Re: lambert conformal coordinates

Micah,

Indeed it is inefficient to search through coordinate arrays.
However, NCL provides the function getind_latlon2d to do this with
some efficiency. For small numbers of points to locate, the run
time should be insignificant. Also look at the functions
wrf_ll_to_ij and
wrf_user_ll_to_ij if you are working with WRF data.

If you have to search for huge numbers of points, only then might it
be worth the time to figure out the transformation equations.

--Dave

On 10/19/2011 1:48 PM, Micah Sklut wrote:
> Hi Dave,
>
> Thanks for your reply. The data set does lnclude lat/lon arrays
> containing all the grid point coordinates.
> So your suggestion is to loop through these arrays, until finding
> the proper x/y coordinate?
>
> It certainly would not be as efficient to loop through the arrays as
> compared to an equation, but should work just fine.
>
> Micah
>
>
> On Wed, Oct 19, 2011 at 3:32 PM, Dave Allured <dave.allured@noaa.gov
> <mailto:dave.allured@noaa.gov>> wrote:
>
> Micah,
>
> Does the data set come with coordinate variables containing the
> lats and lons? I have found that it is often easier to find the
> target point in the coordinate arrays, rather than implementing
> the transformation equations.
>
> This is also a standardized approach where the same search code
> will usually work with any map projection, provided that
> coordinates are included with the data set. HTH.
>
> --Dave
>
>
> On 10/19/2011 7:39 AM, Micah Sklut wrote:
>
> This isn't so much an NCL question, but perhaps someone
> would like
> to help me any way with a lambert conformal question!
>
> If I have a lat/lon, and I want to find the data values of that
> lat/lon in a lambert conformal data set, what equations can
> I use to
> find the x/y coordinates of the data set.
>
> Specifically I am using the NCEP nam data, which has:
> ygrid - 428
> xgrid - 614
> lat-corners - ( 12.19, 14.34209, 57.32843, 54.56534 )
> lon-corners - ( -133.459, -65.12556, -49.416, -152.8786 )
>
> So, if I have a lat/lon, say of 38.5/-98.0, how can i get the
> matching x/y.
>
> I have found some equations, but I am still confused.
> Thanks so much for any suggestions.
>
> --
> Micah Sklut
>
>
>
>
> --
> Micah Sklut
>
>
>
>
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Received on Wed Oct 19 16:58:27 2011