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20030825: where am I?

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  • Subject: 20030825: where am I?
  • Date: Mon, 25 Aug 2003 12:26:51 -0600
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
>
>
>
>