This is an obscure question that I am sure will be of interest only to the
weather weenies out there.
I am trying to plot some gridded data from the NCEP Eta/NAM high-resolution
model. This model uses WMO grid 218, which is defined on a Lambert conformal
map projection by the following:
---------------------------------------------------------
VALUE - 218 (B)[B]
GRID DESCRIPTIONS - Grid over the Contiguous United States (used by the 12-km
Eta Model) (Lambert Conformal)
Nx 614
Ny 428
La1 12.190N
Lo1 226.514E = 133.459W
Res. & Comp. Flag 0 0 0 0 1 0 0 0
Lov 265.000E = 95.000W
Dx 12.19058 km
Dy 12.19058 km
Projection Flag (bit 1) 0 (not bipolar)
Scanning Mode (bits 1 2 3) 0 1 0
Lat/lon values of the corners of the grid
(1,1) 12.190N, 133.459W
(1,428) 54.564N, 152.878W
(614,428) 57.328N, 49.420W
(614,1) 14.342N, 65.127W
Pole point
(I,J) (347.668, 1190.097)
The Dx, Dy grid increment (at 25 deg north) was selected so that the grid
spacing would be exactly 12.000 km at 35 deg north; the intersection of 35N &
95W falls on point (347.668, 160.999)
---------------------------------------------------------
If the map projection is set correctly, the four corners in the table above
should define a rectangle on the map. Using my best guess, I get something that
is close, but not quite right.
PRO NAM_CONIC
MAP_SET, /CONIC, 35.0, -95.0, STANDARD = [35.0], /GRID, /USA, /CONT, SCALE =
5.0E7
x = [-133.459, -152.878, -49.420, -65.127]
y = [ 12.190, 54.464, 57.328, 14.342]
PLOTS, [x, x[0]], [y, y[0]]
FOR i = 0, 3 DO BEGIN
uv = CONVERT_COORD(x[i], y[i], /DATA, /TO_NORMAL)
PRINT, x[i], y[i], uv[0], uv[1]
ENDFOR
END
Does anyone know how to use MAP_SET or MAP_PROJ_INIT to define the correct map
projection for this grid?
I guess what I am asking is how to get p0_lat, p0_lon, rot, and the standard
parallel(s) from the information in the table.
Ken Bowman
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