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SNAP

SNAP (Sentinel Application Platform) is a remote sensing toolbox architecture developed by the European Space Agency. It includes tools for all common remote sensing satellites.

Available

SNAP is available in Puhti with following versions:

  • 8.0 (Singularity container with snappy 8.0.3 and Python 3.6.9)
  • 7.0 (with snappy 6.0 and python 2.7.5)

Installed plugins

  • Sentinel toolboxes (1,2,3)
  • All Idepix processors (only in 7.0)
  • SMOS toolbox
  • SNAPHU (only in 7.0)
  • Radarsat toolbox
  • PROBA-V toolbox
  • Sen2Cor (external tool) (only in 7.0)

You can install more plugins to your user directory from the SNAP Graphical user interface

Usage

SNAP is included in the snap module and can be loaded with:

module load snap

This loads the newest available version. You can load an older version with:

module load snap/<VERSION>

Using SNAP with Graphical User Interface (GUI) in Puhti web interface

The easiest option for using SNAP is to open it in Puhti web interface as Desktop app.

  1. Log in to Puhti web interface. Puhti web interface documentation.
  2. Start SNAP: Apps -> Desktop, choose Desktop: 'single application' and App: 'SNAP'
  3. The SNAP GUI is started automatically when the Desktop is launched.

Alternatively, especially if you want to use SNAP together with some other GUI tool, want to user older version of SNAP or want to increase the default Java memory allocaiton, SNAP can be started in Puhti web interface with remote desktop:

  1. Log in to Puhti web interface.
  2. Open Remote desktop: Apps -> Desktop, choose Desktop: mate or xfce.
  3. After launcing the remote desktop, double-click SNAP icon OR open Host Terminal (Desktop icon) and start SNAP:
module load snap
source snap_add_userdir $TMPDIR
snap -J-xmx10G

SNAP userdir and Java temp dir configuration

SNAP uses significant amount of storage space for cache and temporary files. By default these are written to your HOME directory and may easily fill your HOME. For avoiding that configure your snap user directory and Java temporary folder. You should run this script every time you start using SNAP in Puhti or want to change the used folders.

After loading the snap module run

source snap_add_userdir <YOUR-PROJECTS-SCRATCH-FOLDER>

You could also request a fast nvme disk in a batch job and run the command first in the batch job so that all the temp/cache files are written to a fast disk rather than the scratch. It might provide speed improvement in demanding calculations.

source snap_add_userdir $LOCAL_SCRATCH with batch jobs

source snap_add_userdir $TMPDIR with interactive jobs

This scripts sets also Java temporary folder, it is set to be snap/temp subfolder in the folder you defined. If you want to set Java temporary folder to be somewhere else use: export _JAVA_OPTIONS="$_JAVA_OPTIONS -Djava.io.tmpdir=<SOME-FOLDER>" after setting the user directory.

Note

The graphical user interface does not follow snap.userdir setting, but it notices the Java setting. Using SNAP GUI will create a .snap folder inside your HOME directory and fill it. Empty it if you run out of space in your HOME directory.

Java memory settings

By default SNAP/8.0 in Puhti uses only up to 2 Gb memory for Java. To increase this, add -J-xmx10G or similar setting to snap or gpt command. -J-xmx10G extends the Java maximum memory to 10Gb. Adjust this according to your needs and job memory reservation. Compared to your job memory reservation use for Java a few Gb less.

Using SNAP with Graph Processing Tool (gpt) command

The Graph Processing Tool gpt is a command line tool used for bulk processing. Using GPT more computing power can be used than with SNAP graphical interface, because it can be used in scripts and therefore included in jobs that can be submitted to any Puhti partition.

GPT command looks often something like this:

gpt -J-xmx10G <full_path_to_graph_xml_file> -Pfile=<inputfile> -t <outputfile>

Some relevant gpt options include:

  • -J-xmx10G maximum memory used by Java.
  • -q Number of threads the gpt instance will use. Set it to the number of CPU cores requested or more
  • -c Cache size in bytes. Change this if storage space becomes an issue
  • -x Clear internal tile cache after writing a complete row of tiles to output file. Add this if memory becomes an issue

See the links under references at the end of this page for additional info about GPT.

Also the following command is very useful in creating the graphs for different operators. It can be executed in an interactive session 

sinteractive -i
module load snap
gpt <snap-operator> -h

gpt --diag -J-Xmx60G -c 40G can be used to see which memory and cache settings are used by gpt.

GPT examples for Puhti

Using SNAP with the Python library snappy

It is also possible to access SNAP functionalities from Python with the snappy library.

SNAP 8.0

Running snappy scripts with batch jobs: 

singularity_wrapper exec python3 <YOUR-PYTHON-SCRIPT>

See available packages: 

singularity_wrapper exec pip list

Installing new packages to your HOME directory, see Python instructions how to change installation directory.

singularity_wrapper exec pip <NEW-PACKAGE-NAME> --user

License and acknowledgement

All SNAP software is published under the GPL-3 license and its sources are available on GitHub.

Please acknowledge CSC and Geoportti in your publications, it is important for project continuation and funding reports. As an example, you can write "The authors wish to thank CSC - IT Center for Science, Finland (urn:nbn:fi:research-infras-2016072531) and the Open Geospatial Information Infrastructure for Research (Geoportti, urn:nbn:fi:research-infras-2016072513) for computational resources and support".

References

Last update: May 31, 2022