[[TOC()]] = GEOS Geometries = == Background == === What is GEOS? === [http://geos.refractions.net/ GEOS] stands for '''G'''eometry '''E'''ngine - '''O'''pen '''S'''ource, and is a C++ port of the [http://www.jump-project.org/project.php?PID=JTS&SID=OVER Java Topology Suite], implementing the OpenGIS [http://www.opengeospatial.org/standards/sfs Simple Features for SQL] spatial predicate functions and spatial operators. GEOS is developed and maintained by [http://www.refractions.net/ Refractions Research] of Victoria, Canada. === Why the new API? === 1. The GEOS SWIG wrapper is no longer maintained, and requires the installation of SWIG. * ''See'' Sean Gillies, ''[http://zcologia.com/news/150/geometries-for-python/ Geometries for Python]'' (blog post explaining rationale for abandoning GEOS support); ''see also'' Sean's message on the [http://geos.refractions.net/pipermail/geos-devel/2007-March/002851.html GEOS-Devel Mailing List] (Mar. 5, 2007). 2. The [http://trac.gispython.org/projects/PCL/browser/PCL/trunk/PCL-Core/cartography/geometry PCL implementation] is over 2K+ lines of C and would make PCL a requisite package for the GeoDjango application stack. 3. Cross-platform compatibility. Thus, the Python {{{ctypes}}} package was used to wrap the [http://geos.refractions.net/ro/doxygen_docs/html/geos__c_8h-source.html GEOS C API] to bring the rich capabilities of GEOS to Python and !GeoDjango. ''Features'': * A BSD licensed interface to the GEOS geometry routines, implemented purely in Python using {{{ctypes}}}. * Loosely-coupled to !GeoDjango, ''e.g.'', GEOS geometry objects may be used outside a django project/application (no need have {{{DJANGO_SETTINGS_MODULE}}} set). * Mutability. GEOS Geometry objects may be modified, and memory is safely re-used when possible. * Cross-platform and tested. !GeoDjango GEOS geometries are well-tested and compatible with Windows, Linux, Solaris, and Mac OSX platforms. === Related Work === == Geometry Objects == === Point === The Point object may be initialized with either a tuple, or individual parameters. For example: {{{ #!python >>> from django.contrib.gis.geos import Point >>> p = Point((5, 23)) # 2D point, passed in as a tuple >>> p = Point(5, 23, 8) # 3D point, passed in with individual parameters }}} === !LineString === Initializes on the given sequence, for example, the constructor may take lists, tuples, !NumPy arrays of X,Y[,Z] pairs, or {{{Point}}} objects. If {{{Point}}} objects are used, ownership of the points is ''not'' transferred to the {{{LineString}}} object. Examples: {{{ #!python >>> from django.contrib.gis.geos import LineString, Point >>> ls = LineString((1, 1), (2, 2)) >>> ls = LineString([(1, 1), (2, 2)]) >>> ls = LineString(Point(1, 1), Point(2, 2)) >>> from numpy import array >>> ls = LineString(array([(1, 1), (2, 2)])) }}} === !LinearRing === === Polygon === == Geometry Collections == === !MultiPoint === === !MultiLineString === === !MultiPolygon === === !GeometryCollection === == API == === Creation === GEOS geometry objects may be created from strings using the {{{fromstr()}}} factory, or using the constructor for each geometry object (as described above). {{{ #!python >>> from django.contrib.gis.geos import fromstr >>> pnt = fromstr('POINT(-90.5 29.5)', srid=4326) }}} The {{{srid}}} keyword may be used to set the spatial reference system identifier number for the geometry. This will be used to conduct any needed transformations for spatial lookups and geographic model creation. It should be noted that {{{fromstr}}} is a shortcut to the constructor for the base {{{GEOSGeometry}}} object. === Output Properties === * {{{wkt}}}: Returns the Well-Known Text of the geometry (an OGC standard). * {{{hex}}}: Returns the HEXEWKB PostGIS canonical representation of the geometry. This representation is specific to PostGIS, and is not a standard. * {{{kml}}}: Returns a KML (Keyhole Markup Language) representation of the geometry. Should only be used for geometries with an SRID of 4326 (WGS84), but this restriction is not enforced. === Spatial Predicate Properties === * empty * valid * simple * ring * hasz === Spatial Predicate Methods === * contains() * crosses() * disjoint() * equals() * equals_exact() * intersects() * overlaps() * relate_pattern() * within() === Topological Methods === * buffer() * difference() * intersection() * relate() * sym_difference() * union() === Topological Properties === * area * boundary * centroid * convex_hull * envelope * point_on_surface