GeographicLib is a small C++ library for: geodesic and rhumb line calculations; conversions between geographic, UTM, UPS, MGRS, geocentric, and local cartesian coordinates; gravity (e.g., EGM2008) and geomagnetic field (e.g., WMM2020) calculations.
SAGA - System for Automated Geoscientific Analyses - is a Geographic Information System (GIS) software with immense capabilities for geodata processing and analysis. SAGA is programmed in the object oriented C++ language and supports the implementation of new functions with a very effective Application Programming Interface (API). Functions are organised as modules in framework independent Module Libraries and can be accessed via SAGA’s Graphical User Interface (GUI) or various scripting...
...Manipulate reconstructions of geological and paleo-geographic features through geological time. Interactively visualize vector, raster and volume data. PyGPlates is the GPlates Pythonlibrary. Get fine-grained access to GPlates functionality in your Python scripts.
OTB is an open-source C++ library for remote sensing images processing
The Orfeo Toolbox is a C++ library for high resolution remote sensing image processing. It is developped by CNES in the frame of the ORFEO program. More information is available at www.orfeo-toolbox.org
It is based on the medical image processing library ITK and offers particular functionalities for remote sensing image processing in general and for high spatial resolution images in particular.
Mapnik is an OpenSource C++/Python toolkit for developing GIS (Geographic Information Systems) applications. At the core is a C++ shared library providing algorithms/patterns for spatial data access and visualization.