Snaphu export improvements

To avoid memory issues with snaphu, user can tiled the interferogram (e.g. 5 rows and 5 columns with 30 row and col pixels overlapping).

Today, snaphu export module writes the snaphu.conf file with NTILEROW and NTILECOL to 1.

Is it possible to add a tile control ?


To speed up the unwrapping process:

  • tile the interferogram (e.g. 10 x10)
  • thread the process with NPROC (e.g. 4)

There is no guarantee that you can join the tiles together without seeing phase jumps - assume that you cannot.

Before writing this thread, I tested with 10x10, 30x30 tiles and with 4, 6 and 8 parallel processing. It works fine. There is no phase jump: Overlapping parameters do the job (tested with 30 pixels in range and azimuth directions).

I am surprised if this will work in a robust way. A company called tried to implement tiled MCF-type unwrapping for the NEST toolbox and was unfortunately never able to make it function in a robust way. It works for “easy” cases but in more difficult situations the individually unwrapped tiles did not fit together.

edit: we still have the code for this unwrapper if anyone wants to try to make it work!

You’re rights, I’m working on an easy case.

With a S1 dataset more complex, it should work or not ! If you have any S1 pairs more ‘realistic’, I could apply some tests if you want.