| Cylindrical Equal Area projection [message #80157] |
Tue, 15 May 2012 20:41 |
envi35@yahoo.ca
Messages: 48
Registered: March 2005
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Hi, I'm trying to draw grids on some maps I downloaded from NSIDC in
EASE-grid (northern hemisphere 25km). I set up the EASE-grid map
projection in IDL8.0 as:
; Set up the EASE-grid map projection.
mapStruct = Map_Proj_Init("Cylindrical Equal
Area",semimajor_axis=6371228,$
semiminor_axis=6371228,CENTER_LONGITUDE=0.0,
standard_parallel=60.0,$
false_easting=0.0,false_northing=0.0)
; Convert the corner lat/lon points to XY coordinates.
lonCorners = [lons[0,0], lons[459,0], lons[459,534], lons[0,534]]
latCorners = [lats[0,0], lats[459,0], lats[459,534], lats[0,534]]
xy = Map_Proj_Forward(lonCorners, latCorners,
MAP_STRUCTURE=mapStruct)
; Find the x and y scale from one pixel to the next.
xscale = Abs((xy[0,1] - xy[0,0]) / (s[0]-1))
yscale = Abs((xy[1,3] - xy[1,0]) / (s[1]-1))
print,xscale,yscale
The xscale and yscale should both be 25000m, but I got
12.413577 172.70326. I tried to change the standard_parallel,
such as 90.0, 70.0, 45.0... but none seems to give the correct xscale/
yscale. What is problem? Anybody have success with this newly added
projection?
Thanks in advance!
Jenny
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