* Using OpenGrADS [#fdf9f2c5]

- For me, only for calculation of stream function and velocity potential...
- Official site: http://opengrads.org

** Installation [#u9907509]
All examples are for grads-1.9 on Linux-PC, located at ~/GrADS.
+ Save the original grads directory at somewhere else (just in case).
+ Get appropriate executables from [[here:http://sourceforge.net/projects/opengrads/files/grads1/grads-1.9.0-rc1-bin-i686-pc-linux-gnu.tar.gz/download]], and copy the contents in bin directory to ~/GrADS/bin (overwrite them).
+ Get appropriate extensions from [[here:http://sourceforge.net/projects/opengrads/files/extensions/grads-1.9.0-rc1-gex-r2-i686-pc-linux-gnu.tar.gz/download]], and copy the contents in bin directory to ~/GrADS/bin (there should be no file with same name).
+ Set environmental variables as follows:~
** Drawing stream function [#ba64e112]
 $ gradsnc 
    # be sure the opengrads command is executed
 > open pgb.ctl 
    # example
 > d fish_psi(ugrdprs,vgrdprs)
 It's usual to shift the field to its global average being a zero.
 > a=fish_psi(ugrdprs,vgrdprs)
 > d a-aave(a,global)