| Re: Get Lat/long equivalent based on NEASE grid value [message #72961] |
Thu, 21 October 2010 12:46 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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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....
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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| Re: Get Lat/long equivalent based on NEASE grid value [message #72963 is a reply to message #72961] |
Thu, 21 October 2010 12:33  |
Snow53
Messages: 32
Registered: July 2010
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Member |
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On Oct 21, 1:28 pm, David Fanning <n...@dfanning.com> wrote:
> 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? :) ).
>
> 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.
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| Re: Get Lat/long equivalent based on NEASE grid value [message #72964 is a reply to message #72963] |
Thu, 21 October 2010 12:28 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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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? :) ).
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.")
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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
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Member |
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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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| Re: Get Lat/long equivalent based on NEASE grid value [message #72967 is a reply to message #72966] |
Thu, 21 October 2010 12:04 |
David Fanning
Messages: 11724
Registered: August 2001
|
Senior Member |
|
|
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.")
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| Re: Get Lat/long equivalent based on NEASE grid value [message #72968 is a reply to message #72967] |
Thu, 21 October 2010 11:50 |
Snow53
Messages: 32
Registered: July 2010
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Member |
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On Oct 21, 12:39 pm, David Fanning <n...@dfanning.com> wrote:
> 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....
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| Re: Get Lat/long equivalent based on NEASE grid value [message #72969 is a reply to message #72968] |
Thu, 21 October 2010 11:39 |
David Fanning
Messages: 11724
Registered: August 2001
|
Senior Member |
|
|
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.")
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