Back

SNAP

SNAP

Description

Sentinel Application Platform (SNAP) is a common architecture for all Sentinel Toolboxes.


Available

Version on CSC's Servers

Taito: 7.0-snapshot


Usage

First load appropriate module.

module load snap

Module contains binaries snap, gpt and gpt_array. The snap command launches the GUI for SNAP software and can be used in Taito-shell via NoMachine, although the GUI is not the fastest if multiple files are loaded. Graph Processing Tool gpt is a command line tool used for bulk processing. The gpt_array command is a Taito specific tool that allows using gpt with array jobs using same input file for each job (see below for details).

SNAP Configuration in taito

Snap installation is found in /appl/earth/snap/VERSION and this is where snap.home variable is set to. Default snap.userdir is located at $WRKDIR/DONOTREMOVE/snap-userdir. The reason for having the userdirectory in $WRKDIR instead of the usual $HOME location is that SNAP creates a potentially large cache folder in snap.userdir/var/cache and the home folder is limited to 50GB. While there are more space in work directory than in home location user should ensure that they don't needlessly waste disk space on cache that is not being used.

Running Array jobs

Running SNAP using array jobs is done the same way as for any other software (see here), but when working with same input files for multiple jobs some care needs to be taken because of the SNAP's cache folder. If multiple jobs try to create the cache for same file at the same time this will lead to problems. To ensure that cache is not created by two processes at the same time there are two options:

1) First create the cache and only start the array job as usual after cache has been built. This way the cache doesn't get modified by jobs created in the array job.

2) There exists Taito specific gpt_array command that allows to specify a user directory for an instance of GPT. This can be used to ensure that each job has it's own cache. Usage for gpt_array command: gpt_array userdir normal_gpt_arguments For example to create a separate user directory for each job in an array job script: gpt_array $WRKDIR/tmp_snap_userdir_"$SLURM_ARRAY_TASK_ID" <normal gpt arguments> Note that using -Dsnap.userdir=<dir> with regular gpt command does not work for some reason.

Parallel processing

SNAP supports parallel processing in shared memory environment. This means that you can parallellize SNAP usage within one node in Taito. By default SNAP tries to use however many cores you reserve for it but this can be controlled by user in two ways:

1) Using gpt -q <number_of_cores> allows you to set number of cores you want to use for one instance of GPT.

2) You can also specify the default number of cores to be used in snap.userdir/etc/snap.properties file with line snap.parallelism = <number_of_cores>.

When writing batch job script for GPT you can reserve multiple cores like this:

#SBATCH --cpus-per-task <number_of_cores>
#SBATCH --mem <total amount of shared memory>
#SBATCH --nodes 1
#SBATCH -p serial

Note that while there is up to 16/24 cores available in Taito nodes depending on node type, you should make sure that reserving additional cores actually speeds up the processing.

Plugins

By default following plugins are installed in taito: Sentinel 1,2 and 3 toolboxes and SMOS toolbox. If further plugins are needed contact CSC at servicedesk@csc.fi

SNAPPY Python interface

The snappy Python interface has been installed into a conda environment. It can be loaded with following commands:
module load geoconda snap
source activate snappy6.0

If you would like to use Spyder with snappy,  run the above commands in NoMachine taito-shell terminal and after these spyder. (If you select Spyder in NoMachine mouse menu, then you get access to default geoconda environment, and not snappy.)

 


Discipline

Geosciences

References


Support


Manual

SNAP usage
GPT usage
SNAP configuration