Snap - problems related to file opening order (e.g. when calculating indices)

Dear SNAP-developer Team,

I was teaching a class on optical remote sensing last week and (among a bunch of other software) we were using SNAP 6.0 (Desktop implementation version 6.0.5) for a Sentinel-2 data project. The students really appreciated the free software, however, there were a few issues that we would like to report:

In general, we experienced frequent crashes (e.g. when deleting Vector containers) and hang-ups (e.g. options like spatial resampling becoming only available after restarts (NOT in combination with installation of plugins and/or updates), or disappearing pins from the pin manager tool) and or SNAP not reading/displaying products (likely partly to the problem described below).

It may be due to our lack of familiarity with the software but we ran into a lot of trouble due the fact that the order in which files are opened in SNAP is very important with respect to some operations. For example, when calculating spectral indices using the band math > “edit expression” option (which some students did), “$” symbols linking the spectral bands to the order in which their file of origin was opened in the software were automatically included in the expression, linking the resulting index band to the order in which its file of origin was opened. This band (or sometimes the entire file) could then not be opened in a later session (or was blank/could not be displayed - there was no error message). We received an automatic warning when calculating with bands from DIFFERENT files (e.g. pre- and post indices) that there might be issues in the future but not when working with bands from the same file (that is how we figured out what the problem was in the first place).

In addition, the students expressed some ideas/wishes for the future:

  • It would be great if there was a way to see the number of pixels per class (not only percentage). Also, if one could simply assign classes based on (index) thresholds.
  • It would be beneficial to include own labels when exporting lagends

Overall, we are grateful that this free software is being developed and hope our comments it will help to make it run more reliable in the future.