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.hassell at reading.ac.uk
Received on Wed Mar 06 2013 - 11:29:47 GMT
