GEOS stands for Geometry Engine - Open Source, and is a C++ library, ported from the Java Topology Suite. GEOS implements the OpenGIS Simple Features for SQL spatial predicate functions and spatial operators. GEOS, now an OSGeo project, was initially developed and maintained by Refractions Research of Victoria, Canada.
GeoDjango implements a high-level Python wrapper for the GEOS library, its features include:
ctypes.GEOSGeometry objects
may be used outside of a Django project/application. In other words,
no need to have DJANGO_SETTINGS_MODULE set or use a database, etc.GEOSGeometry objects may be modified.This section contains a brief introduction and tutorial to using
GEOSGeometry objects.
GEOSGeometry objects may be created in a few ways. The first is
to simply instantiate the object on some spatial input – the following
are examples of creating the same geometry from WKT, HEX, WKB, and GeoJSON:
>>> from django.contrib.gis.geos import GEOSGeometry
>>> pnt = GEOSGeometry('POINT(5 23)') # WKT
>>> pnt = GEOSGeometry('010100000000000000000014400000000000003740') # HEX
>>> pnt = GEOSGeometry(buffer('\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x14@\x00\x00\x00\x00\x00\x007@'))
>>> pnt = GEOSGeometry('{ "type": "Point", "coordinates": [ 5.000000, 23.000000 ] }') # GeoJSON
Another option is to use the constructor for the specific geometry type
that you wish to create. For example, a Point object may be
created by passing in the X and Y coordinates into its constructor:
>>> from django.contrib.gis.geos import Point
>>> pnt = Point(5, 23)
All these constructors take the keyword argument srid. For example:
>>> from django.contrib.gis.geos import GEOSGeometry, LineString, Point
>>> print(GEOSGeometry('POINT (0 0)', srid=4326))
SRID=4326;POINT (0 0)
>>> print(LineString((0, 0), (1, 1), srid=4326))
SRID=4326;LINESTRING (0 0, 1 1)
>>> print(Point(0, 0, srid=32140))
SRID=32140;POINT (0 0)
Finally, there is the fromfile() factory method which returns a
GEOSGeometry object from a file:
>>> from django.contrib.gis.geos import fromfile
>>> pnt = fromfile('/path/to/pnt.wkt')
>>> pnt = fromfile(open('/path/to/pnt.wkt'))
GEOSGeometry objects are ‘Pythonic’, in other words components may
be accessed, modified, and iterated over using standard Python conventions.
For example, you can iterate over the coordinates in a Point:
>>> pnt = Point(5, 23)
>>> [coord for coord in pnt]
[5.0, 23.0]
With any geometry object, the GEOSGeometry.coords property
may be used to get the geometry coordinates as a Python tuple:
>>> pnt.coords
(5.0, 23.0)
You can get/set geometry components using standard Python indexing
techniques. However, what is returned depends on the geometry type
of the object. For example, indexing on a LineString
returns a coordinate tuple:
>>> from django.contrib.gis.geos import LineString
>>> line = LineString((0, 0), (0, 50), (50, 50), (50, 0), (0, 0))
>>> line[0]
(0.0, 0.0)
>>> line[-2]
(50.0, 0.0)
Whereas indexing on a Polygon will return the ring
(a LinearRing object) corresponding to the index:
>>> from django.contrib.gis.geos import Polygon
>>> poly = Polygon( ((0.0, 0.0), (0.0, 50.0), (50.0, 50.0), (50.0, 0.0), (0.0, 0.0)) )
>>> poly[0]
<LinearRing object at 0x1044395b0>
>>> poly[0][-2] # second-to-last coordinate of external ring
(50.0, 0.0)
In addition, coordinates/components of the geometry may added or modified, just like a Python list:
>>> line[0] = (1.0, 1.0)
>>> line.pop()
(0.0, 0.0)
>>> line.append((1.0, 1.0))
>>> line.coords
((1.0, 1.0), (0.0, 50.0), (50.0, 50.0), (50.0, 0.0), (1.0, 1.0))
Geometries support set-like operators:
>>> from django.contrib.gis.geos import LineString
>>> ls1 = LineString((0, 0), (2, 2))
>>> ls2 = LineString((1, 1), (3, 3))
>>> print(ls1 | ls2) # equivalent to `ls1.union(ls2)`
MULTILINESTRING ((0 0, 1 1), (1 1, 2 2), (2 2, 3 3))
>>> print(ls1 & ls2) # equivalent to `ls1.intersection(ls2)`
LINESTRING (1 1, 2 2)
>>> print(ls1 - ls2) # equivalent to `ls1.difference(ls2)`
LINESTRING(0 0, 1 1)
>>> print(ls1 ^ ls2) # equivalent to `ls1.sym_difference(ls2)`
MULTILINESTRING ((0 0, 1 1), (2 2, 3 3))
Equality operator doesn’t check spatial equality
The GEOSGeometry equality operator uses
equals_exact(), not equals(), i.e.
