PROJ is a standard UNIX filter function which converts geographic longitude and latitude coordinates into cartesian coordinates (and vice versa), and it is a C API for software developers to include coordinate transformation in their own software. PROJ is maintained on GitHub.



The projects.h header and the functions related to it is considered deprecated from version 5.0.0 and onwards. The header will be removed from PROJ in version 6.0.0 scheduled for release February 1st 2019.


The nmake build system on Windows will not be supported from version 6.0.0 on onwards. Use CMake instead.


The proj_api.h header and the functions related to it is considered deprecated from version 5.0.0 and onwards. The header will be removed from PROJ in version 7.0.0 scheduled for release February 1st 2020.


With the introduction of PROJ 5, behavioural changes has been made to existing functionality. Consult Known differences between versions for the details.

PROJ 5.0.1

March 1st 2018

Bug fixes

  • Handle ellipsoid change correctly in pipelines when +towgs84=0,0,0 is set (#881)

  • Handle the case where nad_ctable2_init returns NULL (#883)

  • Avoid shadowed declaration errors with old gcc (#880)

  • Expand +datum properly in pipelines (#872)

  • Fail gracefully when incorrect headers are encountered in grid files (#875)

  • Improve roundtrip stability in pipelines using +towgs84 (#871)

  • Fixed typo in gie error codes (#861)

  • Numerical stability fixes to the geodesic package (#826 & #843)

  • Make sure that transient errors are returned correctly (#857)

  • Make sure that locally installed header files are not used when building PROJ (#849)

  • Fix inconsistent parameter names in proj.h/proj_4D_api.c (#842)

  • Make sure +vunits is applied (#833)

  • Fix incorrect Web Mercator transformations (#834)

PROJ 5.0.0

February 1st 2018

This version of PROJ introduces some significant extensions and improvements to (primarily) the geodetic functionality of the system.

The main driver for introducing the new features is the emergence of dynamic reference frames, the increasing use of high accuracy GNSS, and the related growing demand for accurate coordinate transformations. While older versions of PROJ included some geodetic functionality, the new framework lays the foundation for turning PROJ into a generic geospatial coordinate transformation engine.

The core of the library is still the well established projection code. The new functionality is primarily exposed in a new programming interface and a new command line utility, cct (for “Coordinate Conversion and Transformation”). The old programming interface is still available and can - to some extent - use the new geodetic transformation features.

The internal architecture has also seen many changes and much improvement. So far, these improvements respect the existing programming interface. But the process has revealed a need to simplify and reduce the code base, in order to support sustained active development.

Therefore we have scheduled regular releases over the coming years which will gradually remove the old programming interface.

This will cause breaking changes with the next two major version releases, which will affect all projects that depend on PROJ (cf. section “deprecations” below).

The decision to break the existing API has not been easy, but has ultimately been deemed necessary to ensure the long term survival of the project. Not only by improving the maintainability immensely, but also by extending the potential user (and hence developer) community.

The end goal is to deliver a generic coordinate transformation software package with a clean and concise code base appealing to both users and developers.

Versioning and naming

For the first time in more than 25 years the major version number of the software is changed. The decision to do this is based on the many new features and new API. While backwards compatibility remains - except in a few rare corner cases - the addition of a new and improved programming interface warrants a new major release.

The new major version number unfortunately leaves the project in a bit of a conundrum regarding the name. For the majority of the life-time of the product it has been known as PROJ.4, but since we have now reached version 5 the name is no longer aligned with the version number.

Hence we have decided to decouple the name from the version number and from this version and onwards the product will simply be called PROJ.

In recognition of the history of the software we are keeping PROJ.4 as the name of the organizing project. The same project team also produces the datum-grid package.

In summary:

  • The PROJ.4 project provides the product PROJ, which is now at version 5.0.0.

  • The foundational component of PROJ is the library libproj.

  • Other PROJ components include the application proj, which provides a command line interface to libproj.

  • The PROJ.4 project also distributes the datum-grid package, which at the time of writing is at version 1.6.0.


  • Introduced new API in proj.h.

    • The new API is orthogonal to the existing proj_api.h API and the internally used projects.h API.

    • The new API adds the ability to transform spatiotemporal (4D) coordinates.

    • Functions in the new API use the proj_ namespace.

