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20000920: selective filtering for sfmap

>From: address@hidden (William Gallus)
>Organization: UCAR/Unidata
>Keywords: 200009201358.e8KDwHb22600

>Hello,
>
>Is there a way to have gempak "selectively" filter entire obs when
>doing a map within SFMAP?   I am trying to create easy to read maps
>like WXP used to produce, for use in a junior-level meteo class where 
>students will have to contour pressure and temperature and then analyze
>fronts on the maps.   I have not been able to create useable maps
>with gempak this way......because the FILTER function randomly deletes
>info.   This means that it might not show the pressure at many points,
>and this is vital info for the lab exercise.   I'd rather have it either
>show the entire station plot, or skip it entirely.  
>
>Bill
>**********************************************
>*  Bill Gallus                               *
>*  Asst. Prof. of Meteorology                *
>*  Dept. of Geological and Atmospheric Sci.  *
>*  3025 Agronomy Hall                        *
>*  Iowa State University                     *
>*  Ames, IA 50011                            *
>*  (phone) 515-294-2270                      *
>*  (fax)   515-294-2619                      *
>**********************************************
>


Bill,

If you want to plot a map of PMSL, and filter stations- while only
displaying those stations that actually report PMSL, you can use:

sfparm=pmsl>0

or for tmpc:
sfparm = tmpc>-200

or for both pmsl and tmpc:
sfparm = ;pmsl>0;;tmpc>-200


Filter does not radndomly delete data. However, it does interpret
"BLNK" differently that "SPAC" or a missing PMSL when checking for overlapping.
Stations are plotted in the order they are found in the surface file (which is 
the 
order they are in the station table....generally alphabetical). If you wanted
first order stations to always be found before secondary stations, you could 
order
the table that way. That would ensure that a station such as DEN for example
would get plotted before a little airport like APA- and therefore the filter
would be less likely to have overlap with the the first order stations.

Steve Chiswell
Unidata User Support