it requires the compared geometries to have the same coordinates in the
same positions with the same SRIDs:
>>> from django.contrib.gis.geos import LineString
>>> ls1 = LineString((0, 0), (1, 1))
>>> ls2 = LineString((1, 1), (0, 0))
>>> ls3 = LineString((1, 1), (0, 0), srid=4326)
>>> ls1.equals(ls2)
True
>>> ls1 == ls2
False
>>> ls3 == ls2 # different SRIDs
False
Older versions didn’t check the srid when comparing
GEOSGeometry objects using the equality operator.
GEOSGeometry¶GEOSGeometry(geo_input, srid=None)¶| Parameters: |
|
|---|
This is the base class for all GEOS geometry objects. It initializes on the
given geo_input argument, and then assumes the proper geometry subclass
(e.g., GEOSGeometry('POINT(1 1)') will create a Point object).
The following input formats, along with their corresponding Python types, are accepted:
| Format | Input Type |
|---|---|
| WKT / EWKT | str or unicode |
| HEX / HEXEWKB | str or unicode |
| WKB / EWKB | buffer |
| GeoJSON | str or unicode |
GEOSGeometry.from_gml(gml_string)¶Constructs a GEOSGeometry from the given GML string.
GEOSGeometry.coords¶Returns the coordinates of the geometry as a tuple.
GEOSGeometry.dims¶Returns the dimension of the geometry:
0 for Points and MultiPoints1 for LineStrings and MultiLineStrings2 for Polygons and MultiPolygons-1 for empty GeometryCollectionsGeometryCollectionsGEOSGeometry.empty¶Returns whether or not the set of points in the geometry is empty.
GEOSGeometry.geom_type¶Returns a string corresponding to the type of geometry. For example:
>>> pnt = GEOSGeometry('POINT(5 23)')
>>> pnt.geom_type
'Point'
GEOSGeometry.geom_typeid¶Returns the GEOS geometry type identification number. The following table shows the value for each geometry type:
| Geometry | ID |
|---|---|
Point |
0 |
LineString |
1 |
LinearRing |
2 |
Polygon |
3 |
MultiPoint |
4 |
MultiLineString |
5 |
MultiPolygon |
6 |
GeometryCollection |
7 |
GEOSGeometry.num_coords¶Returns the number of coordinates in the geometry.
GEOSGeometry.num_geom¶Returns the number of geometries in this geometry. In other words, will return 1 on anything but geometry collections.
GEOSGeometry.hasz¶Returns a boolean indicating whether the geometry is three-dimensional.
GEOSGeometry.ring¶Returns a boolean indicating whether the geometry is a LinearRing.
GEOSGeometry.simple¶Returns a boolean indicating whether the geometry is ‘simple’. A geometry
is simple if and only if it does not intersect itself (except at boundary
points). For example, a LineString object is not simple if it
intersects itself. Thus, LinearRing and Polygon objects
are always simple because they do cannot intersect themselves, by
definition.
GEOSGeometry.valid¶Returns a boolean indicating whether the geometry is valid.
GEOSGeometry.valid_reason¶Returns a string describing the reason why a geometry is invalid.
GEOSGeometry.srid¶Property that may be used to retrieve or set the SRID associated with the geometry. For example:
>>> pnt = Point(5, 23)
>>> print(pnt.srid)
None
>>> pnt.srid = 4326
>>> pnt.srid
4326
The properties in this section export the GEOSGeometry object into
a different. This output may be in the form of a string, buffer, or even
another object.
GEOSGeometry.ewkt¶Returns the “extended” Well-Known Text of the geometry. This representation
is specific to PostGIS and is a superset of the OGC WKT standard. [1]
Essentially the SRID is prepended to the WKT representation, for example
SRID=4326;POINT(5 23).
Note
The output from this property does not include the 3dm, 3dz, and 4d information that PostGIS supports in its EWKT representations.
