Changes between Version 1 and Version 2 of FAQ/lev3upsidedown


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Timestamp:
Jul 2, 2009 12:46:31 PM (10 years ago)
Author:
mggr
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  • FAQ/lev3upsidedown

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    7 Flight lines in level 1 data are as the sensor sees them (ie. appearing in the order seen by the sensor).  If the aircraft is flying south, the first lines in the data will be the most northerly with later lines further south.  If the plane is flying east, the first lines will be the most westerly, with later lines heading east.  Navigation data is included with the level 1 imagery and can be used when producing level 3 georeferenced images. You don't need to do any manual rotation to compensate for flight direction yourself when making level 3 images - that's all handled by azgcorr.
     7Flight lines in level 1 data are as the sensor sees them (ie. appearing in the order seen by the sensor).  If the aircraft is flying south, the first lines in the data will be the most northerly with later lines further south.  If the plane is flying east, the first lines will be the most westerly, with later lines heading east.  Navigation data is included with the level 1 imagery and can be used when producing level 3 georeferenced images. You don't need to do any manual rotation to compensate for flight direction yourself when making level 3 images - that's handled by azgcorr.
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    9 Level 3 images are corrected for flight direction and will appear with north up in any viewer that reads the georeferencing information correctly (e.g. ENVI).
     9Level 3 images are corrected for flight direction and will appear with north "up" in any viewer that reads the georeferencing information correctly (e.g. ENVI).
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    11 You'll see the flight lines run south to north in the level 1 data, but when they're processed to level 3 (georectified, via azgcorr), they'll be correctly oriented with north at the top (depending on your viewer, ENVI should be fine).   When it works anyway!
     11If you see level 3 images where "up" is along the flight direction rather than north, this means your viewer hasn't correctly read the georeferencing information.  The most common case is loading the level 3 HDF directly into ENVI.  There is no well defined standard for georeferencing in HDFs so ENVI cannot read the information there and shows data in file order.  To avoid this problem, export the data to a BIL or GeoTIFF file and load that into ENVI instead, e.g.:
     12{{{
     13 # BIL file (recommended)
     14azexhdf -v -h level3_file.hdf -Be level3_file.bil
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    13 If you're still seeing the images upside down when you're looking at level 3 images, let us know what viewer you're using and what file format - this implies you're not getting the georeferencing information correctly.
     16 # GeoTIFF - won't work if filesize > 2GB
     17azexhdf -v -h level3_file.hdf -G level3_file.tif
     18}}}
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    1521[wiki:FAQ Back to FAQ]