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20010411: garp and dateline

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  • Subject: 20010411: garp and dateline
  • Date: Fri, 13 Apr 2001 10:18:24 -0600

Steve,

I may be confused with what you are trying to show me.
It appears that you are trying to contour longitude. Is that correct?
The gdlist output is longitude values on a grid. If you try to contour them, you
certainly should get a bunch of contours at the dateline since you are going 
from
-179 to +179. If you are contouring values every 10, then you will get 36 
contours
jammed in at that point.

From your data you sent:
 ROW110    158.23   158.61   159.01   159.40   159.81   160.22   160.63   161.05
           161.48   161.91   162.36   162.80   163.26   163.72   164.19   164.67
           165.16   165.65   166.16   166.68   167.21   167.74   168.29   168.86
           169.44   170.03   170.63   171.25   171.89   172.55   173.22   173.92
           174.63   175.37   176.14   176.93   177.75   178.60   179.48  -179.61
          -178.65  -177.65  -176.61  -175.52  -174.38  -173.18  -171.93  -170.60
          -169.19  -167.71  -166.14  -164.47  -162.70  -160.81  -158.80  -156.65
          -154.35  -151.89  -149.25  -146.43  -143.40  -140.17  -136.73  -133.07
          -129.19  -125.12  -120.86  -116.45  -111.92  -107.32  -102.69   -98.08
           -93.55   -89.14   -84.88   -80.81   -76.93   -73.27   -69.83   -66.60
           -63.58   -60.75   -58.12   -55.65   -53.35   -51.20   -49.19   -47.30
           -45.53   -43.86   -42.29   -40.81   -39.41   -38.08   -36.82   -35.62
           -34.48   -33.39   -32.35   -31.35   -30.40   -29.48   -28.60   -27.75
           -26.93   -26.14   -25.37   -24.63   -23.92   -23.22   -22.55   -21.89
           -21.25   -20.63   -20.03   -19.44   -18.86   -18.30   -17.75   -17.21
           -16.68   -16.16   -15.66   -15.16   -14.67   -14.19   -13.72   -13.26
           -12.80   -12.36   -11.92   -11.48   -11.06   -10.63   -10.22    -9.81
            -9.41    -9.01    -8.61    -8.23

If you look at row 110, you have adjacent values of 179.48 and -179.61. I'm
assuming that is the cause of the bunch of countours you are seeing. You could
do the plotting using a discontinuous function like slt(lon,0) and sge(lon,0)
and then you wouldn't have to contour over that separation. Or you could plot
abs(lon).

Steve Chiswell
Unidata User Support






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>Keywords: 200104112005.f3BK5KL17827

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>Steve,
>  I'm not using any smoothing. I have a grid file that I created that has
>points on opposite sides of the dateline. GARP and GEMPAK will plot on
>both sides of the dateline, but it creates extra ficticious contours at
>the dateline. I've included a .gif of what's happening and I've attached
>my grid edit file. Would you mind taking a look?
>
>Thanks,
>  Steve
>
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