GEOSGeometry.hex¶Returns the WKB of this Geometry in hexadecimal form. Please note
that the SRID value is not included in this representation
because it is not a part of the OGC specification (use the
GEOSGeometry.hexewkb property instead).
GEOSGeometry.hexewkb¶Returns the EWKB of this Geometry in hexadecimal form. This is an extension of the WKB specification that includes the SRID value that are a part of this geometry.
GEOSGeometry.json¶Returns the GeoJSON representation of the geometry. Note that the result is
not a complete GeoJSON structure but only the geometry key content of a
GeoJSON structure. See also GeoJSON Serializer.
GEOSGeometry.geojson¶Alias for GEOSGeometry.json.
GEOSGeometry.kml¶Returns a KML (Keyhole Markup Language) representation of the geometry. This should only be used for geometries with an SRID of 4326 (WGS84), but this restriction is not enforced.
GEOSGeometry.ogr¶Returns an OGRGeometry object
corresponding to the GEOS geometry.
GEOSGeometry.wkb¶Returns the WKB (Well-Known Binary) representation of this Geometry
as a Python buffer. SRID value is not included, use the
GEOSGeometry.ewkb property instead.
GEOSGeometry.ewkb¶Return the EWKB representation of this Geometry as a Python buffer. This is an extension of the WKB specification that includes any SRID value that are a part of this geometry.
GEOSGeometry.wkt¶Returns the Well-Known Text of the geometry (an OGC standard).
Non-significant zeros are stripped from the output.
All of the following spatial predicate methods take another
GEOSGeometry instance (other) as a parameter, and
return a boolean.
GEOSGeometry.contains(other)¶Returns True if other.within(this) returns
True.
GEOSGeometry.covers(other)¶Returns True if this geometry covers the specified geometry.
The covers predicate has the following equivalent definitions:
T*****FF*, *T****FF*, ***T**FF*, or ****T*FF*.If either geometry is empty, returns False.
This predicate is similar to GEOSGeometry.contains(), but is more
inclusive (i.e. returns True for more cases). In particular, unlike
contains() it does not distinguish between points in the
boundary and in the interior of geometries. For most situations,
covers() should be preferred to contains(). As an
added benefit, covers() is more amenable to optimization and hence
should outperform contains().
GEOSGeometry.crosses(other)¶Returns True if the DE-9IM intersection matrix for the two Geometries
is T*T****** (for a point and a curve,a point and an area or a line
and an area) 0******** (for two curves).
GEOSGeometry.disjoint(other)¶Returns True if the DE-9IM intersection matrix for the two geometries
is FF*FF****.
GEOSGeometry.equals(other)¶Returns True if the DE-9IM intersection matrix for the two geometries
is T*F**FFF*.
GEOSGeometry.equals_exact(other, tolerance=0)¶Returns true if the two geometries are exactly equal, up to a
specified tolerance. The tolerance value should be a floating
point number representing the error tolerance in the comparison, e.g.,
poly1.equals_exact(poly2, 0.001) will compare equality to within
one thousandth of a unit.
GEOSGeometry.intersects(other)¶Returns True if GEOSGeometry.disjoint() is False.
GEOSGeometry.overlaps(other)¶Returns true if the DE-9IM intersection matrix for the two geometries
is T*T***T** (for two points or two surfaces) 1*T***T**
(for two curves).
GEOSGeometry.relate_pattern(other, pattern)¶Returns True if the elements in the DE-9IM intersection matrix
for this geometry and the other matches the given pattern –
a string of nine characters from the alphabet: {T, F, *, 0}.
GEOSGeometry.touches(other)¶Returns True if the DE-9IM intersection matrix for the two geometries
is FT*******, F**T***** or F***T****.
GEOSGeometry.within(other)¶Returns True if the DE-9IM intersection matrix for the two geometries
is T*F**F***.
GEOSGeometry.buffer(width, quadsegs=8)¶Returns a GEOSGeometry that represents all points whose distance
from this geometry is less than or equal to the given width. The
optional quadsegs keyword sets the number of segments used to
approximate a quarter circle (defaults is 8).
GEOSGeometry.difference(other)¶Returns a GEOSGeometry representing the points making up this
geometry that do not make up other.
GEOSGeometry.interpolate(distance)¶GEOSGeometry.interpolate_normalized(distance)¶Given a distance (float), returns the point (or closest point) within the
geometry (LineString or MultiLineString) at that distance.
