force numpy array to be float to use nans

stable_night_lights/nightlights_file_extraction.py

@@ -36,7 +36,7 @@ def read_proxydata(filename, dummy=DEBUG and USE_DUMMY_STABLE_NIGHT_LIGHTS_DATA)
     dlon, dlat = rst.scale  # xscale=dlon, yscale=dlat
 
     # construct data array and lonvec, latvec
-    data = rst.bands[0].data()
+    data = rst.bands[0].data().astype(np.float)
     nodata_value = rst.bands[0].nodata_value
     data[data == nodata_value] = np.nan
     lonvec = np.linspace(xmin, xmax, cols)