EASE grids: easeconv

EASE-Grid map transformation utilities for IDL. easeconv is version 0.3 and was originally released on December 18, 2013. See the CHANGELOG.md for complete version history.

Level of Support

This repository is fully supported by NSIDC. If you discover any problems or bugs, please submit an Issue. If you would like to contribute to this repository, you may fork the repository and submit a pull request.

See the LICENSE for details on permissions and warranties. Please contact nsidc@nsidc.org for more information.

Requirements

The procedures defined in this directory require the Interactive Data Language (IDL), which requires a license to install and use.

Installation

Please see this documentation for more information on how to install IDL on your system.

Usage

First, cd to the easeconv directory and start an IDL session (idl):

$ cd easeconv/
$ idl
IDL Version 8.3 (linux x86_64 m64). (c) 2013, Exelis Visual Information Solutions, Inc.
Installation number: xxx-xxxx.
Licensed for use by: University of Colorado - Boulder (MAIN)

IDL>

Next, compile easeconv.pro with the .RUN command:

IDL> .RUN easeconv.pro
% Compiled module: SSMI_CONVERT.
% Compiled module: SSMI_INVERSE.
% Compiled module: EASE_CONVERT.
% Compiled module: EASE_INVERSE.

NOTE: if you get a 'file not found' or 'Variable is undefined' error, make sure you are in the easeconv directory before compiling easeconv.pro!

Two main functions are defined exposed by compiling easeconv.pro: ease_convert and ease_inverse. All other functions are support routines for these top-level functions.

ease_convert and ease_inverse perform forward ((lat,lon) to (col,row)) and inverse ((col,row) to (lat,lon)) transformations respectively for all of the supported original (spherical) EASE-Grids and the currently supported (wgs84 ellipsoid) EASE-Grid-2.0 grids.

• Supported original (spherical) EASE-Grids:
  • SSM/I Polar Pathfinder: [NSM][lh] (where l="low" res (25km), h="high" res (12.5km))
  • AVHRR Polar Pathfinder: [NS]a{1,5,25} (where 1=1.25 km res, 5=5 km res, 25=25 km res)
  • TOVS-P Polar Pathfinder: NpathP (100km res)
  • AARI sea ice: AARI or (equivalent) NAARI (12.5 km res)
  • MODIS sea ice: [NS]Modis[14]km
• Supported (WGS84) EASE-Grid-2.0 grids:
  • Grid names according to the pattern "EASE2_pxx" where: p = projection: 'N' (north), 'S' (south), 'M' (cylindrical) xx - resolution: '25km', '12.5km', '6.25km', '36km', '09km', '03km', '01km' for all projections, and '100km' (for N projection only) Example: EASE2_M25km, EASE2_M09km, etc.

ease_convert

The ease_convert function performs forward transformations from (lat, lon) to (col, row).

IDL> grid_name = 'Nl'
IDL> latitude = 80
IDL> longitude = -120
IDL> status = ease_convert(grid_name, latitude, longitude, r, s)
% Compiled module: EASECONV_DEG2RAD.
% Compiled module: EASECONV_NORMALIZE_DEGREES.
IDL> print, status, r, s
       0       321.63207       337.84827

ease_inverse

The ease_inverse function performs inverse transformations from (col,row) to (lat,lon).

IDL> grid_name = 'Nl'
IDL> r = 321.63
IDL> s = 337.85
IDL> status = ease_inverse(grid_name, r, s, lat, lon)
% Compiled module: EASECONV_RAD2DEG.
IDL> print, status, lat, lon
       0       79.999791      -119.99672

License

See LICENSE.

Code of Conduct

See Code of Conduct.

Credit

This software was developed by the NASA National Snow and Ice Data Center Distributed Active Archive Center.

Author: M.J. Brodzik, 2013