Hi Yang,
My understanding is that the central latitude, along with central
meridian, merely defines the origin for the rectangular projection
space, but otherwise does not materially affect the shape of
projection. Thus I can see it would make a big difference in what gets
returned from a calculation like wrf_ll_to_ij(), but I wouldn't expect
it to affect the shape and positioning of a contour plot (?)
Is that what you are seeing -- some differences in the alignment or
shape of the contour plot?
Rick
On Nov 19, 2009, at 10:39 PM, Yang Gao wrote:
> 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
>
>
> _______________________________________________
> ncl-talk mailing list
> List instructions, subscriber options, unsubscribe:
> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
_______________________________________________
ncl-talk mailing list
List instructions, subscriber options, unsubscribe:
http://mailman.ucar.edu/mailman/listinfo/ncl-talk
Received on Fri Nov 20 09:28:09 2009
This archive was generated by hypermail 2.1.8 : Mon Nov 23 2009 - 12:24:02 MST