The normalized version takes the distance as a float between 0 (origin) and
1 (endpoint).
Reverse of GEOSGeometry.project().
GEOSGeometry.intersection(other)¶Returns a GEOSGeometry representing the points shared by this
geometry and other.
GEOSGeometry.project(point)¶GEOSGeometry.project_normalized(point)¶Returns the distance (float) from the origin of the geometry
(LineString or MultiLineString) to the point projected on
the geometry (that is to a point of the line the closest to the given
point). The normalized version returns the distance as a float between 0
(origin) and 1 (endpoint).
Reverse of GEOSGeometry.interpolate().
GEOSGeometry.relate(other)¶Returns the DE-9IM intersection matrix (a string) representing the topological relationship between this geometry and the other.
GEOSGeometry.simplify(tolerance=0.0, preserve_topology=False)¶Returns a new GEOSGeometry, simplified to the specified tolerance
using the Douglas-Peucker algorithm. A higher tolerance value implies
fewer points in the output. If no tolerance is provided, it defaults to 0.
By default, this function does not preserve topology. For example,
Polygon objects can be split, be collapsed into lines, or
disappear. Polygon holes can be created or disappear, and lines may
cross. By specifying preserve_topology=True, the result will have the
same dimension and number of components as the input; this is significantly
slower, however.
GEOSGeometry.sym_difference(other)¶Returns a GEOSGeometry combining the points in this geometry
not in other, and the points in other not in this geometry.
GEOSGeometry.union(other)¶Returns a GEOSGeometry representing all the points in this
geometry and the other.
GEOSGeometry.boundary¶Returns the boundary as a newly allocated Geometry object.
GEOSGeometry.centroid¶Returns a Point object representing the geometric center of
the geometry. The point is not guaranteed to be on the interior
of the geometry.
GEOSGeometry.convex_hull¶Returns the smallest Polygon that contains all the points in
the geometry.
GEOSGeometry.envelope¶Returns a Polygon that represents the bounding envelope of
this geometry. Note that it can also return a Point if the input
geometry is a point.
GEOSGeometry.point_on_surface¶Computes and returns a Point guaranteed to be on the interior
of this geometry.
GEOSGeometry.unary_union¶Computes the union of all the elements of this geometry.
The result obeys the following contract:
LineStrings has the effect of fully noding and
dissolving the linework.Polygons will always return a Polygon
or MultiPolygon geometry (unlike GEOSGeometry.union(),
which may return geometries of lower dimension if a topology collapse
occurs).GEOSGeometry.area¶This property returns the area of the Geometry.
GEOSGeometry.extent¶This property returns the extent of this geometry as a 4-tuple,
consisting of (xmin, ymin, xmax, ymax).
GEOSGeometry.clone()¶This method returns a GEOSGeometry that is a clone of the original.
GEOSGeometry.distance(geom)¶Returns the distance between the closest points on this geometry and the
given geom (another GEOSGeometry object).
Note
GEOS distance calculations are linear – in other words, GEOS does not perform a spherical calculation even if the SRID specifies a geographic coordinate system.
GEOSGeometry.length¶Returns the length of this geometry (e.g., 0 for a Point,
the length of a LineString, or the circumference of
a Polygon).
GEOSGeometry.prepared¶Returns a GEOS PreparedGeometry for the contents of this geometry.
PreparedGeometry objects are optimized for the contains, intersects,
covers, crosses, disjoint, overlaps, touches and within operations. Refer to
the Prepared Geometries documentation for more information.
GEOSGeometry.srs¶Returns a SpatialReference object
corresponding to the SRID of the geometry or None.
GEOSGeometry.transform(ct, clone=False)¶Transforms the geometry according to the given coordinate transformation
parameter (ct), which may be an integer SRID, spatial reference WKT
string, a PROJ.4 string, a
SpatialReference object, or a
CoordTransform object. By default, the
geometry is transformed in-place and nothing is returned. However if the
clone keyword is set, then the geometry is not modified and a
transformed clone of the geometry is returned instead.
Note
Raises GEOSException if GDAL is not
available or if the geometry’s SRID is None or less than 0. It
doesn’t impose any constraints on the geometry’s SRID if called with a
CoordTransform object.
In previous versions, it required the geometry’s SRID to be a
positive integer even if it was called with a
CoordTransform object.
