Frequently Asked Questions

This page is designed to complement the Help page. If you ask us one of the questions on this page, you're likely to get an answer copy/pasted from here. If you have read this answer and are still unclear, please mention that you've looked at this page when you contact us so that we don't just give you the same answer again.

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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. Unfortunately azgcorr deals badly with flightlines with significant turns in them (it tends to mess up both interpolation and positioning if the flight goes back on itself at all), which is why that check exists in the first place. There are two solutions to this:

1. (Easy solution) Process the flightline with an extra "-bend" option to azgcorr. 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.

2. (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 1 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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