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Ruth, You can look at the latitude and longitudes of the grid points displayed using the GFUNC(s): mul(latr,RTD) mul(lonr,RTD). In GDLIST, since the program can calculate quantities (in addition to showing you data values in your grid), EXTEND is provided for the extra padded row/columns so that you can calculate quantities with differentials and second order functions on the subsetted grid. Steve Chiswell >From: Ruth Platner <address@hidden> >Organization: UCAR/Unidata >Keywords: 200308251459.h7PExhLd023830 >Hi, > >I'm using gdlist to retrieve data from a gempak file. Here's the header >of the output from gdlist: > >--------------- > > Grid file: /afer/rlp/monthlyrean/2001.gpcprain.sfc.gem > GRID IDENTIFIER: > TIME1 TIME2 LEVL1 LEVL2 VCORD PARM >950401/0000 950401/0000 0 NONE AVE_PR-- > AREA: 20;85;60;150 GRID SIZE: >144 73 > COLUMNS: 34 62 ROWS: 44 62 > > Scale factor: 10** 5 > >--------------------------- > >Notice I've requested data from 20 to 60 in latitude and from 85 to 150 >in longitude. If gdlist only returned data for the area requested, then >I should have received 27 columns instead of 29 and 17 rows instead of >19. I am assuming that the extra points surround the requested data >symmetrically. So I'm assuming that gdlist has returned data from 82.5 >to 152.5 in longitude and from 17.5 to 62.5 in latitude. Is this >correct? I did notice that when I request data at the edge of the grid, >at 0 longitude, that the extra points seem to not be symmetrical, I >assume that this is because I've reached the edge of the grid. Maybe I'm >confused about that. But my real question here is when I request an area >from gdlist and then receive a set of data that is larger than the >requested area, how can I know for sure where my requested data lie >within the slightly larger returned area. > >I thought I had this all figured out, but when I plotted data from >gdlist and compared that plot to a figure made from the same data, but >without the involvement of gempak and gdlist, the two plots seem to be >slightly offset. > >Thanks for your help, > >Ruth > > > >