| Re: Reprojecting an image file derived from Level 1B MODIS HDF [message #74190] |
Mon, 03 January 2011 06:58  |
liamgumley
Messages: 74
Registered: June 2005
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Member |
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On Jan 2, 5:23 pm, Kasia <sia...@gmail.com> wrote:
> Hi,
>
> I have an image file that I created using IDL from a Level 1B MODIS
> HDF file. I now need to reproject this image file to display in Google
> Earth, but I'm having a hard time figuring out how to do this. The
> code that generated the image file also outputs a lat/lon for each
> value so I thought that would help since there is geographic
> information contained in the image file. But, that hasn't helped me.
>
> I've tried applying the header information from the original HDF file
> to the new image file using ENVI because I know it can read these
> MODIS files, but that hasn't worked too well. ENVI can reproject the
> MODIS HDF file beautifully but I also need it to do the same for the
> new image file.
>
> All of the projection and lat/lon information in the new image file is
> identical to that of the original MODIS HDF file that I can easily
> reproject in ENVI. I just can't figure out how to add that information
> to the image file so ENVI can do the same sort of magic on the new
> file.
>
> Any help would be greatly appreciated!
> Kasia
MRTSwath is an excellent tool for reprojecting MODIS L1B HDF4 swath
data:
https://lpdaac.usgs.gov/lpdaac/tools/modis_reprojection_tool _swath
If I was you, I would go directly from MODIS L1B HDF4 to
equirectangular projection using MRTSwath. This is the projection that
is used by Google Earth. The MRTSwath command line would look
something like this:
swath2grid -if=infile -gf=geofile -of=outfile -oproj="EQRECT" -kk=CC -
osp=8 -opsz=1000 -off=HDF_FMT
where
infile is the MODIS L1B HDF4 swath image file
geofile is the MODIS L1B HDF4 geolocation file
outfile is the reprojected HDF4 file
By default, MRTSwath will reproject all image arrays in the input
file, and store them in the output file.
If you are interested in creating true color MODIS images in tiled
JPEG format for Google Earth, you may wish to check out the "Direct
Broadcast Google Earth" or DBGE package available here:
http://cimss.ssec.wisc.edu/imapp/dbge_v1.2.shtml
DBGE reads MODIS Level 1B data and geolocation, and creates tiled
MODIS true color images at 250 meter resolution, along with the
Keyhole Markup Language (KML) files which allow the imagery to be
displayed in Google Earth. To make the MODIS images and KML files
viewable on the Internet, you will need a web server where the images
and KML files can be stored. It does not have to be the same system
where you run DBGE. Any computer which runs a web server (even a
Windows computer) may be used to serve the images to Google Earth.
The required input data for DBGE are MODIS Level 1B files in NASA HDF4
format:
MODIS Level 1B 1000 meter resolution (MOD021KM/MYD021KM),
MODIS Level 1B 500 meter resolution (MOD02HKM/MYD02HKM),
MODIS Level 1B 250 meter resolution (MOD02QKM/MYD02QKM),
MODIS Level 1B geolocation (MOD03/MYD03).
All four files are required for each granule or overpass of MODIS data
you wish to process with DBGE.
For an example of a real-time web page containing 250m true color
images along with the option to view them in Google Earth, please see
the University of Wisconsin Direct Broadcast MODIS today web page:
http://ge.ssec.wisc.edu/modis-today/
Cheers,
Liam.
Practical IDL Programming
http://www.gumley.com/
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