3. Polar2Grid Basics

All of the tools provided by Polar2Grid can be found in the bin directory of the extracted tarball. The majority of the scripts in the software bundle are wrappers around python software.

3.1. Basic Usage

The most common use of Polar2Grid is to convert satellite data files in to gridded image files. In previous versions, this was done primarily through bash shell scripts that explicitly define the reader and writer in the script name. For example,

$POLAR2GRID_HOME/bin/viirs2gtiff.sh -f <path to files>/<list of files>

can be used to create GeoTIFF single band images of all S-NPP VIIRS imager SDR calibrated data with accompnying geolocation files found in <path to files>/<list of files>.

In Version 2.1, we encourage users to migrate to an implementation of Polar2Grid where the reader and writer are defined as arguments to the main polar2grid.sh script. This implementation takes advantage of the modular design of Polar2Grid; a user only needs to decide on a Reader and a Writer and provide them to polar2grid.sh. Creating VIIRS SDR GeoTIFF images from input SDRs using the polar2grid.sh script would look like:

$POLAR2GRID_HOME/bin/polar2grid.sh viirs_sdr gtiff -f <path to files>/<list of files>

Future versions of Polar2Grid will not include support for the individual legacy bash shell scripts. We strongly encourage users to migrate to the polar2grid.sh model. Please see Reader/Writer Combinations for more information.

In Polar2Grid the <path to files> will be searched for the necessary files to make as many products as possible. Similarly if processing errors occur Polar2Grid will attempt to continue processing to make as many products as it can.

For example, executing the following:

$POLAR2GRID_HOME/bin/polar2grid.sh viirs_sdr gtiff -f /home/data/viirs/sdr

will create 8-bit GeoTIFF files of all M-Band, I-Band, and Day/Night Band SDR files it finds in the /home/data/viirs/sdr directory as long as it contains the matching geolocation files. If multiple granules are provided to polar2grid.sh they will be aggregated together. By default the above command resamples the data to a Google Earth compatible Platte Carrée projected grid at ~600m resolution, but this can be changed with command line arguments.

3.2. Common Script Options

Additional command line arguments for the polar2grid.sh script and their defaults are described in the related reader or writer sections. Options that affect remapping are described in the Remapping section. Additionally all Polar2Grid bash scripts accept a -h argument to list all the available command line arguments. Although the available command line arguments may change depending on the reader and writer specified, there are a set of common arguments that are always available:

-h Print detailed helpful information.
--list-products
 List all possible product options to use with -p from the given input data.
-p List of products to create.
-f Input files and paths.
--grid-coverage
 Fraction of grid that must be covered by valid data. Default is 0.1.
-g <grid_name> Specify the output grid to use. Default is the Platte Carrée projection, also known as the wgs84 coordinate system. See Provided Grids and Custom Grids for information on possible values.
--debug Don’t remove intermediate files upon completion.
-v Print detailed log information.

Examples:

polar2grid.sh modis gtiff --list-products -f <path to files>/<list of files>

modis2awips.sh -p vis01 bt20 --grid-coverage=.25 -g 211e -v -f <path to files>

For information on other scripts and features provided by Polar2Grid see the Utility Scripts or Third-Party Recipes sections or the various examples through out the reader and writer sections.

3.3. Reader/Writer Combinations

The table below is a summary of the possible combinations of readers and writers and expectations for the inputs and outputs of polar2grid.sh. To access these features provide the "reader" and "writer" names to the polar2grid.sh script followed by other script options:

$POLAR2GRID_HOME/bin/polar2grid.sh <reader> --list-products <writer> <options> -f /path/to/files

In previous versions of Polar2Grid scripts were all named <reader>2<writer>.sh instead of polar2grid.sh <reader> <writer>. These legacy scripts are still available and still work but the new form of calling is preferred. For example:

$POLAR2GRID_HOME/bin/avhrr2awips.sh <options> -f /path/to/files
Table 3.1 Reader/Writer Summary Table
Input Source Input Filename Pattern Output Type Reader Name Writer Name Legacy Script
Suomi-NPP VIIRS Sensor Data Records SVI01_npp_*.h5 GITCO_npp_*.h5 8-bit single band GeoTIFF viirs_sdr gtiff viirs2gtiff.sh
" " AWIPS NetCDF3 viirs_sdr awips viirs2awips.sh
" " HDF5 viirs_sdr hdf5 viirs2hdf5.sh
" " Binary viirs_sdr binary viirs2binary.sh
" " 24-bit true and false color GeoTIFF crefl gtiff crefl2gtiff.sh
Aqua and Terra MODIS Level 1b (IMAPP or NASA archive files)

MOD021KM*.hdf MOD03*.hdf

or

t1.*1000m.hdf t1.*.geo.hdf

8 bit single band GeoTIFF modis gtiff modis2gtiff.sh
" " AWIPS NetCDF3 modis awips modis2awips.sh
" " HDF5 modis hdf5 modis2hdf5.sh
" " Binary modis binary modis2binary.sh
" " 24-bit true and false color GeoTIFF crefl gtiff crefl2gtiff.sh
NOAA-18, NOAA-19, Metop-A and Metop-B AVHRR AAPP Level 1b hrpt_noaa18_*.l1b 8 bit single band GeoTIFF avhrr gtiff avhrr2gtiff.sh
" " AWIPS NetCDF3 avhrr awips avhrr2awips.sh
" " HDF5 avhrr hdf5 avhrr2hdf5.sh
" " Binary avhrr binary avhrr2binary.sh
GCOM-W1 ASMR2 L1B GW1AM2*L1DLBTBR*.h5 8 bit single band GeoTIFF amsr2_l1b gtiff N/A
" " AWIPS NetCDF3 amsr2_l1b awips N/A
" " HDF5 amsr2_l1b hdf5 N/A
" " Binary amsr2_l1b binary N/A

3.3.1. Creating Your Own Custom Grids

The Polar2Grid software bundle comes with a wrapper script for the Custom Grid Utility for easily creating Polar2Grid grids over a user determined longitude and latitude region. To run it from the software bundle wrapper run:

$POLAR2GRID_HOME/bin/p2g_grid_helper.sh ...

See the script's documentation for more information on how to use this script and the arguments it accepts.