReference(wkt=prj)
srs.GetProjParm( osr.SRS_PP_CENTRAL_MERIDIAN)