CrsKit

A modern C++23 geodesy library for coordinate reference systems, WKT and coordinate transformations.

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CrsKit implements the OGC Coordinate Transformation Services model in modern, portable C++. It reads and writes coordinate reference systems, parses and emits Well-Known Text, and builds and applies transformations between systems, backed by the full EPSG catalogue.

Features

• Coordinate reference systems — geographic 2D/3D, projected, vertical, geocentric and compound, created by EPSG code or from WKT.
• Well-Known Text — parse and emit WKT 1 (OGC and ESRI dialects) and WKT 2 (ISO 19162:2015 and :2019), with grammar auto-detection on parse.
• Coordinate transformations — datum shifts (geocentric / Molodensky-Badekas / Position-Vector / Coordinate-Frame, TOWGS84), map projections, and a large set of grid-based operations: NTv2, NADCON, and geoid models in EGM2008 / EGM96, GeoTIFF (.tif, the PROJ/GDAL format), .gtx, and AUSGeoid (.gsb) — with a self-contained DEFLATE decoder, so the library has no heavy dependencies.
• Conformance-tested — a port of the IOGP GIGS (Geospatial Integrity of Geoscience Software) test series validates the geodesy against the reference dataset.
• Portable and thread-safe — C++23, no MFC or windows.h; builds and passes its tests on Windows (MSVC) and Linux (GCC), and is safe to use from multiple threads.

Using CrsKit (vcpkg)

CrsKit is distributed as a vcpkg registry. Point your project at it in vcpkg-configuration.json:

{
  "registries": [
    {
      "kind": "git",
      "repository": "https://github.com/digi21/crskit",
      "baseline": "<commit of this repo's main>",
      "packages": ["crskit"]
    }
  ]
}

add crskit to your vcpkg.json, and consume it from CMake:

find_package(crskit CONFIG REQUIRED)
target_link_libraries(your_target PRIVATE crskit::crskit)

Using CrsKit from Python

CrsKit has a Python binding (pybind11), published as a wheel:

import crskit

crskit.init("epsg.sqlite")
etrs89 = crskit.crs_from_epsg(4258)      # geographic 2D (latitude, longitude)
utm30n = crskit.crs_from_epsg(25830)     # ETRS89 / UTM zone 30N

crskit.transformation(etrs89, utm30n).transform([40.416775, -3.703790])

It transforms whole NumPy arrays in a single call, emits WKT 1 and WKT 2, compares systems by their mathematical definition, and ships type stubs. There is a tutorial that starts from what a coordinate reference system even is — also in español, français, italiano and deutsch — a reference, and runnable examples.

Building from source

cmake -S . -B build
cmake --build build

The only build inputs are a C++23 compiler and CMake — SQLite is vendored and GoogleTest is fetched automatically. Visual Studio opens the CMakeLists.txt directly (Open Folder), or generate a solution with cmake -G "Visual Studio 17 2022" -B build.

Running the tests

The tests read the EPSG SQLite database, which is not shipped with the source (it is the IOGP EPSG Geodetic Parameter Dataset). Get it either way:

• Download a prebuilt copy from the epsg-data release — epsg-vX.Y.sqlite, named after the EPSG dataset version.
• Build it yourself from the EPSG SQL scripts with tools/epsg-sqlite (see its README) — useful for a newer EPSG version than the one published there.

Then point DIGI21_EPSG_SQLITE at it and run:

DIGI21_EPSG_SQLITE=/path/to/epsg.sqlite ctest --test-dir build --output-on-failure

A few tests need NTv2/geoid grid files that cannot be redistributed (see Data and attribution); they skip or are excluded when the grids are absent.

Data and attribution

CrsKit is the software; the coordinate reference data are supplied separately.

This product uses the EPSG Geodetic Parameter Dataset (https://epsg.org), owned by the International Association of Oil & Gas Producers (IOGP) and used under the EPSG Terms of Use (https://epsg.org/terms-of-use.html). The EPSG Dataset is provided "as is"; IOGP disclaims all warranties as to its accuracy and does not endorse CrsKit. The tools/epsg-sqlite utility builds the SQLite database from the EPSG dataset SQL scripts; an unmodified build is published, for the test suite, in the epsg-data release.

Grid files (geoid models, NTv2 datum-shift grids, …) are not redistributed here — they are obtained by the user from their official sources (national mapping agencies), each under its own licence. data/grid-sources.json maps a grid name to where it can be obtained, so an application can offer to fetch it when the library reports one missing. The global EGM2008 geoid (NGA) is mirrored for convenience at https://digi21.blob.core.windows.net/geodetic-grids/, in the little-endian layout the reader expects.

License

Apache-2.0. See LICENSE.