PROJ — The Complete Guide: Open-Source Coordinate Transformation and Map Projections
PROJ is the quiet component working behind the scenes every time QGIS or GDAL converts a layer from one coordinate system to another. You can also use it directly, from the command line, to convert point files accurately and see exactly what happens in the transformation.
PROJ
PROJ contributors (OSGeo)
Coordinate transformation software between reference systems and map projections, with command-line tools such as cs2cs and projinfo.
Get it from the vendorWhat you get
- cs2cs — conversion between any two coordinate systems, including datum shifts.
- projinfo — shows system definitions and the possible transformation pipelines between them.
- cct — four-dimensional transformations, including a time component.
- geod — geodesic distance and azimuth calculations on the ellipsoid.
- projsync — downloads correction grid files for higher accuracy.
A tip for surveyors and engineers
When two layers are off by a few metres, the cause is usually a different datum transformation. Running projinfo on both systems lists the available pipelines and the accuracy of each. There is no graphical interface, and the project distributes source code only — ready-made binaries come through OSGeo4W, conda, Homebrew or Linux package managers.
Related tools
To convert whole files between formats and systems — GDAL. To work graphically with layers in different systems — QGIS. For a quick single-point conversion in the browser — Earth Point.
GDAL
OSGeo
Command-line tools and a library to convert, reproject, clip and process geodata — DEMs, GeoTIFF, Shapefile and more.
Get it from the vendor
QGIS
QGIS.org
Open-source GIS for spatial analysis, layer work and map production.
Get it from the vendor
Earth Point — coordinate converter
Earth Point
Converts between coordinate systems and shows the point on a map.
Get it from the vendor
GRASS GIS
OSGeo
GIS with strong raster and terrain analysis — catchments, slope, visibility and elevation models.
Get it from the vendorThe bottom line
PROJ is basic infrastructure for any work with coordinates. Even those who never run it directly benefit from understanding it when conversions do not line up.