    • Data types in the new API use the PJ_ namespace.

  • Introduced the concept of “transformation pipelines” that makes possible to do complex geodetic transformations of coordinates by daisy chaining simple coordinate operations.

  • Introduced cct, the Coordinate Conversion and Transformation application.

  • Introduced gie, the Geospatial Integrity Investigation Environment.

    • Selftest invoked by -C flag in proj has been removed

    • Ported approx. 1300 built-in selftests to gie format

    • Ported approx. 1000 tests from the gigs test framework

    • Added approx. 200 new tests

  • Adopted terminology from the OGC/ISO-19100 geospatial standards series. Key definitions are:

    • At the most generic level, a coordinate operation is a change of coordinates, based on a one-to-one relationship, from one coordinate reference system to another.

    • A transformation is a coordinate operation in which the two coordinate reference systems are based on different datums, e.g. a change from a global reference frame to a regional frame.

    • A conversion is a coordinate operation in which both coordinate reference systems are based on the same datum, e.g. change of units of coordinates.

    • A projection is a coordinate conversion from an ellipsoidal coordinate system to a plane. Although projections are simply conversions according to the standard, they are treated as separate entities in PROJ as they make up the vast majority of operations in the library.

  • New operations

  • Significant documentation updates, including

    • Overhaul of the structure of the documentation

    • A better introduction to the use of PROJ

    • A complete reference to the new API

    • a complete rewrite of the section on geodesic calculations

    • Figures for all projections

  • New “free format” option for operation definitions, which permits separating tokens by whitespace when specifying key/value- pairs, e.g. proj = merc lat_0 = 45.

  • Added metadata to init-files that can be read with the proj_init_info() function in the new proj.h API.

  • Added ITRF2000, ITRF2008 and ITRF2014 init-files with ITRF transformation parameters, including plate motion model parameters.

  • Added ellipsoid parameters for GSK2011, PZ90 and “danish”. The latter is similar to the already supported andrae ellipsoid, but has a slightly different semimajor axis.

  • Added Copenhagen prime meridian.

  • Updated EPSG database to version 9.2.0.

  • Geodesic library updated to version 1.49.2-c.

  • Support for analytical partial derivatives has been removed.

  • Improved performance in Winkel Tripel and Aitoff.

  • Introduced pj_has_inverse() function to proj_api.h. Checks if an operation has an inverse. Use this instead of checking whether P->inv exists, since that can no longer be relied on.

  • ABI version number updated to 13:0:0.

  • Removed support for Windows CE.

  • Removed the VB6 COM interface.

Bug fixes

  • Fixed incorrect convergence calculation in Lambert Conformal Conic. (#16)

  • Handle ellipsoid parameters correctly when using +nadgrids=@null. (#22)

  • Return correct latitude when using negative northings in Transverse Mercator. (#138)

  • Return correct result at origin in inverse Mod. Stereographic of Alaska. (#161)

  • Return correct result at origin in inverse Mod. Stereographic of 48 U.S. (#162)

  • Return correct result at origin in inverse Mod. Stereographic of 50 U.S. (#163)

  • Return correct result at origin in inverse Lee Oblated Stereographic. (#164)

  • Return correct result at origin in inverse Miller Oblated Stereographic. (#165)

  • Fixed scaling and wrap-around issues in Oblique Cylindrical Equal Area. (#166)

  • Corrected a coefficient error in inverse Transverse Mercator. (#174)

  • Respect -r flag when calling proj with -V. (#184)

  • Remove multiplication by 2 at the equator error in Stereographic projection. (#194)

  • Allow +alpha=0 and +gamma=0 when using Oblique Mercator. (#195)

  • Return correct result of inverse Oblique Mercator when alpha is between 90 and 270. (#331)

  • Avoid segmentation fault when accessing point outside grid. (#396)

  • Avoid segmentation fault on NaN input in Robin inverse. (#463)

  • Very verbose use of proj (-V) on Windows is fixed. (#484)

  • Fixed memory leak in General Oblique Transformation. (#497)

  • Equations for meridian convergence and partial derivatives have been corrected for non-conformal projections. (#526)

  • Fixed scaling of cartesian coordinates in pj_transform(). (#726)

  • Additional bug fixes courtesy of Google’s OSS-Fuzz program