[ferret_users] restrict polymark to transect

[Marco van Hulten <marco.van-hulten@xxxxxxxxxxxx>]

Hello,

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?

Or should I remove these data in an earliers stage of my script?
In other words, I have the coordinates of the transect stations, say
(lon_stat, lat_stat), and many more of the larger observational
dataset, say (lon_data, lat_data).  How to restrict (lon_data,
lat_data) to be near (lon_stat, lat_stat)?

Any ideas to go about doing this are welcome.

Marco

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