CityGML is an open standardised data model and exchange format to store digital 3D models of cities and landscapes. It defines ways to describe most of the common 3D features and objects found in cities (such as buildings, roads, rivers, bridges, vegetation and city furniture) and the relationships between them. It also defines different standard levels of detail (LoDs) for the 3D objects, which allows the representation of objects for different applications and purposes, such as simulations, urban data mining, facility management, and thematic inquiries.
CityGML is implemented as a GML application schema for the Geography Markup Language 3 (GML3), the extendible international standard for spatial data exchange issued by the Open Geospatial Consortium (OGC) and the ISO TC211.
In its most common implementation, which is the one generally used to disseminate and exchange data, CityGML datasets consist of a set of XML files and possibly some accompanying image files that are used as textures. Each text file can represent a part of the dataset, such as a specific region, a specific type of object (such as a set of roads), or a predefined LoD. The structure of a CityGML file is a hierarchy that ultimately reaches down to individual objects and their attributes. These objects have a geometry that is described using GML.
Another important implementation of CityGML is the one of 3D City DB, which stores CityGML in a database. [1]
The OGC Members adopted version 1.0.0 of CityGML as an official OGC Standard in August 2008. [2] In late 2011, the OGC Members approved version CityGML 2.0.0. CityGML 3.0 GML Encoding Specification is supposed to be published early 2019, [3] while CityGML 3.0 Conceptual Model draft is already publicly available at the official Github repository.
The Geography Markup Language (GML) is the XML grammar defined by the Open Geospatial Consortium (OGC) to express geographical features. GML serves as a modeling language for geographic systems as well as an open interchange format for geographic transactions on the Internet. Key to GML's utility is its ability to integrate all forms of geographic information, including not only conventional "vector" or discrete objects, but coverages and sensor data.
A coverage is the digital representation of some spatio-temporal phenomenon. ISO 19123 provides the definition:
In computing, the Open Geospatial Consortium Web Feature Service (WFS) Interface Standard provides an interface allowing requests for geographical features across the web using platform-independent calls. One can think of geographical features as the "source code" behind a map, whereas the WMS interface or online tiled mapping portals like Google Maps return only an image, which end-users cannot edit or spatially analyze. The XML-based GML furnishes the default payload-encoding for transporting geographic features, but other formats like shapefiles can also serve for transport. In early 2006 the OGC members approved the OpenGIS GML Simple Features Profile. This profile is designed both to increase interoperability between WFS servers and to improve the ease of implementation of the WFS standard.
A GIS file format is a standard for encoding geographical information into a computer file, as a specialized type of file format for use in geographic information systems (GIS) and other geospatial applications. Since the 1970s, dozens of formats have been created based on various data models for various purposes. They have been created by government mapping agencies, GIS software vendors, standards bodies such as the Open Geospatial Consortium, informal user communities, and even individual developers.
GeoTIFF is a public domain metadata standard which allows georeferencing information to be embedded within a TIFF file. The potential additional information includes map projection, coordinate systems, ellipsoids, datums, and everything else necessary to establish the exact spatial reference for the file. The GeoTIFF format is fully compliant with TIFF 6.0, so software incapable of reading and interpreting the specialized metadata will still be able to open a GeoTIFF format file.
Keyhole Markup Language (KML) is an XML notation for expressing geographic annotation and visualization within two-dimensional maps and three-dimensional Earth browsers. KML was developed for use with Google Earth, which was originally named Keyhole Earth Viewer. It was created by Keyhole, Inc, which was acquired by Google in 2004. KML became an international standard of the Open Geospatial Consortium in 2008. Google Earth was the first program able to view and graphically edit KML files, but other projects such as Marble have added KML support.
A spatial reference system (SRS) or coordinate reference system (CRS) is a framework used to precisely measure locations on the surface of the Earth as coordinates. It is thus the application of the abstract mathematics of coordinate systems and analytic geometry to geographic space. A particular SRS specification comprises a choice of Earth ellipsoid, horizontal datum, map projection, origin point, and unit of measure. Thousands of coordinate systems have been specified for use around the world or in specific regions and for various purposes, necessitating transformations between different SRS.
