Geographic coordinate transformations are used in many applications at the National Snow & Ice Data Center, including gridded data display tools, data processing systems, and online area search interfaces. These applications require accurate, efficient, and reusable transformation routines. The common packages GCTP and PROJ were difficult to use in our modern multi-threaded event driven software architectures. The mapx library was developed to fill this gap for our internal uses. We are now offering the library to outside users.
The main benefit of an object-oriented design for the mapping library is that each transformation is independent. Often, in the available standard packages, only one instance of a given projection can be initialized at a time. In mapx the creation and initialization of a new transformation has no effect on existing mapx objects. This is an important feature where concurrent processing is required. Examples include simultaneously ingesting data from different maps, pixel-by-pixel conversion of one map to another, or an online map server with multiple projection options.
The following projections are currently implemented:
- Azimuthal_Equal_Area
- Cylindrical_Equal_Area
- Mercator
- Mollweide
- Orthographic
- Sinusoidal
- Cylindrical_Equidistant
- Polar_Stereographic
- Polar_Stereographic_Ellipsoid
- Azimuthal_Equal_Area_Ellipsoid
- Cylindrical_Equal_Area_Ellipsoid
- Lambert_Conic_Conformal_Ellipsoid
- Interupted_Homolosine_Equal_Area
- Albers_Conic_Equal_Area
- Albers_Conic_Equal_Area_Ellipsoid
- Integerized_Sinusoidal
- Transverse_Mercator
- Transverse_Mercator_Ellipsoid
- Universal_Transverse_Mercator
- or anything reasonably similar
And, the library's design makes it easy to add new projections.
Many projections have both spherical and ellipsoidal versions. The initialization of each transformation allows for the use of a different datum to describe the spheroid. Even two transformations with the same projection can have different datums. The datum is not restricted to the Earth. You could easily use mapx on the moon or Mars, for example.
The coordinate transformations used in mapx are (for the most part) taken from Snyder and tested against the numerical examples he gives in Appendix A. Further, all transformations are tested against their inverse and are consistent to within one meter.
This is the C version of the library. There is also a Java version available at http://nsidc.org/data/tools/
Both versions provide constructors, a destructor, a forward transformation (from latitude and longitude to map coordinates), an inverse transformation (map coordinates to latitude and longitude), and a test to determine if a point is within a map.
In addition the C version has a derived grid object that abstracts a map projection and a matrix object for the storage and retrieval of gridded data.
There are also a couple of two dimensional modeling objects--a polynomial based model called pmodel and a cubic spline based model called smodel.
And, finally, an interface to a coastlines database derived from a combination of WDBII and World Vector Shoreline.
This package also contains several standalone routines that serve as test beds and coding examples but also as useful applications in their own right. Some examples include:
- gridloc - output latitude and longitude for every cell in a grid
- regrid - interpolate data from one grid to another
- resamp - interpolate data from one grid to another (in a slightly different way)
- irregrid - interpolate irregularly sampled data (points) to a grid
- mapenum - enumerate (list) map feature vectors from a cdb file
- mtest - interactive command line map transformations
- gtest - interactive command line grid transformations
Snyder, John P., Map Projections Used by the U.S. Geological Survey, 1982.
- This repository is not actively supported by NSIDC but we welcome issue submissions and pull requests in order to foster community contribution.
See the LICENSE for details on permissions and warranties. Please contact [email protected] for more information.
This package requires:
- C Compiler
See the INSTALL file for details on installing the library and tools.
Describe how to use the MyRepository application/tool, with platform-specific instructions if necessary.
Describe any tips or tricks in case the user runs into problems.
The mapx library is open source software. You can redistribute it and/or modify it under the terms of the GNU Lesser General Public License (LGPL) as published by the Free Software Foundation.
THE SOFTWARE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. THE UNIVERSITY DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. See the GNU LGPL for more details.
See LICENSE.
See Code of Conduct.
This software was developed by the National Snow and Ice Data Center with funding from multiple sources.
Copyright (C) 1990-2004 University of Colorado.