Re: [ferret_users] restrict polymark to transect

[Ryo Furue <furue@xxxxxxxxxx>]

Hi Marco,

> I regularly plot transects of model output with observations plotted on
> top of these as dots.  So the last command is
>
>   go polymark polygon/over Latitude, Depth, myvar circle 1.0
>
> for a transect that is monotonic in latitude.  Observational data from
> all longitudes are plotted.  This works fine when using only the
> transect observational data.  If I use a dataset that includes
> observations at longitudes far away from the transect (but within the
> latitude range of the transect), these are also included on the plot.
>
> While this is expected behaviour, I would like to limit the longitudes
> to close to the transect.  So I am thinking of including a criterium
> that limits plotting of points near the transect.  How would such a
> criterium look like?

I guess you want something like this:

yes? let a = {1, 2, 3, 4, 5}
yes? let b = {1, -2, 2, 3, -1}
yes? let a_with_positive_b = if b gt 0 then a  ! if b > 0
yes? list a_with_positive_b
             VARIABLE : IF B GT 0 THEN A
             SUBSET   : 5 points (X)
 1   / 1:  1.000
 2   / 2:   ....
 3   / 3:  3.000
 4   / 4:  4.000
 5   / 5:   ....
yes?

Basically you want only that part of a variable for which another
variable takes certain values.  The above strategy works when the two
variables share a common shape.

Ryo
-------
By the way, I'm interested in your "criterium", which looks as if it
is a Latin version of the Greek word "criterion" (the Latin "-um" is
the same thing as the Greek "-on").