nelliott13

Projecting "rotated pole" coordinate system (from netCDF)

Discussion created by nelliott13 on Nov 21, 2011
Latest reply on Oct 25, 2019 by KatyAppletonUEA
Hello-

Neither ArcGIS 9.3x or 10 seem to handle the importation of a netCDF file with a "rotated pole" coordinate system, listing the coordinate system as "unknown" in the data source tab.  Barring an automatic fix allowing the program to correctly read these data, how would I go about manually defining a projection so that they display properly?

The projection metadata provided in the netCDF file are as follows:
   char rotated_pole;
     :grid_mapping_name = "rotated_latitude_longitude";
     :grid_north_pole_latitude = 42.5; // double
     :grid_north_pole_longitude = 83.0; // double
     :_CoordinateTransformType = "Projection";
     :_CoordinateAxisTypes = "GeoX GeoY";

This is not enough information, in and of itself, to define a specific projection, which is probably why ArcGIS is having the problem.  Looking at the CF Metadata convention (specifically Appendix F), it appears that a third parameter of north_pole_grid_longitude defaults to 0 if not specified. 

I think these three parameters should be enough to manually define the projection, but I'm unsure of how to do so.  In the 'Define Projection' tool, what projected coordinate system should I select as a base?  There are no "rotated_pole" or "rotated_latitude_longitude" or "arctic somethingorother"...

Oh, and the purpose of defining the coordinate system is more so that I can project other things into the same coordinate system (for example a polygon representing the extent of the studyarea so that I can clip the netCDF data).

I apologize if this question has been asked/answered elsewhere, and thanks for your time!

Sincerely,
Nathan Elliott

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