| Re: Mapping Functionality in IDL 8.1 [message #75722] |
Wed, 13 April 2011 14:24 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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kBob writes:
> Not to take away what David has
> done. I refer to his pages whenever there is a demand for some mapping
> work.
I guess I learned my map projections at the knee of the
"pixels are expensive" purists. I am inheriently suspecious
of image warping and any software that wants me to work in
lat/lon space as opposed to projected meter space. The
combination of the two gives me the shivers. I'm willing
to concede, however, that warping an image to a map
projection may be useful in some cases. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thue. ("Perhaps thos speakest truth.")
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| Re: Mapping Functionality in IDL 8.1 [message #75725 is a reply to message #75722] |
Wed, 13 April 2011 14:04  |
KRDean
Messages: 69
Registered: July 2006
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Member |
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On Apr 12, 5:40 pm, David Fanning <n...@dfanning.com> wrote:
> Folks,
>
> I promised to report back from the IDL User Group
> meeting about the new mapping functionality coming
> in IDL 8.1 (due out in the morning, as I heard it
> today at the meeting).
>
> I'm afraid I don't have much to report. The big
> news is the Map function can now draw a map whose
> boundaries cross the international date line. (An
> outstanding bug in the iTool map object since IDL
> 6.3, when the Map object was introduced.)
>
> The other big mapping news is that that Map object
> can now use the GSHHS database (when the HIRES keyword
> is set) in the MapContinents routine. This is a
> functionality I have been using since 2006 when
> I wrote Map_GSHHS_Shoreline to draw all my shorelines,
> and I highly recommend it.
>
> http://www.idlcoyote.com/map_tips/gshhs.html
>
> I wasn't able to determine if it is the implementation
> of the GSHHS data base that is slow, or if it is the map
> object that is slow, but we waited quite a long time
> after the command was typed to see the result. I've
> never experienced a delay like that with my implementation
> of GSHHS, so I don't know what to think. I am guessing
> they always use the full resolution of the GSHHS database,
> which is almost always unnecessary in practice and does
> take a LONG time to draw. (My routine allows you to choose
> the resolution of the GSHHS database you want to use.)
>
> The biggest problem I see with the Map function is that
> ITTVIS continues to insist that people want to warp an
> image onto a map projection. I've spent a number
> of years working professionally with people who did map
> projections for a living, and I have never once known
> anyone who wanted to do this. Everyone I know HAS an
> image (which they emphatically do NOT want to warp!),
> and they want to fit a map projection onto that.
>
> I'm told to expect more "communication" between the
> ENVI side of ITTVIS and the IDL side. Here is one case
> where listening to the folks who are working with ENVI
> could pay immediate dividends. As it is now, the Map
> function in IDL appears to me to be more toy than tool.
>
> Cheers,
>
> David
>
> --
> David Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Coyote's Guide to IDL Programming:http://www.dfanning.com/
> Sepore ma de ni thue. ("Perhaps thos speakest truth.")
Long ago, I had a request to compare GOES data with NOAA 15 AVHRR. I
warped the GOES data to match the AVHRR projection. No IDL mapping
routines were used in this case. I just used the PolyWarp/Poly2D
combination and my in-house GOES and AVHRR navigation models.
Long ago, before there was MTSAT, there was GMS (Japan geostationary
satellites). Near the end of its life span, imagery from GMS would not
line up with GOES-West due to its wobble. I used PolyWarp/Poly2D so
composites could be made with GOES-West with nice seams between the
two sats.
Currently, I am taking large GeoTIFFs to make one degree cell
composites (coordinates defined by MAP_SET projection). These are done
with PolyWarp/Poly2D and overlay in Direct Graphics. I am looking into
an Object Graphics version.
I was never a fan of IDL's Map_Patch when working with weather
satellite imagery, too slow.
Sorry for bragging about my past accomplishments, but I warped in the
past and plan to warp in the future. Not to take away what David has
done. I refer to his pages whenever there is a demand for some mapping
work.
Kelly Dean
Milliken, CO
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| Re: Mapping Functionality in IDL 8.1 [message #75730 is a reply to message #75725] |
Wed, 13 April 2011 06:48 |
Fabzou
Messages: 76
Registered: November 2010
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Member |
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On 04/13/2011 03:33 PM, Kenneth P. Bowman wrote:
> In article<MPG.280e90ee68f44fe29896fc@news.giganews.com>,
> David Fanning<news@dfanning.com> wrote:
>
>> The biggest problem I see with the Map function is that
>> ITTVIS continues to insist that people want to warp an
>> image onto a map projection. I've spent a number
>> of years working professionally with people who did map
>> projections for a living, and I have never once known
>> anyone who wanted to do this. Everyone I know HAS an
>> image (which they emphatically do NOT want to warp!),
>> and they want to fit a map projection onto that.
>
> The need to warp an image to a map projection may be more common
> than you think. GOES images are a good example. We often have
> gridded data that are in longitude-latitude coordinates. These are
> easy to map (image or contour) using most projections. It can be
> very useful to underlay a GOES image on the map projection.
> MAP_PATCH handles that problem pretty well.
>
> Ken Bowman
Also, MODIS images are not nice to look at in their original sinusoidal
projection.
However, I agree that most of the time, I work in the data native
projection, which is more accurate.
Fab
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| Re: Mapping Functionality in IDL 8.1 [message #75732 is a reply to message #75730] |
Wed, 13 April 2011 06:33 |
Kenneth P. Bowman
Messages: 585
Registered: May 2000
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Senior Member |
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In article <MPG.280e90ee68f44fe29896fc@news.giganews.com>,
David Fanning <news@dfanning.com> wrote:
> The biggest problem I see with the Map function is that
> ITTVIS continues to insist that people want to warp an
> image onto a map projection. I've spent a number
> of years working professionally with people who did map
> projections for a living, and I have never once known
> anyone who wanted to do this. Everyone I know HAS an
> image (which they emphatically do NOT want to warp!),
> and they want to fit a map projection onto that.
The need to warp an image to a map projection may be more common
than you think. GOES images are a good example. We often have
gridded data that are in longitude-latitude coordinates. These are
easy to map (image or contour) using most projections. It can be
very useful to underlay a GOES image on the map projection.
MAP_PATCH handles that problem pretty well.
Ken Bowman
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