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>From: address@hidden (Chris Hennon) >Organization: UCAR/Unidata >Keywords: 200102161840.f1GIeUL27371 >Steve - > >Perhaps you can clear up a bit of confusion I'm having with gdlist. I >have a NCEP Reanalysis gempak formatted file (global domain), and I'm >trying to list out the data for the domain 0;-100;50;-1.5 : > >Creating process: gplt for queue 2226552 > GDATTIM Grid date/time 980601/0000 > GLEVEL Grid level 500 > GVCORD Grid vertical coordinate pres > GFUNC Scalar grid tmpk > GDFILE Grid file tempk_199806.gem > GAREA Graphics area 0;-100;50;-2.5 > PROJ Map projection/angles/margins|dr CED > SCALE Scalar scale / vector scale 0 > OUTPUT Output device/filename t > >According to my hand calculations, it should give me back rows 57 thru 37 >(21 rows), since the dataset has 2.5 degree resolution. Instead it >returns rows 58 thru 36 (23 rows). If you use GFUNC=mul(latr,rtd) it shows that it is giving you rows for 52.5 to -2.5 degrees latitude. The $GEMPAK/source/gemlib/dg/dgarea.f subroutine is adding 1 "EXTEND" distance to all sides for the subset area. Without doing this, you would not be able to compute values if you gfunc() involved a dirivative adjacent to a subset boundary (that is, when the GAREA is set, the computations only occur on the subset grid, so the subset grid must include the adjacent rows in order to compute dirivaties in functions). In this case, you are using GFUNC=tmpk which doesn't involve a gradient, but if you used gfunc = avor(wnd) or grad(tmpk), etc you would need the extra row in order to use a centered finite difference formula instead of a left or right finite difference. This is more important in gdcntr etc where your contours go up to the boundary. >Furthermore, the data values in row 58 >do not match the data values in row 58 when I use GAREA = dset. What >exactly is gdlist doing here? Thanks. They appear the same too me.... however, you may be looking in the wrong location. When you use your garea, you are gettings COLUMNS 104 to 144. When you use GAREA=dset, you are getting COLUMNS 1 to 144. So the value that is at ROW 58 column 104 in the output with your subset garea is the first value listed. But, when garea=dset, it is at the end of the 13th line of output for ROW 58. Let me know if your output does not match this! > >Chris > >================================================ >| Chris Hennon Ohio State University | >| Tropical Meteorology address@hidden | >| | >| Dept of Geography Office: 1155 Derby Hall | >| 1036 Derby Hall Phone : (614) 292-2704 | >| Columbus, OH 43210 Fax : (614) 292-6213 | >================================================ > Steve Chiswell