GEOSGeometry.normalize()¶Converts this geometry to canonical form:
>>> g = MultiPoint(Point(0, 0), Point(2, 2), Point(1, 1))
>>> print(g)
MULTIPOINT (0 0, 2 2, 1 1)
>>> g.normalize()
>>> print(g)
MULTIPOINT (2 2, 1 1, 0 0)
Point¶Point(x=None, y=None, z=None, srid=None)¶Point objects are instantiated using arguments that represent the
component coordinates of the point or with a single sequence coordinates.
For example, the following are equivalent:
>>> pnt = Point(5, 23)
>>> pnt = Point([5, 23])
Empty Point objects may be instantiated by passing no arguments or an
empty sequence. The following are equivalent:
>>> pnt = Point()
>>> pnt = Point([])
In previous versions, an empty Point couldn’t be instantiated.
LineString¶LineString(*args, **kwargs)¶LineString objects are instantiated using arguments that are either a
sequence of coordinates or Point objects. For example, the
following are equivalent:
>>> ls = LineString((0, 0), (1, 1))
>>> ls = LineString(Point(0, 0), Point(1, 1))
In addition, LineString objects may also be created by passing in a
single sequence of coordinate or Point objects:
>>> ls = LineString( ((0, 0), (1, 1)) )
>>> ls = LineString( [Point(0, 0), Point(1, 1)] )
Empty LineString objects may be instantiated by passing no arguments
or an empty sequence. The following are equivalent:
>>> ls = LineString()
>>> ls = LineString([])
In previous versions, an empty LineString couldn’t be instantiated.
closed¶Returns whether or not this LineString is closed.
LinearRing¶LinearRing(*args, **kwargs)¶LinearRing objects are constructed in the exact same way as
LineString objects, however the coordinates must be closed, in
other words, the first coordinates must be the same as the last
coordinates. For example:
>>> ls = LinearRing((0, 0), (0, 1), (1, 1), (0, 0))
Notice that (0, 0) is the first and last coordinate – if they were not
equal, an error would be raised.
Polygon¶Polygon(*args, **kwargs)¶Polygon objects may be instantiated by passing in parameters that
represent the rings of the polygon. The parameters must either be
LinearRing instances, or a sequence that may be used to construct a
LinearRing:
>>> ext_coords = ((0, 0), (0, 1), (1, 1), (1, 0), (0, 0))
>>> int_coords = ((0.4, 0.4), (0.4, 0.6), (0.6, 0.6), (0.6, 0.4), (0.4, 0.4))
>>> poly = Polygon(ext_coords, int_coords)
>>> poly = Polygon(LinearRing(ext_coords), LinearRing(int_coords))
In previous versions, an empty Polygon couldn’t be instantiated.
from_bbox(bbox)¶Returns a polygon object from the given bounding-box, a 4-tuple
comprising (xmin, ymin, xmax, ymax).
num_interior_rings¶Returns the number of interior rings in this geometry.
Comparing Polygons
Note that it is possible to compare Polygon objects directly with <
or >, but as the comparison is made through Polygon’s
LineString, it does not mean much (but is consistent and quick).
You can always force the comparison with the area
property:
>>> if poly_1.area > poly_2.area:
>>> pass
MultiPoint¶MultiPoint(*args, **kwargs)¶MultiPoint objects may be instantiated by passing in Point
objects as arguments, or a single sequence of Point objects:
>>> mp = MultiPoint(Point(0, 0), Point(1, 1))
>>> mp = MultiPoint( (Point(0, 0), Point(1, 1)) )
In previous versions, an empty MultiPoint couldn’t be instantiated.
MultiLineString¶MultiLineString(*args, **kwargs)¶MultiLineString objects may be instantiated by passing in
LineString objects as arguments, or a single sequence of
LineString objects:
>>> ls1 = LineString((0, 0), (1, 1))
>>> ls2 = LineString((2, 2), (3, 3))
>>> mls = MultiLineString(ls1, ls2)
>>> mls = MultiLineString([ls1, ls2])
In previous versions, an empty MultiLineString couldn’t be
instantiated.
merged¶Returns a LineString representing the line merge of
all the components in this MultiLineString.
closed¶Returns True if and only if all elements are closed. Requires GEOS 3.5.
