Rotated grid transform

Transforms coordinates from regular to rotated grid and vice versa.

This functions transforms a set of coordinates in regular lon/lat degrees, grid_in = [lon, lat], to a set of coordinates in rotated lon/lat degrees, grid_out = [lon', lat'], and vice versa:

[grid_out] = rotated_grid_transform(grid_in, option, SP_coor)

where option is the 'direction' of the transform (1: regular -> rotated and 2: rotated -> regular) and SP_coor are the coordinates of the South Pole in the rotated grid [SP_lon, SP_lat]

Example:
SP_coor = [18 -39.3];
grid_in = [[12; 12; 12],[55; 54; 53]];
[grid_out] = rotated_grid_transform(grid_in, 1, SP_coor)

grid_out =

-3.4476 4.4397
-3.5289 3.4430
-3.6100 2.4463

grid_in = grid_out;
[grid_out] = rotated_grid_transform(grid_in, 2, SP_coor)

grid_out =

12.0000 55.0000
12.0000 54.0000
12.0000 53.0000

Reference:
http://gis.stackexchange.com/questions/10808/lon-lat-transformation/14445