Version 4 (modified by benj, 7 years ago) (diff)

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Q: When I geocorrect data, Azgcorr stops and complains that the flightline has a turn in it - how can I process my data?

A:
This means that the aircraft turned without turning off the sensor. Azgcorr was designed to process reasonably straight single survey lines and is not intended for use on flights including large turns - attempting to process such lines causes problems. The present default is to continue if a bend is present after giving a warning message; if interpolation selected is -ic (bicubic), -il (linear) or -in (nearest neighbour) the run may fail or leave portions of the line unprocessed.

There are three solutions to this:

  1. (Preferred solution): Process the flightline with an extra "-bend -inf2" option to azgcorr. This will override the turn check and use fast nearest neighbour interpolation, which should be able to handle the turns.
  1. (Secondary solution) If this fails or you don't want nearest neighbour interpolation, process the flightline with an extra "-bend" option to azgcorr (but not -inf2). This will override the turn check and allow processing to proceed. Be aware that this may cause the processing to segfault, and if it doesn't then it may not produce correct positioning. You are advised to check your results against vectors or other known good data.
  1. (Harder solution) Process the flightline in pieces and leave out the bit that's got the bend in it. The easiest way to do this is to process as in 2 above to determine where the bend is on the line, then use the scan line numbers given in the processing run and a bit of trial and error to cut out the bend using the -l option:

azgcorr ... -l <start_line> <end_line> ...

This will geocorrect those parts of the flight between start_line and end_line. If for example you had a flightline that was 20000 lines long and had a bend from lines 7500 - 7900, you'd use two azgcorr commands:

azgcorr ... -l 0 7500 ...
azgcorr ... -l 7900 20000 ...

This would produce two geocorrected images, each with one part of the line.

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