Changes between Version 2 and Version 3 of GEOSGeometry
 Timestamp:
 08/15/2007 08:41:56 PM (8 years ago)
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GEOSGeometry
v2 v3 17 17 18 18 ''Features'': 19 * A BSD 20 * Looselycoupled to !GeoDjango, ''e.g.'', GEOS geometry objects may be used outside a django project/application (no need have {{{DJANGO_SETTINGS_MODULE}}} set).19 * A BSDlicensed interface to the GEOS geometry routines, implemented purely in Python using {{{ctypes}}}. 20 * Looselycoupled to !GeoDjango, ''e.g.'', GEOS geometry objects may be used outside a django project/application (no need to have {{{DJANGO_SETTINGS_MODULE}}} set). 21 21 * Mutability. GEOS Geometry objects may be modified, and memory is safely reused when possible. 22 22 * Crossplatform and tested. !GeoDjango GEOS geometries are welltested and compatible with Windows, Linux, Solaris, and Mac OSX platforms. 23 23 24 24 === Related Work === 25 Upon learning of the GEOS Geometry work in GeoDjango in May, 2007, Sean Gillies began implementation of PCL's {{{ctypes}}} interface to GEOS, called [http://trac.gispython.org/projects/PCL/wiki/ShapeLy ShapeLy]. !ShapeLy is still evolving, ''e.g.'', it lacks support for the full GEOS API, mutable geometries, and fullyfunctional constructors for Polygons and !GeometryCollections. However, the PCL team is implementing exciting features including a geometry interface (similar to NumPy's [http://numpy.scipy.org/array_interface.shtml array interface]) and excellent GeoJSON support. 26 27 Because !ShapeLy is licensed under the LGPL, I (Justin Bronn) declined to merge the projects. ''See'' [http://lists.gispython.org/pipermail/community/2007May/000964.html Proposal to launch the Shapely project], GISPython.com mailing list. 25 28 26 29 == Geometry Objects == 27 30 31 '''Note:''' The images shown below are courtesy of the [http://www.jumpproject.org/project.php?PID=JTS&SID=OVER Java Topology Suite (JTS) webpage], Copyright (C) 2003, [http://www.jumpproject.org/ The JUMPProject . Org]. 32 28 33 === Point === 29 34 30 The Point object may be initialized with either a tuple, or individual parameters. For example: 35 {{{ 36 #!html 37 <img src="http://www.jumpproject.org/inc/JTS/img/GeometryPoint.gif"> 38 }}} 39 40 The {{{Point}}} object may be initialized with either a tuple, or individual parameters. For example: 31 41 {{{ 32 42 #!python … … 38 48 === !LineString === 39 49 40 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: 50 {{{ 51 #!html 52 <img src="http://www.jumpproject.org/inc/JTS/img/GeometryLineString.gif"> 53 }}} 54 55 {{{LineString}}} objects initialize on a given sequence. For example, the constructor may take lists, tuples, [http://numpy.scipy.org/ 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: 41 56 42 57 {{{ … … 51 66 52 67 === !LinearRing === 68 {{{ 69 #!html 70 <img src="http://www.jumpproject.org/inc/JTS/img/GeometryLinearRing.gif"> 71 }}} 72 73 {{{LinearRing}}} objects are subclasses of {{{LineString}}} objects, however, an error will be thrown if the points used during initialization do not form a closed linestring. 74 75 {{{ 76 #!python 77 >>> from django.contrib.gis.geos import LinearRing 78 >>> lr = LinearRing((0, 0), (0, 1), (1, 1), (1, 0), (0, 0)) 79 >>> lr = LinearRing((0, 0), (0, 1)) 80 GEOS_ERROR: IllegalArgumentException: points must form a closed linestring 81 ... 82 }}} 53 83 54 84 === Polygon === 85 86 {{{ 87 #!html 88 <img src="http://www.jumpproject.org/inc/JTS/img/GeometryPolygon.bmp"> 89 }}} 55 90 56 91 == Geometry Collections == … … 77 112 78 113 === Output Properties === 79 * {{{wkt}}}: Returns the WellKnown Text of the geometry (an OGC standard). 80 * {{{hex}}}: Returns the HEXEWKB PostGIS canonical representation of the geometry. This representation is specific to PostGIS, and is not a standard. 81 * {{{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. 114 * {{{wkt}}} 115 * Returns the WellKnown Text of the geometry (an OGC standard). 116 * {{{hex}}} 117 * Returns the HEXEWKB PostGIS canonical representation of the geometry. This representation is specific to PostGIS, and is not a standard. 118 * {{{kml}}} 119 * Returns a [http://code.google.com/apis/kml/documentation/ 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. 82 120 83 121 === Spatial Predicate Properties === 84 * empty 85 * valid 86 * simple 87 * ring 88 * hasz 122 * {{{empty}}} 123 * Returns whether or not the set of points in the geometry is empty. 124 * {{{valid}}} 125 * Returns a boolean indicating whether the geometry is valid. 126 * {{{simple}}} 127 * A Geometry is simple if and only if the only selfintersections are at boundary points. For example, a {{{LineString}}} object is not simple if it intersects itself (like the one pictured above). Thus, {{{LinearRing}}} and {{{Polygon}}} objects are always simple because they do not intersect themselves. 128 * {{{ring}}} 129 * Returns a boolean indicating whether the geometry is a {{{LinearRing}}}. 130 * {{{hasz}}} 131 * Returns a boolean indicating whether the geometry is threedimensional. 89 132 90 133 === Spatial Predicate Methods === 91 * contains() 92 * crosses() 93 * disjoint() 94 * equals() 95 * equals_exact() 96 * intersects() 97 * overlaps() 98 * relate_pattern() 99 * within() 134 All of the following spatial predicate methods take another GEOS Geometry instance as an argument (referred to below as {{{other}}}). 135 * {{{contains(other)}}} 136 * {{{crosses(other)}}} 137 * {{{disjoint(other)}}} 138 * {{{equals(other)}}} 139 * {{{equals_exact(other)}}} 140 * {{{intersects(other)}}} 141 * {{{overlaps(other)}}} 142 * {{{relate_pattern(other)}}} 143 * {{{within(other)}}} 100 144 101 145 === Topological Methods === 102 * buffer()103 * difference()104 * intersection()105 * relate()106 * sym_difference()107 * union()146 * {{{buffer()}}} 147 * {{{difference()}}} 148 * {{{intersection()}}} 149 * {{{relate()}}} 150 * {{{sym_difference()}}} 151 * {{{union()}}} 108 152 109 153 === Topological Properties === 110 * area111 * boundary112 * centroid113 * convex_hull114 * envelope115 * point_on_surface154 * {{{area}}} 155 * {{{boundary}}} 156 * {{{centroid}}} 157 * {{{convex_hull}}} 158 * {{{envelope}}} 159 * {{{point_on_surface}}}