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Re: Get Lat/long equivalent based on NEASE grid value [message #72966 is a reply to message #72964]

Thu, 21 October 2010 12:18

Snow53
Messages: 32
Registered: July 2010

Member

On Oct 21, 1:04 pm, David Fanning <n...@dfanning.com> wrote:
> Snow53 writes:
>> It's the polar version of the NSIDC (http://nsidc.org/data/ease/)
>> grid, based on the Lambert Azimuthal.
>
>> So I've tried to use MAP_PROJ_INIT to define my projection and then
>> feed it into MAP_PROJ_INVERSE to get my lat/long, but I haven't
>> figured out how to point to the NEASE parameters via MAP_PROJ_INIT
>> (AHHH!).
>> I'm assuming that there must be some relatively easy way to do so....
>
> OK, but the NSIDC EASE grid projections use a
> spherical datum, not a WGS-84 datum. Are you
> performing some kind of datum transformation before
> you look for the lat/lon values?
>
> It's relatively easy. You could get the EASE grid
> lat/lon values, for example, from the NSIDC web page. :-)
>
> And if I knew exactly what you are trying to do, I could
> probably provide some code to do it. It would be quite
> easy to do. But I am afraid of what you are going to do
> with these Lambert Azimuthal, WGS-84 lat/lon values and
> NSIDC EASE gridded data. :-)
>
> Cheers,
>
> David
>
> --
> David Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Coyote's Guide to IDL Programming:http://www.dfanning.com/
> Sepore ma de ni thui. ("Perhaps thou speakest truth.")

Hey,

I'm not doing any sort of transformation on the data (WGS-84 was
defined at the datum in the data hdr file I got with these data).

What I want to do is a quick geographic-based masking of these files ,
i.e. anything <50 deg N gets masked as -9999. The way the spherical
NEASE coordinates are set up makes this more difficult to do, so I had
this idea that I would just get the lat/long equivalent and use that
to define the mask criteria (but no easy lunch, right? :) ).

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[Message index]

		Re: Get Lat/long equivalent based on NEASE grid value By: David Fanning on Thu, 21 October 2010 12:46
		Re: Get Lat/long equivalent based on NEASE grid value By: Snow53 on Thu, 21 October 2010 12:33
		Re: Get Lat/long equivalent based on NEASE grid value By: David Fanning on Thu, 21 October 2010 12:28
		Re: Get Lat/long equivalent based on NEASE grid value By: Snow53 on Thu, 21 October 2010 12:18
		Re: Get Lat/long equivalent based on NEASE grid value By: David Fanning on Thu, 21 October 2010 12:04
		Re: Get Lat/long equivalent based on NEASE grid value By: Snow53 on Thu, 21 October 2010 11:50
		Re: Get Lat/long equivalent based on NEASE grid value By: David Fanning on Thu, 21 October 2010 11:39

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