MultiPolygon¶MultiPolygon(*args, **kwargs)¶MultiPolygon objects may be instantiated by passing Polygon
objects as arguments, or a single sequence of Polygon objects:
>>> p1 = Polygon( ((0, 0), (0, 1), (1, 1), (0, 0)) )
>>> p2 = Polygon( ((1, 1), (1, 2), (2, 2), (1, 1)) )
>>> mp = MultiPolygon(p1, p2)
>>> mp = MultiPolygon([p1, p2])
In previous versions, an empty MultiPolygon couldn’t be
instantiated.
cascaded_union¶Deprecated since version 1.10: Use the GEOSGeometry.unary_union property instead.
Returns a Polygon that is the union of all of the component
polygons in this collection. The algorithm employed is significantly
more efficient (faster) than trying to union the geometries together
individually. [2]
GeometryCollection¶GeometryCollection(*args, **kwargs)¶GeometryCollection objects may be instantiated by passing in other
GEOSGeometry as arguments, or a single sequence of
GEOSGeometry objects:
>>> poly = Polygon( ((0, 0), (0, 1), (1, 1), (0, 0)) )
>>> gc = GeometryCollection(Point(0, 0), MultiPoint(Point(0, 0), Point(1, 1)), poly)
>>> gc = GeometryCollection((Point(0, 0), MultiPoint(Point(0, 0), Point(1, 1)), poly))
In previous versions, an empty GeometryCollection couldn’t be
instantiated.
In order to obtain a prepared geometry, just access the
GEOSGeometry.prepared property. Once you have a
PreparedGeometry instance its spatial predicate methods, listed below,
may be used with other GEOSGeometry objects. An operation with a prepared
geometry can be orders of magnitude faster – the more complex the geometry
that is prepared, the larger the speedup in the operation. For more information,
please consult the GEOS wiki page on prepared geometries.
For example:
>>> from django.contrib.gis.geos import Point, Polygon
>>> poly = Polygon.from_bbox((0, 0, 5, 5))
>>> prep_poly = poly.prepared
>>> prep_poly.contains(Point(2.5, 2.5))
True
fromfile(file_h)¶| Parameters: | file_h (a Python file object or a string path to the file) – input file that contains spatial data |
|---|---|
| Return type: | a GEOSGeometry corresponding to the spatial data in the file |
Example:
>>> from django.contrib.gis.geos import fromfile
>>> g = fromfile('/home/bob/geom.wkt')
fromstr(string, srid=None)¶| Parameters: | |
|---|---|
| Return type: | a |
fromstr(string, srid) is equivalent to
GEOSGeometry(string, srid).
Example:
>>> from django.contrib.gis.geos import fromstr
>>> pnt = fromstr('POINT(-90.5 29.5)', srid=4326)
The reader I/O classes simply return a GEOSGeometry instance from the
WKB and/or WKT input given to their read(geom) method.
WKBReader¶Example:
>>> from django.contrib.gis.geos import WKBReader
>>> wkb_r = WKBReader()
>>> wkb_r.read('0101000000000000000000F03F000000000000F03F')
<Point object at 0x103a88910>
WKTReader¶Example:
>>> from django.contrib.gis.geos import WKTReader
>>> wkt_r = WKTReader()
>>> wkt_r.read('POINT(1 1)')
<Point object at 0x103a88b50>
All writer objects have a write(geom) method that returns either the
WKB or WKT of the given geometry. In addition, WKBWriter objects
also have properties that may be used to change the byte order, and or
include the SRID value (in other words, EWKB).
WKBWriter(dim=2)¶WKBWriter provides the most control over its output. By default it
returns OGC-compliant WKB when its write method is called. However,
it has properties that allow for the creation of EWKB, a superset of the
WKB standard that includes additional information. See the
WKBWriter.outdim documentation for more details about the dim
argument.
The ability to pass the dim argument to the constructor was added.
write(geom)¶Returns the WKB of the given geometry as a Python buffer object.
