Use full projection string for gdalbuildvrt.

Sometimes two projections have the same name, but different internal
parameters, which would cause gdalbuiltvrt to fail because it can handle
only one projection in a VRT file.  So now we use the full WKT string
to describe the projection.

scripts/run_prominence.py

@@ -44,9 +44,6 @@ def round_up(coord, interval):
     """Return coord rounded up to the nearest interval"""
     return math.ceil(coord / interval) * interval
 
-def sign(a):
-    return bool(a > 0) - bool(a < 0)
-
 def filename_for_coordinates(x, y, degrees_per_tile):
     """Return output filename for the given coordinates"""
     y += degrees_per_tile  # Name uses upper left corner
@@ -122,7 +119,11 @@ def create_vrts(tile_dir, input_files, skip_boundary):
         ds = gdal.Open(input_file)
         prj = ds.GetProjection()
         srs = osr.SpatialReference(wkt=prj)
-        projection_name = srs.GetAttrValue('projcs')
+        # gdalbuildvrt needs the projections to match pretty much exactly within a VRT file.
+        # It's not enough to use the projection name; sometimes two projections have the
+        # same name but slightly different datums, and gdalbuildvrt will fail.
+        # So instead we use the whole WKT string.
+        projection_name = srs.ExportToWkt()
         projection_map.setdefault(projection_name, []).append(input_file)
 
     # For each projection, build raw and warped VRTs