| Re: Help with HDF Format [message #35180 is a reply to message #35177] |
Fri, 16 May 2003 12:01   |
paul wisehart
Messages: 28
Registered: December 2002
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Junior Member |
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On 15 May 2003 13:22:04 -0700, Gautam Bisht <bishtgautam@yahoo.com> wrote:
> I am a new user of IDL and facing trouble trying to open MODIS images
> and its products, which are in HDF and HDF EOS format. I am able to
> see that ENVI can open those files but I want to write a code to
> extract the values in those files. Could someone help me out with
> this? maybe by pointing out some sources where I could get more info.
geov3.pro
ftp://g0dug03u.ecs.nasa.gov/data/modis/tools/hdf/geoview/geo v.pro
ftp://g0dug03u.ecs.nasa.gov/data/modis/tools/hdf/geoview/geo v.pro
http://hdfeos.gsfc.nasa.gov/hdfeos/platforminfo.cfm?ID=32&am p;swID=16
(these should be links to the same thing)
This will let you create an image from L1B1KM, L1BHKM, or L1BQKM files.
Its not easy to create the image unless you know the MODIS hdf format.
Basically if you want a true color image you use either the L1B1KM or
L1BHKM files, and pick bands 1, 4, and 3 (in that order, because they
are appr. Red Green and Blue(or is it Red, Blue, Green?))
Note that band 1 is at 250 meter resolution, and bands 4 & 3 are both
500m resolution. There are different sds data sets for the different
resolutions. (The higher resolution data-sets are included in the
lower resolution hdf files, but they are aggregated to that resolution.)
For example there is band 1(250 m resolution) data ine the L1BHKM
(L1B half-kilometer(500m)) hdf file, but it is represented at the 500m
resolution. This is why you need half or quarter resolution hdf files
to get a true image.
Anyways, the geov3.pro program is all readable IDL code so after you get
it working you can browse thru the code, and see *how* it does what it does.
There are other IDL programs available to read the basic data from L1A files.
If you had a certain data set in mind I could point you in the right
direction.
Post back here if you have any questions.
--
paul \ /
wisehart >/
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paul \ /
wisehart >/
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