Simple Features is a set of standards that specify a common storage and access model of geographic feature made of mostly two-dimensional geometries used by geographic information systems. It is formalized by both the Open Geospatial Consortium (OGC) and the International Organization for Standardization (ISO).
A spatial database is a general-purpose database that has been enhanced to include spatial data that represents objects defined in a geometric space, along with tools for querying and analyzing such data. Most spatial databases allow the representation of simple geometric objects such as points, lines and polygons. Some spatial databases handle more complex structures such as 3D objects, topological coverages, linear networks, and triangulated irregular networks (TINs). While typical databases have developed to manage various numeric and character types of data, such databases require additional functionality to process spatial data types efficiently, and developers have often added geometry or feature data types. The Open Geospatial Consortium (OGC) developed the Simple Features specification and sets standards for adding spatial functionality to database systems. The SQL/MM Spatial ISO/IEC standard is a part the SQL/MM multimedia standard and extends the Simple Features standard with data types that support circular interpolations. Almost all current relational and object-relational database management systems now have spatial extensions, and some GIS software vendors have developed their own spatial extensions to database management systems.
Geospatial metadata is a type of metadata applicable to geographic data and information. Such objects may be stored in a geographic information system (GIS) or may simply be documents, data-sets, images or other objects, services, or related items that exist in some other native environment but whose features may be appropriate to describe in a (geographic) metadata catalog.
A Spatial Data Infrastructure (SDI), also called geospatial data infrastructure, is a data infrastructure implementing a framework of geographic data, metadata, users and tools that are interactively connected in order to use spatial data in an efficient and flexible way. Another definition is "the technology, policies, standards, human resources, and related activities necessary to acquire, process, distribute, use, maintain, and preserve spatial data".
The Open Geospatial Consortium Web Coverage Service Interface Standard (WCS) defines Web-based retrieval of coverages – that is, digital geospatial information representing space/time-varying phenomena.
Observations and Measurements (O&M) is an international standard which defines a conceptual schema encoding for observations, and for features involved in sampling when making observations. While the O&M standard was developed in the context of geographic information systems, the model is derived from generic patterns proposed by Fowler and Odell, and is not limited to geospatial information. O&M is one of the core standards in the OGC Sensor Web Enablement suite, providing the response model for Sensor Observation Service (SOS).
The Open Geospatial Consortium (OGC), an international voluntary consensus standards organization for geospatial content and location-based services, sensor web and Internet of Things, GIS data processing and data sharing. It originated in 1994 and involves more than 500 commercial, governmental, nonprofit and research organizations in a consensus process encouraging development and implementation of open standards.
WaterML is a technical standard and information model used to represent hydrological time series structures. The current version is WaterML 2.0, released an open standard of the Open Geospatial Consortium (OGC).
The Web Coverage Processing Service (WCPS) defines a language for filtering and processing of multi-dimensional raster coverages, such as sensor, simulation, image, and statistics data. The Web Coverage Processing Service is maintained by the Open Geospatial Consortium (OGC). This raster query language allows clients to obtain original coverage data, or derived information, in a platform-neutral manner over the Web.
GeoSPARQL is a standard for representation and querying of geospatial linked data for the Semantic Web from the Open Geospatial Consortium (OGC). The definition of a small ontology based on well-understood OGC standards is intended to provide a standardized exchange basis for geospatial RDF data which can support both qualitative and quantitative spatial reasoning and querying with the SPARQL database query language.
The Augmented Reality Markup Language (ARML) is a data standard to describe and interact with augmented reality (AR) scenes. It has been developed within the Open Geospatial Consortium (OGC) by a dedicated ARML 2.0 Standards Working Group. ARML consists of both an XML grammar to describe the location and appearance of virtual objects in the scene, as well as ECMAScript bindings to allow dynamic access to the properties of the virtual objects, as well as event handling, and is currently published in version 2.0. ARML focuses on visual augmented reality.
A GeoPackage (GPKG) is an open, non-proprietary, platform-independent and standards-based data format for geographic information system implemented as a SQLite database container. Defined by the Open Geospatial Consortium (OGC) with the backing of the US military and published in 2014, GeoPackage has seen widespread support from various government, commercial, and open source organizations.