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OpenGIS Abstract Specifications
Start with Topic 0 Overview -Introduction and roadmap to the Abstract specification.
It describes the common architecture for simple feature geometry. The base Geometry class has subclasses for Point, Curve, Surface and GeometryCollection. Each geometric object is associated with a Spatial Reference System, which describes the coordinate space in which the geometric object is defined. The extended Geometry model has specialized 0, 1 and 2-dimensional collection classes named MultiPoint, MultiLineString and MultiPolygon for modeling geometries corresponding to collections of Points, LineStrings and Polygons, respectively. MultiCurve and MultiSurface are introduced as abstract superclasses that generalize the collection interfaces to handle Curves and Surfaces.
4. Geography Markup Language - GML
GML
Any communication process involves the presence of a sender, a recipient and a communication channel. To understand the message transmitted by a sender (through an individual or a computer system) the receiver needs to know the encoding mechanism, i.e. the language used. Thus, in order to communicate, a common language is required. In digital geographic domain, the common language for communication is Geographic Markup Language.
Geography Markup Language (GML) is an open standard encoding geographic features and their (spatial and non-spatial) properties using the XML (eXtensible Markup Language) framework. GML is being specified by the OGC and was adopted as ISO Standards (ISO 19136:2007 ) in 20017. It is the basis of communication within geospatial community, by enabling a vendor-neutral exchange of spatial data. Each storage data format (e.g. shapefile, Oracle, PostGIS) can be converted to GML and then published online via web services. Uses of GML: interoperable exchange of geographic data; common format for transferring data between different GIS, Data storage.
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