20001205: McIDAS-X GRDCOPY with MATH questions (cont.)

>From: Mark Lilly <address@hidden>
>Organization: UVa
>Keywords: 200012042120.eB4LKHo05867 McIDAS-X 7.6 GRDCOPY MATH=

Mark,

>I would like to thank you for helping us out with our problem.
>I really appreciate it.

No problem.

>I now know about the difference between the two grid
>types.

I have already talked to SSEC about the inability to select the correct
grid projection (e.g., 211 vs 212, etc.) through a McIDAS SELect key.

>There still is one question and that is that on the grids that are
>spaced 25 mb apart, I cannot do any Math between them.  I am currently
>using the grids that are spaced 50 mb apart and they work fine but the 25
>mb ones are still causing problems.  Anyway this might be something for a
>later time.

I just did the following simple test of your assertion:

GRDLIST PEL/ETA.1 FORM=ALL GRID=317 318
Dataset position 1      Directory Title= Eta archive
PAR    LEVEL       DAY        TIME    SRC FHOUR     FDAY       FTIME  GRID  PRO
---- --------- ------------ -------- ---- ----- ------------ -------- ----- ----
T     775 MB   29 JUN 00181 00:00:00  ETA     0 29 JUN 00181 00:00:00   317 LAMB
Total pts= 23865 Num rows= 129  Num columns= 185    received:  2000181 021616Z
Temperature
GRIB ID numbers: Geographic =212; PAR = 11; Model ID = 84; Level type =100
Units of gridded variable are K    Scale of variable is:   2
Lambert Conformal Tangent Cone Projection
Row num of pole= -226.67  Col num of pole=  105.00  Col spacing (m)= 40635.0
Standard Latitudes=   25.00     25.00   Standard Longitude=   95.00
PAR    LEVEL       DAY        TIME    SRC FHOUR     FDAY       FTIME  GRID  PRO
---- --------- ------------ -------- ---- ----- ------------ -------- ----- ----
T     750 MB   29 JUN 00181 00:00:00  ETA     0 29 JUN 00181 00:00:00   318 LAMB
Total pts= 23865 Num rows= 129  Num columns= 185    received:  2000181 021616Z
Temperature
GRIB ID numbers: Geographic =212; PAR = 11; Model ID = 84; Level type =100
Units of gridded variable are K    Scale of variable is:   2
Lambert Conformal Tangent Cone Projection
Row num of pole= -226.67  Col num of pole=  105.00  Col spacing (m)= 40635.0
Standard Latitudes=   25.00     25.00   Standard Longitude=   95.00
Number of grids listed = 2
GRDLIST - done

So, these two T grids are 25 mb apart (775 mb and 750 mb) and are on
the same projection (212 grid).  I then did a simple differencing
between these:

GRDCOPY PEL/ETA.1 MYDATA/GRIDS.9001 G1='GRID 317' G2='GRID 318' MATH='(G1-G2)' 
NEWPAR=DIFF K 925 MB

GRDLIST MYDATA/GRIDS.9001 NUM=ALL
Dataset position 9001   Directory Title=
PAR    LEVEL       DAY        TIME    SRC FHOUR     FDAY       FTIME  GRID  PRO
---- --------- ------------ -------- ---- ----- ------------ -------- ----- ----
FP    925 MB   29 JUN 00181 00:00:00  ETA     0 29 JUN 00181 00:00:00     1 LAMB
SP    925 MB   29 JUN 00181 00:00:00  ETA     0 29 JUN 00181 00:00:00     2 LAMB
ONE   925 MB   29 JUN 00181 00:00:00  ETA     0 29 JUN 00181 00:00:00     3 LAMB
DIFF  925 MB   29 JUN 00181 00:00:00  ETA     0 29 JUN 00181 00:00:00     4 LAMB
Number of grids listed = 4
GRDLIST - done

GRDLIST MYDATA/GRIDS.9001 PARAM=DIFF FORM=ALL
Dataset position 9001   Directory Title=
PAR    LEVEL       DAY        TIME    SRC FHOUR     FDAY       FTIME  GRID  PRO
---- --------- ------------ -------- ---- ----- ------------ -------- ----- ----
DIFF  925 MB   29 JUN 00181 00:00:00  ETA     0 29 JUN 00181 00:00:00     4 LAMB
Total pts= 23865 Num rows= 129  Num columns= 185    received:  2000181 021616Z
GRIB ID numbers: Geographic =212; PAR = 11; Model ID = 84; Level type =100
Units of gridded variable are K    Scale of variable is:   5
Lambert Conformal Tangent Cone Projection
Row num of pole= -226.67  Col num of pole=  105.00  Col spacing (m)= 40635.0
Standard Latitudes=   25.00     25.00   Standard Longitude=   95.00
Number of grids listed = 1
GRDLIST - done

GRDDISP MYDATA/GRIDS.9001 PARAM=DIFF MAP=NACONF CINT=1
GRDDISP: Done with graphic frame 1
GRDDISP - done

The simple differencing appears to work fine.  Can you provide me with
an example of what is not working for you?  Did you check to make sure
that the two grids that you are trying to difference are on the same
projection.

>Thanks for clearing up the problem.

You are welcome.

Tom