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Hi Mark- I'm sorry for the delay in responding to this. I've been trying to get my head around the projection information and how we could support these sigma levels in a non-regular grid. > > The projection defines the region of coverage. The number of gridpoints > > will determine the resolution. So presumably when they went from 30km > > to 20km, there were more grid points in the x and y direction. > > > > The projection should define the region of coverage. > > > > I must be missing something then. The projection attributes which I am > using do not define the region of coverage, but instead cover the > characteristics of the projection. > > My projection attributes: > char polar_stereographic ; > polar_stereographic:grid_mapping_name = "polar_sterographic" ; > polar_stereographic:straight_vertical_longitude_from_pole = 180.f ; > polar_stereographic:latitude_of_projection_origin = -90.f ; > polar_stereographic:scale_factor_at_projection_origin = 1.f ; > polar_stereographic:false_easting = 0.f ; > polar_stereographic:false_northing = 0.f ; the x and y coordinates need to be in kilometers on the projection plane for this to work. Sorry for the confusion. > I selected these attributes from the CF 1.0 instructions: > http://www.cgd.ucar.edu/cms/eaton/cf-metadata/CF-1.0.html > Polar stereographic > grid_mapping_name = polar_stereographic > Map parameters: > * straight_vertical_longitude_from_pole > * latitude_of_projection_origin - Either +90. or -90. > * Either standard_parallel or scale_factor_at_projection_origin > * false_easting > * false_northing > Map coordinates: The x (abscissa) and y (ordinate) rectangular > coordinates are identified by the standard_name attribute values > projection_x_coordinate and projection_y_coordinate respectively. > > I went ahead and removed all lat lon references. This included the lat > lon variables and associated attributes, as well as the coordinates > attribute (lat lon) for each variable. These changes are included in > the file: 20050601.nc > The result was a step backwards as when attempting to open in the Data > Chooser, I get the error: > No gridded data found for: > /vardar/data4/seefeldm/amps/20050601.nc > Are you sure this is a gridded file? Okay, my bad. > I tried one more time time with the coordinates attribute specifying xc > and yc for each variable, the rectangular coordinates. These changes > are included in the file: 20050801.nc > I receive the same error as without the coordinate attributes set: > No gridded data found for: > /vardar/data4/seefeldm/amps/20050801.nc > Are you sure this is a gridded file? > > These nc files can be retrieve from: > http://foehn.colorado.edu/antarctica/amps/nc/ > -The file 20050701.nc is the original file I created to work on this > problem. There's a typo in this file that keeps the IDV from picking up the projection corretly. In your projection variable: grid_mapping_name should be :stereo" not "stero", so projection not found char polar_stereographic; :grid_mapping_name = "polar_sterographic"; Then, if you can get the xc and yc to be the values of the grid in kilometers on the projection instead of grid row/column, you should be in better shape. If i just change the unit of these to km, I was able to get something to plot on sigma coords (although not in the right place). You might be able to just add scale_factor and add_offset attributes to the xc/yc variables. If you need more help with that, let me know. Don > -I have no idea as to why the file sizes are so drastically different. > Other than than the defining of the attributes, and the removal of the > lat lon fields, all other code used in creating the netcdf file is the same. > > Mark > > Ticket Details =================== Ticket ID: FGA-644757 Department: Support IDV Priority: Critical Status: Open