Geometries in OGC

This page is about how geometries are currently handled by OGC standards. OGC Standards consider two- and three-dimensional (2D and 3D) geometries. All OGC feature (vector) geometries ultimately are based on the OGC Abstract Specification Topic 1 - Spatial Schema (published as ISO 19107:2019).

Simple Features (2D)

OGC's oldest and most-implemented Standard, Simple Features, describes how to define and encode 2D feature geometries. Simple Features representation is used in all other OGC and similar Standards for feature geometry, including the list below. Simple Features is also the native geometry for geospatial-enabled commercial and open source database systems.

GML (2D and 3D)

As written here, the Geography Markup Language (GML) from OGC is

an XML grammar for expressing geographical features. GML serves as a modeling language for geographic systems as well as an open interchange format for geographic transactions on the Internet. GML is also an ISO standard (ISO 19136:2007).

GeoJSON (2D)

Contrary to some belief, GeoJSON is not authored by OGC but by the IETF. One current limitation of GeoJSON is the fact that it is only handling one coordinate reference system (CRS): EPSG:4326. Yet the big interest of the internet for JSON based format makes it worth considering.

OGC Features and Geometries JSON (2D and 3D)

The work-in-progress OGC Features and Geometries JSON is designed to be the successor of GeoJSON. It is designed such that it can be used in a way that is fully backwards-compatible with GeoJSON. It does this by leaving all fields and structures defined by GeoJSON in place, and only defining new functionality in new fields that do not conflict with existing properties.

OGC Features and Geometries JSON will:

• include the ability to use Coordinate Reference Systems (CRSs) other than WGS84
• follow the OGC Axis Order Policy,
• allow the use of non-Euclidean metrics, in particular ellipsoidal metrics,
• support solids and multi-solids as geometry types, and
• provide guidance on how to represent feature properties, e.g., including temporal properties.

The development of FG-JSON happens on: https://github.com/opengeospatial/ogc-feat-geo-json

Geo3DML (3D)

In Geo3DML: A standard-based exchange format for 3D geological models, the China Geological Survey studied the topic of 3D space geomodels. They proposed extensions of OGC standards are proposed, especially for geometries.

Voxels (3D)

Voxels (or volumetric cells) are a 3D gridded representation of a volume, with attributed values. Voxels can be expressed directly as modeled cubes in Standards such as CityGML or as datacubes represented by coverages or in formats such as HDF5 or Zarr, amongst others.

The concept of gsml:MappedFeature in GeoSciML

The fact that models of the earth and their features can be represented in different way is something well understood and managed in GeoSciML thanks to the concept of MappedFeature that is defined this way:

A MappedFeature is part of a geological interpretation. It provides a link between a notional feature (description package) and one spatial representation of it, or part of it (exposures, surface traces and intercepts, etc.). The mapped features are the elements that compose a map, a cross-section, a borehole log, or any other representation. The mappingFrame identifies the domain being mapped by the geometries. For typical geological maps, the mapping frame is the surface of the earth (the 2.5D interface between the surface of the bedrock and whatever sits on it; atmosphere or overburden material for bedrock maps). It can also be abstract frames, such as the arbitrary plane that forms a mine level or a cross-section, the 3D volume enclosing an ore body or the line that approximate the path of a borehole.