Hello, It is a bit of mess! As I understand it, the full rotation described is a sequence of rotations about three different axes:
Z = 90S - 90N Y' = 90W' - 90E' X" = 0E" - 180E" where it is understood that the definitions of the N-S and W-E axes change after each rotation (hence the primes and double primes). Therefore the order in which they are done matters. I suspect that the usual and assumed order is Z, Y', X"? >From the GRIB-2 stuff John posted the north_pole_grid_longitude gives the rotation about the X" axis. Something like John's "Angle of rotation" seems right to me. The apparent lack of consistency between the parameter names irks me. Perhaps one solution could be to: i) Add some text to the conventions state the order (Z, Y', X", say) and direction of rotations. ii) add three new, consistent, self-describing parameters (e.g.) angle_of_rotation_z angle_of_rotation_y angle_of_rotation_x iii) allow aliases for backwards compatibility grid_north_pole_longitude <=> angle_of_rotation_z grid_north_pole_latitude <=> angle_of_rotation_y north_pole_grid_longitude <=> angle_of_rotation_x Or would that just obfuscate things even more? All the best, David P.S. If you have a copy available, there are some nice descriptions in "Coordinate Systems and Map Projections" by D. H. Maling -- David Hassell National Centre for Atmospheric Science (NCAS) Department of Meteorology, University of Reading, Earley Gate, PO Box 243, Reading RG6 6BB, U.K. Tel : 0118 3785613 Fax : 0118 3788316 E-mail: d.c.hass...@reading.ac.uk _______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata