Lambert conformal conic projection question

To whom it may concern:

  I am curious about the contour plot for Lambert conformal conic
projection. The following is the necessary information to supply to
the ncl script. However, there is
another parameter:central latitude. As you know, when we do
projection, we need to supply:
Parallel1,
Parallel2,
central meridian,
central latitude.

I just wonder there may be some error if we don't supply centeral
latitude. I am curious how the ncl program know where is the central
latitude. I guess it might use
the average of Parallel1 and Parallel2. But this is not always true.

  res@mpProjection = "LambertConformal"
  res@mpLambertParallel1F = file1->Latin
  res@mpLambertParallel2F = file1->Latin
  res@mpLambertMeridianF = file1->Lov

Today, I am trying to use wrf_ll_to_ij to find the location of the
observational site. But it seemed there is about one grid shift compared the
way I use before. I assume the method I use before is correct. I am not sure
whether the difference may result from the central latitude issue.

 opt@MAP_PROJ = 1
   opt@TRUELAT1 = 15.0
   opt@TRUELAT2 = 40.0
   opt@STAND_LON = 114.0
   opt@REF_LAT = LAT(0,0,60,60)
   opt@REF_LON = LON(0,0,60,60)
   opt@KNOWNJ = 61
   opt@KNOWNI = 61 ; grid number, not array number, so it is 1
not 0
   opt@DX = 3000.
   opt@DY = 3000.

  opt@retrunInt = True
   loc1 = wrf_ll_to_ij( 120.978, 31.0935, opt )

Thanks

Yang

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Received on Thu Nov 19 22:39:17 2009