From Marina Levy's programs
Sebastien Masson (smasson@lodyc.jussieu.fr):
Validation. 5/6/2000
Known issues
Todo items
seb: nom du input?
Restrictions
Force parameters of the zoom on the grid V to be the same as
those on the grid T.
Points which can not be calculated are put at the value NaN
consecrated by IDL: !values.f_nan