Snaphu export / import take a very long time

Dear all,

I managed to export an Interferogram to SNAPHU format. This step took quite a while: about 40 minutes

The unwrapping process was successfull. It took about one hour to be computed.

I imported the unwrapped phase back to SNAP Toolbox.
The import process took quite a long time too:

  • 1st try, it took more than an hour
  • 2nd try (after computer reboot): about 40 minutes

I am surprised it take so long to import/export to SNAPHU. ProcessExplorer shows that snap.exe is not using my computer resources:

  • CPU = 0.3%
  • I/O : nothing almost 100% of the time

The interferogram is not so large: 27000 X 2900.
Just to check the “data complexity”, I converted some of the raster files from the interferogram with GDAL in just a few seconds.

Thus, I have a few questions:

  • Are there any steps which may take that long?
  • Are there any parameters to tune? I already modified some parameters in Tools=>Options=>Performance (-Xmx15072m, cache size 10550MB)
  • Do you have any hints?

My environment:

  • SSD hard drive
  • RAM: 16 GB
  • Core i7, 8 cores
  • Windows 8
  • SNAP 7.0

Thanks for your help

I agree, but it is far from small either :slight_smile:
But you are right, there must be a bottleneck somewhere else which slows down the import and export.
I experienced similar things, especially large datasets took long (regardless of the actual process of unwrapping)

Sometimes it helps to close SNAP and only load the most recent product. Even if not data is currently being computed, the cache is progressively filled the longer SNAP is open. This is worth a try especially before the import of the unwrapped phase.

The setting of the performance measure -Xmx was reported critical. While for some 80% made most use of the RAM (try 12G) others were more lucky with only 50% (8G in your case).

For the unwrapping itself: Did you select a suitable number of processors (8 in your case) in the config file?

This warrants deeper investigation as that should not happen. Can you share the interferogram in question?

edit: have you installed all the updates to 7.0?

Thank you for your quick answers.

I did two more tests:

  • as Andreas suggested me, I closed SNAP toolbox and reopened it, loading onlyt the interferogram I wanted to export.
    The export step took only 17 minutes instead of 40’ before
  • I also used gpt.exe with an XML script I build, just for SNAPHU export.
    It took 20 seconds !

I believe there are some weird behaviours with the SNAP toolbox GUI. Because it is not usually that long to export/import to SNAPHU. Whatever you do, the application always needs a huge memory chunk.
Could there be some issues around that?

It looks like there is something anomalous going on. If this is related to the setup of your workstation and OS it might be difficult to replicate. @lveci @marpet do you have an idea what could be going on?

Java VM tends to use all the memory allocated to it without releasing it back, unfortunately.