![]() Currently local, geographic and projected coordinate systems are supported. The OGRSpatialReference class is intended to store an OpenGIS Spatial Reference System definition. On the other side, when retrieving data from the OGR C API, the OGRSetNonLinearGeometriesEnabledFlag() function can be used, so that geometries and layer geometry type returned are also converted to their linear approximation if necessary. Generic mechanisms have been introduced so that creating or modifying a feature with a non-linear geometry in a layer of a driver that does not support it will transform that geometry in the closest matching linear geometry. Compatibility issues with non-linear geometries In particular, it would be possible to create specialized classes using the OGRGeometryFactory without modifying it. While it is theoretically possible to derive other or more specific geometry classes from the existing OGRGeometry classes, this isn't an aspect that has been well thought out. Many of the spatial analysis methods (such as computing overlaps and so forth) are not implemented at this time for OGRGeometry. This is normally a reference to a shared spatial reference object with reference counting for each of the OGRGeometry objects using it. In a manner based on the geometry object in SFCOM, the OGRGeometry includes a reference to an OGRSpatialReference object, defining the spatial reference system of that geometry. These are predefined ASCII and binary formats for representing all the types of simple features geometries. The OGRGeometryFactory is used to convert well known text, and well known binary format data into geometries. In most cases the methods are aggregated into other classes. Some intermediate interfaces modeled in the simple features abstract model and SFCOM are not modeled in OGR at this time. These include OGRCurve (base class for OGRLineString) and OGRSurface (base class for OGRPolygon). Those geometry type are extended with non-linear geometries with the OGRCircularString, OGRCompoundCurve, OGRCurvePolygon, OGRMultiCurve and OGRMultiSurface classes.Īdditional intermediate abstract base classes contain functionality that could eventually be implemented by other geometry types. Types of geometry include OGRPoint, OGRLineString, OGRPolygon, OGRGeometr圜ollection, OGRMultiPolygon, OGRMultiPoint, and OGRMultiLineString. All the geometry classes derived from OGRGeometry which defines the common services of all geometries. The geometry classes are represent various kinds of vector geometry. All available drivers are managed by the GDALDriverManager. Layer ( ogrsf_frmts.h): OGRLayer is an abstract base class represent a layer of features in an GDALDataset.ĭataset ( gdal_priv.h): A GDALDataset is an abstract base class representing a file or database containing one or more OGRLayer objects.ĭrivers (gdal_priv.h): A GDALDriver represents a translator for a specific format, opening GDALDataset objects. Spatial Reference ( ogr_spatialref.h): An OGRSpatialReference encapsulates the definition of a projection and datum.įeature ( ogr_feature.h): The OGRFeature encapsulates the definition of a whole feature, that is a geometry and a set of attributes.įeature Class Definition ( ogr_feature.h): The OGRFeatureDefn class captures the schema (set of field definitions) for a group of related features (normally a whole layer). A geometry includes a spatial reference system (projection). Geometry ( ogr_geometry.h): The geometry classes ( OGRGeometry, etc) encapsulate the OpenGIS model vector data as well as providing some geometry operations, and translation to/from well known binary and text format. Data types, and method names are modeled on those from the interface specifications. ![]() It is intended that these same OGR classes could be used by an implementation of SFCORBA for instance or used directly by C++ programs wanting to use an OpenGIS simple features inspired API.īecause OGR is modeled on the OpenGIS simple features data model, it is very helpful to review the SFCOM, or other simple features interface specifications which can be retrieved from the Open Geospatial Consortium web site. The OGR classes are intended to be generic (not specific to OLE DB or COM or Windows) but are used as a foundation for implementing OLE DB Provider support, as well as client side support for SFCOM. This document is intended to document the OGR classes.
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