GeOS

GEOS, or Geometry Engine - Open Source, is a portable C++ library that provides spatial predicates and overlay operations for two-dimensional geometries. It is a C++ port of the Java Topology Suite (JTS) and is maintained by the Open Source Geospatial Foundation (OSGeo) community. The library supplies the core geometric algorithms used by many GIS applications to perform spatial questions and operations in a robust, reliable manner.

GEOS exposes a range of functionality for planar geometries, including spatial predicates such as intersects, contains, within, crosses, overlaps, touches, and equals, as well as overlay operations like intersection, union, difference, and symmetric difference. It also offers basic geometry utilities such as distance, length, area, and centroid calculations. The library is designed to be used by host applications to implement high-level GIS processing, handling the intricacies of geometric validity and robustness in 2D space.

Interfaces and usage considerations are broad: GEOS provides both C++ and C interfaces (via a C wrapper) to enable integration with a variety of programming languages. Geometries can be read and written in standard formats like WKT and WKB within the host software, and the library is compatible with common GIS toolchains and data formats. GEOS is cross-platform and widely adopted in the GIS ecosystem, playing a core role in projects such as PostGIS, QGIS, MapServer, and GDAL/OGR for spatial analysis and data processing.

GeOS remains under active development by the OSGeo community to improve performance, robustness, and interoperability with other spatial data tools.