Hi. Is it possible that we just need to loosen the definition of projection_x_coordinate and projection_y_coordinate?
Jim [image: CICS-NC] <http://www.cicsnc.org/>Visit us on Facebook <http://www.facebook.com/cicsnc> *Jim Biard* *Research Scholar* Cooperative Institute for Climate and Satellites NC <http://cicsnc.org/> North Carolina State University <http://ncsu.edu/> NOAA National Centers for Environmental Information <http://ncdc.noaa.gov/> *formerly NOAA’s National Climatic Data Center* 151 Patton Ave, Asheville, NC 28801 e: [email protected] o: +1 828 271 4900 *Connect with us on Facebook for climate <http://www.facebook.com/NOAANCEIclimate> and ocean and geophysics <http://www.facebook.com/NOAANCEIoceangeo> information, and follow us on Twitter at @NOAANCEIclimate <http://www.twitter.com/NOAANCEIclimate>and @NOAANCEIocngeo <http://www.twitter.com/NOAANCEIocngeo>.* On Tue, Apr 10, 2018 at 1:33 PM, Ethan Davis <[email protected]> wrote: > Hi Randy, > > This projection was added to CF with Trac #72 > <https://cf-pcmdi.llnl.gov/trac/ticket/72>. There's some discussion > around the x,y coordinates. I think comment 12 > <https://cf-pcmdi.llnl.gov/trac/ticket/72#comment:12> from John Caron > addresses the issue of using radians instead of meters: > > "Ideally they would be something like "km on the projection plane", but > then (I think) you need scaling factors that depend on the instrument. If > you include the scaling factors into the coordinates, then you have (I > guess) radians." > > > Cheers, > > Ethan > > On Tue, Apr 10, 2018 at 8:09 AM, Randy Horne <[email protected]> > wrote: > >> Ethan: >> >> What you suggest is fine. >> >> As an aside …. >> If you look at the CF standard name table, the canonical units for >> standard name “ projection_x_coordinate” and “projection_y_coordinate” are >> meters (not radians). >> >> The GOES-R designers (specifically me) inadvertently used these two >> standard names, not realizing they should NOT have used them because a >> standard name can not have two different canonical units. >> >> Now, because the GOES-R system is already operational and in use, it >> would be major rework for GOES-R to use a yet to be defined standard name >> (such as projection_x_angilar_coordinate and >> projection_y_angular_coordinate). >> >> >> Not sure what to d about this …. >> >> >> >> v/r >> >> randy >> >> >> >> On Apr 9, 2018, at 3:54 PM, Ethan Davis <[email protected]> wrote: >> >> Hi all, >> >> The "Geostationary projection" section of Appendix F "Grid Mappings" says >> >> The x (abscissa) and y (ordinate) rectangular coordinates are identified >> by the standard_name attribute values projection_x_coordinate and >> projection_y_coordinate respectively. In the case of this projection, the >> projection coordinates in this projection are directly related to the >> scanning angle of the satellite instrument, and their units are radians. >> >> >> To more explicitly fit CF expectations for units of variables with a >> standard_name attribute, I believe the last bit should read: >> >> ... and their *canonical* units are radians. >> >> >> This came up because the GOES-16 Full Disk data (example below [1]) is >> stored with the projection_{x|y}_coordinate values in microradians and, it >> turns out, the netCDF-Java code didn't like that as it expected radians. >> (Oops!) >> >> Unless anyone disagrees, I will open a CF Trac ticket for this change >> later this week. >> >> Thanks, >> >> Ethan >> >> [1] >> http://thredds-test.unidata.ucar.edu/thredds/dodsC/satellite >> /goes16/GOES16/FullDisk/Channel08/20180406/GOES16_ >> FullDisk_20180406_201540_6.19_6km_0.0S_75.0W.nc4.html >> >> netcdf GOES16_FullDisk_20180406_201540_6.19_6km_0.0S_75.0W { >> dimensions: >> x = 1808 ; >> y = 1808 ; >> variables: >> int time ; >> time:units = "seconds since 2017-01-01" ; >> time:standard_name = "time" ; >> time:long_name = "The start date / time that the satellite began >> capturing the scene" ; >> time:axis = "T" ; >> time:calendar = "standard" ; >> short y(y) ; >> y:standard_name = "projection_y_coordinate" ; >> y:units = "microradian" ; >> y:scale_factor = -167.999999999971 ; >> y:add_offset = 151788. ; >> short x(x) ; >> x:standard_name = "projection_x_coordinate" ; >> x:units = "microradian" ; >> x:scale_factor = 167.999999999971 ; >> x:add_offset = -151788. ; >> int fixedgrid_projection ; >> fixedgrid_projection:grid_mapping_name = "geostationary" ; >> fixedgrid_projection:latitude_of_projection_origin = 0. ; >> fixedgrid_projection:longitude_of_projection_origin = -75. ; >> fixedgrid_projection:semi_major = 6378137. ; >> fixedgrid_projection:semi_major_axis = 6378137. ; >> fixedgrid_projection:semi_minor = 6356752.31414 ; >> fixedgrid_projection:semi_minor_axis = 6356752.31414 ; >> fixedgrid_projection:perspective_point_height = 35785831. ; >> fixedgrid_projection:sweep_angle_axis = "x" ; >> short Sectorized_CMI(y, x) ; >> Sectorized_CMI:_FillValue = 0s ; >> Sectorized_CMI:standard_name = "brightness_temperature" ; >> Sectorized_CMI:units = "kelvin" ; >> Sectorized_CMI:grid_mapping = "fixedgrid_projection" ; >> Sectorized_CMI:add_offset = 138.05f ; >> Sectorized_CMI:scale_factor = 0.04224986f ; >> Sectorized_CMI:valid_min = 0s ; >> Sectorized_CMI:valid_max = 4095s ; >> Sectorized_CMI:coordinates = "time y x" ; >> >> // global attributes: >> :title = "Sectorized Cloud and Moisture Imagery for the EFD region." ; >> :ICD_version = "GROUND SEGMENT (GS) TO ADVANCED WEATHER INTERACTIVE >> PROCESSING SYSTEM (AWIPS) INTERFACE CONTROL DOCUMENT (ICD) Revision B" ; >> :Conventions = "CF-1.6" ; >> :channel_id = 8 ; >> :central_wavelength = 6.19f ; >> :abi_mode = 3 ; >> :source_scene = "FullDisk" ; >> :periodicity = 15.f ; >> :production_location = "RBU" ; >> :product_name = "EFD-060-B12-M3C08" ; >> :satellite_id = "GOES-16" ; >> :product_center_latitude = 0. ; >> :product_center_longitude = -75. ; >> :projection = "Fixed Grid" ; >> :bit_depth = 12 ; >> :source_spatial_resolution = 2.f ; >> :request_spatial_resolution = 6.f ; >> :start_date_time = "2018096201540" ; >> :number_product_tiles = 4 ; >> :product_tile_width = 1024 ; >> :product_tile_height = 1024 ; >> :product_rows = 1808 ; >> :product_columns = 1808 ; >> :pixel_x_size = 6. ; >> :pixel_y_size = 6. ; >> :satellite_latitude = 0. ; >> :satellite_longitude = -75. ; >> :satellite_altitude = 35785831. ; >> :created_by = "ldm-alchemy" ; >> :product_tiles_received = 4 ; >> } >> >> _______________________________________________ >> CF-metadata mailing list >> [email protected] >> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata >> >> >> _____________________________________ >> >> Randy C Horne ([email protected]) >> Principal Engineer, Excalibur Laboratories Inc. >> voice & fax: (321) 952.5100 >> cell: (321) 693.1074 >> url: http://www.excaliburlabs.com >> >> >> >> > > _______________________________________________ > CF-metadata mailing list > [email protected] > http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > >
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