QGIS python - 获取栅格单位

Question

In QGIS with pyQgis I would like to determine if input raster has units in degrees or metres. Here I learned I can get projection from raster using GDAL:

inRaster = gdal.Open(rasterInPath,GA_ReadOnly)
projRef = inRaster.GetProjection()
print(projRef)

what's gives me string for raster with EPSG 4326:

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"]]

and for raster with EPSG 3857:

PROJCS["WGS 84 / Pseudo-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["X",EAST],AXIS["Y",NORTH],EXTENSION["PROJ4","+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs"],AUTHORITY["EPSG","3857"]]

I guess I can do:

isInMetres = "PROJCS" in projRef

But is there any other solution? I don't consider this very readable and not sure if I can cover all corner cases this way (eg missing projRef). Dont need to be necessary with GDAL.

Answer 1

Using PyQgis API you can use the mapUnits method of QgsCoordinateReferenceSystem objects. It returns a QgsUnitTypes.DistanceUnit value, so you can use it like that for example:

# lyr is a QgsRasterLayer
crs = lyr.crs()
# crs is a QgsCoordinateReferenceSystem 
unit = crs.mapUnits()
print('Unit is {}'.format(QgsUnitTypes.toString(unit)))
# 'Unit is mètres' (i'm using french language)

Reusing your code, you can write:

isInMetres = crs.mapUnits() == 0