Update reader for MODIS Level 3 files in CMG format.

satpy/etc/readers/modis_l3.yaml

@@ -0,0 +1,16 @@
+reader:
+  name: modis_l3
+  short_name: MODIS l3
+  long_name: MODIS Level 3 (mcd43) data in HDF-EOS format
+  description: MODIS HDF-EOS L3 Reader
+  status: Beta
+  supports_fsspec: false
+  reader: !!python/name:satpy.readers.yaml_reader.FileYAMLReader
+  sensors: [modis]
+
+file_types:
+  mcd43_cmg_hdf:
+    file_patterns:
+    - 'MCD43C{prod_type}.A{start_time:%Y%j}.{collection:03d}.{production_time:%Y%j%H%M%S}.hdf'
+    - 'M{platform_indicator:1s}D09CMG.A{start_time:%Y%j}.{collection:03d}.{production_time:%Y%j%H%M%S}.hdf'
+    file_reader: !!python/name:satpy.readers.modis_l3.ModisL3GriddedHDFFileHandler

satpy/readers/modis_l3.py

@@ -61,11 +61,22 @@ def __init__(self, filename, filename_info, filetype_info, **kwargs):
         # Get the grid resolution
         pos = gridname.rfind("_") + 1
         pos2 = gridname.rfind("Deg")
-        self.resolution = float(gridname[pos:pos2])
+
+        # Some products don't have resolution listed.
+        if pos < 0 or pos2 < 0:
+            self.resolution = 360. / self.ncols
+        else:
+            self.resolution = float(gridname[pos:pos2])
 
         upperleft = self.metadata["GridStructure"]["GRID_1"]["UpperLeftPointMtrs"]
         lowerright = self.metadata["GridStructure"]["GRID_1"]["LowerRightMtrs"]
 
+        # For some reason, a few of the CMG products multiply their
+        # decimal degree extents by one million. This fixes it.
+        if lowerright[0] > 1e6:
+            upperleft = tuple(val / 1e6 for val in upperleft)
+            lowerright = tuple(val / 1e6 for val in lowerright)
+
         self.area_extent = (upperleft[0], lowerright[1], lowerright[0], upperleft[1])