Example:
>>> from django.contrib.gis.geos import Point, WKBWriter
>>> pnt = Point(1, 1)
>>> wkb_w = WKBWriter()
>>> wkb_w.write(pnt)
<read-only buffer for 0x103a898f0, size -1, offset 0 at 0x103a89930>
write_hex(geom)¶Returns WKB of the geometry in hexadecimal. Example:
>>> from django.contrib.gis.geos import Point, WKBWriter
>>> pnt = Point(1, 1)
>>> wkb_w = WKBWriter()
>>> wkb_w.write_hex(pnt)
'0101000000000000000000F03F000000000000F03F'
byteorder¶This property may be set to change the byte-order of the geometry representation.
| Byteorder Value | Description |
|---|---|
| 0 | Big Endian (e.g., compatible with RISC systems) |
| 1 | Little Endian (e.g., compatible with x86 systems) |
Example:
>>> from django.contrib.gis.geos import Point, WKBWriter
>>> wkb_w = WKBWriter()
>>> pnt = Point(1, 1)
>>> wkb_w.write_hex(pnt)
'0101000000000000000000F03F000000000000F03F'
>>> wkb_w.byteorder = 0
'00000000013FF00000000000003FF0000000000000'
outdim¶This property may be set to change the output dimension of the geometry representation. In other words, if you have a 3D geometry then set to 3 so that the Z value is included in the WKB.
| Outdim Value | Description |
|---|---|
| 2 | The default, output 2D WKB. |
| 3 | Output 3D WKB. |
Example:
>>> from django.contrib.gis.geos import Point, WKBWriter
>>> wkb_w = WKBWriter()
>>> wkb_w.outdim
2
>>> pnt = Point(1, 1, 1)
>>> wkb_w.write_hex(pnt) # By default, no Z value included:
'0101000000000000000000F03F000000000000F03F'
>>> wkb_w.outdim = 3 # Tell writer to include Z values
>>> wkb_w.write_hex(pnt)
'0101000080000000000000F03F000000000000F03F000000000000F03F'
srid¶Set this property with a boolean to indicate whether the SRID of the geometry should be included with the WKB representation. Example:
>>> from django.contrib.gis.geos import Point, WKBWriter
>>> wkb_w = WKBWriter()
>>> pnt = Point(1, 1, srid=4326)
>>> wkb_w.write_hex(pnt) # By default, no SRID included:
'0101000000000000000000F03F000000000000F03F'
>>> wkb_w.srid = True # Tell writer to include SRID
>>> wkb_w.write_hex(pnt)
'0101000020E6100000000000000000F03F000000000000F03F'
WKTWriter(dim=2, trim=False, precision=None)¶This class allows outputting the WKT representation of a geometry. See the
WKBWriter.outdim, trim, and precision attributes for
details about the constructor arguments.
The ability to pass the dim, trim, and precision arguments
to the constructor was added.
write(geom)¶Returns the WKT of the given geometry. Example:
>>> from django.contrib.gis.geos import Point, WKTWriter
>>> pnt = Point(1, 1)
>>> wkt_w = WKTWriter()
>>> wkt_w.write(pnt)
'POINT (1.0000000000000000 1.0000000000000000)'
outdim¶See WKBWriter.outdim.
trim¶This property is used to enable or disable trimming of unnecessary decimals.
>>> from django.contrib.gis.geos import Point, WKTWriter
>>> pnt = Point(1, 1)
>>> wkt_w = WKTWriter()
>>> wkt_w.trim
False
>>> wkt_w.write(pnt)
'POINT (1.0000000000000000 1.0000000000000000)'
>>> wkt_w.trim = True
>>> wkt_w.write(pnt)
'POINT (1 1)'
precision¶This property controls the rounding precision of coordinates;
if set to None rounding is disabled.
>>> from django.contrib.gis.geos import Point, WKTWriter
>>> pnt = Point(1.44, 1.66)
>>> wkt_w = WKTWriter()
>>> print(wkt_w.precision)
None
>>> wkt_w.write(pnt)
'POINT (1.4399999999999999 1.6599999999999999)'
>>> wkt_w.precision = 0
>>> wkt_w.write(pnt)
'POINT (1 2)'
>>> wkt_w.precision = 1
>>> wkt_w.write(pnt)
'POINT (1.4 1.7)'
Footnotes
| [1] | See PostGIS EWKB, EWKT and Canonical Forms, PostGIS documentation at Ch. 4.1.2. |
| [2] | For more information, read Paul Ramsey’s blog post about (Much) Faster Unions in PostGIS 1.4 and Martin Davis’ blog post on Fast polygon merging in JTS using Cascaded Union. |
GEOS_LIBRARY_PATH¶A string specifying the location of the GEOS C library. Typically,
this setting is only used if the GEOS C library is in a non-standard
location (e.g., /home/bob/lib/libgeos_c.so).
Note
The setting must be the full path to the C shared library; in
other words you want to use libgeos_c.so, not libgeos.so.
Jun 22, 2017