;+ ;PROCEDURE: add_bdir,dat,source ;PURPOSE: ; Adds magnetic field direction [theta,phi] to a 3d structure ; The new structure element will be a two element vector [theta,phi] ; with the tag name 'bdir'. ;INPUT: ; dat: 3D data structure (i.e. from 'GET_EL') ; [source] : String index that points to magnetic field data. ;Notes: ; Magnetic field data must be loaded first. ; See 'GET_MFI' ;- pro add_bdir,dat,source if not keyword_set(source) then source = 'Bexp' t = (dat.time+dat.end_time)/2 b = data_cut(source,t) cart_to_sphere,b(0),b(1),b(2),r,th,ph bdir = [th,ph] str_element,/add,dat,'bdir',bdir end