SNAP (Sentinel Application Platform) is a remote sensing toolbox architecture developed by the European Space Agency. It includes tools for all common satellite platforms.
SNAP is available in Puhti with following versions:
- 9.0 (without Python interfaces)
- 8.0 (Singularity container with snappy 8.0.3 and Python 3.6.9)
- Sentinel toolboxes (1,2,3)
- SMOS toolbox
- Radarsat toolbox
- PROBA-V toolbox
You can install more plugins to your own user directory from the SNAP Graphical user interface.
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.
- Log in to Puhti web interface. Puhti web interface documentation.
- Start SNAP: Apps -> Desktop, choose Desktop: 'single application' and App: 'SNAP'
- 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:
- Log in to Puhti web interface.
- Open Remote desktop: Apps -> Desktop, choose Desktop:
- 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.
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
-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 examples for Puhti
- Full examples how to run GPT in Puhti in GitHub. The examples include both a simple job with one GPT graph and an array job where the same graph is computed for several input images.
Using SNAP with the Python library snappy
It is also possible to access SNAP functionalities from Python with the snappy library.
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
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".
- SNAP homepage
- SNAP CSC example
- SNAP command line tutorial (GPT)
- SNAP wiki
- SNAP tutorials
- snappy Python examples
- Creating a GPF Graph
- Bulk Processing with GPT command