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I have this problem accessing to the coordinate reference system(crs) of a raster layer map. I wonder if such thing is possible? I have used this xml from GDAL open map service to load in a raster layer(crs id 900913) to my stand-alone pyqgis application (http://www.gdal.org/frmt_wms_googlemaps_tms.xml) It displays the map just fine, but when I tried to draw an icon at a specific lat long position (crs id 4326), the icon appeared weirdly. I used the QgsCoordinateTransform class to convert the coordinates. Please advise me what I should do to get it right? I am very new to pyqgis. Thanks a ton!

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1 Answer 1

I am not entirely sure if i understood your question right, but you flagged it with pyqgis and it is quite simple to get the CRS here.

#Assume that you have a raster layer of type QgsRasterLayer
crs = rasterlayer.crs()
print crs.toProj4()
# You can extract CRS of multiple layers and simply compare them with ==
crs1 == crs2 # Returns false, if the CRS is differnet

Using gdal it would look similar to this

rasterPath = "your file" #load as a gdal image 
srcImage = gdal.Open(str(rasterPath))
srcImage.GetProjection() # Returns a string, which contains the crs. The string can be processed by python string splitting or by turning it into a list
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Thank you so much. That's exactly what I want. However my problem is not yet solved. I want to draw an icon at a specific (lat, long) onto a raster layer which I loaded from this xml file (gdal.org/frmt_wms_googlemaps_tms.xml). The raster layer is using EPSG:900913, so I converted my lat long position using QgsCoordinateTransform(4326->900913). The icon however appears way off the position i intended to draw. It seems like the origin of destination crs is not set properly. Anyone knows this problem? –  Justin Apr 12 '13 at 3:39

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