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Snow53...
Posted: Thu Oct 21, 2010 6:23 pm
 
Hi all,


I have a file whose coordinate is in WGS-84 NEASE grid. I would like
to determine the lat/long value for each input pixel location. I
don't want to actually re-project the file, I just want that value. I
have included NEASE in the ENVI map_proj.txt file.

Any suggestions as to what might be the best way to do this?

Thanks!
 
Snow53...
Posted: Thu Oct 21, 2010 6:50 pm
 
On Oct 21, 12:39 pm, David Fanning <n... at (no spam) dfanning.com> wrote:
Quote:
Snow53 writes:
I have a file whose coordinate is in WGS-84 NEASE grid.   I would like
to determine the lat/long value for each input pixel location.  I
don't want to actually re-project the file, I just want that value.  I
have included NEASE in the ENVI map_proj.txt file.

Any suggestions as to what might be the best way to do this?

What in the world is a NEASE grid? :-)

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.")

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....
 
Snow53...
Posted: Thu Oct 21, 2010 7:18 pm
 
On Oct 21, 1:04 pm, David Fanning <n... at (no spam) dfanning.com> wrote:
Quote:
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? Smile ).
 
Snow53...
Posted: Thu Oct 21, 2010 7:33 pm
 
On Oct 21, 1:28 pm, David Fanning <n... at (no spam) dfanning.com> wrote:
Quote:
Snow53 writes:
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? Smile  ).

Well out of the realm of my expertise now. :-)

You can probably locate the files you need here:

   http://nsidc.org/data/ease/tools.html

The errors you introduce with a WGS-84 datum are small
compared to what you want to use it for. :-)

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.")

Thanks David.
 
David Fanning...
Posted: Thu Oct 21, 2010 10:39 pm
 
Snow53 writes:

Quote:
I have a file whose coordinate is in WGS-84 NEASE grid. I would like
to determine the lat/long value for each input pixel location. I
don't want to actually re-project the file, I just want that value. I
have included NEASE in the ENVI map_proj.txt file.

Any suggestions as to what might be the best way to do this?

What in the world is a NEASE grid? :-)

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.")
 
David Fanning...
Posted: Thu Oct 21, 2010 11:04 pm
 
Snow53 writes:

Quote:
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.")
 
David Fanning...
Posted: Thu Oct 21, 2010 11:28 pm
 
Snow53 writes:

Quote:
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? Smile ).

Well out of the realm of my expertise now. :-)

You can probably locate the files you need here:

http://nsidc.org/data/ease/tools.html

The errors you introduce with a WGS-84 datum are small
compared to what you want to use it for. :-)

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.")
 
David Fanning...
Posted: Thu Oct 21, 2010 11:46 pm
 
Snow53 writes:

Quote:
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....

By the way, I was going to write in one of my answers that
you can't use MAP_PROJ_INIT to create a Lambert Azimuthal
Equal Area (EASE grid) with a WGS-84 datum anyway, since
you can't use non-spherical axes to define your datum with
this projection. But, of course, I looked at the IDL on-line
help before I posted this, which is part of my strategy to
avoid looking the fool.

It said you could! That confused me, so I looked at the IDL
7 on-line help just now. That said you couldn't!

So, hooray! Something I really need is FIXED in IDL 8.0!!
I *knew* there was a reason I was spending all that money
to upgrade. ;-)

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.")
 
 
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