GEOS API¶
Background¶
What is GEOS?¶
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.
Features¶
GeoDjango implements a highlevel Python wrapper for the GEOS library, its features include:
 A BSDlicensed interface to the GEOS geometry routines, implemented purely
in Python using
ctypes
.  Looselycoupled to GeoDjango. For example,
GEOSGeometry
objects may be used outside of a Django project/application. In other words, no need to haveDJANGO_SETTINGS_MODULE
set or use a database, etc.  Mutability:
GEOSGeometry
objects may be modified.  Crossplatform and tested; compatible with Windows, Linux, Solaris, and macOS platforms.
Tutorial¶
This section contains a brief introduction and tutorial to using
GEOSGeometry
objects.
Creating a Geometry¶
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'))
Geometries are Pythonic¶
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] # secondtolast 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 setlike 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
Geometry Objects¶
GEOSGeometry
¶

class
GEOSGeometry
(geo_input, srid=None)¶ 参数:  geo_input  Geometry input value (string or buffer)
 srid (int)  spatial reference identifier
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 srid
parameter, if given, is set as the SRID of the created geometry if
geo_input
doesn't have an SRID. If different SRIDs are provided through the
geo_input
and srid
parameters, ValueError
is raised:
>>> from django.contrib.gis.geos import GEOSGeometry
>>> GEOSGeometry('POINT EMPTY', srid=4326).ewkt
'SRID=4326;POINT EMPTY'
>>> GEOSGeometry('SRID=4326;POINT EMPTY', srid=4326).ewkt
'SRID=4326;POINT EMPTY'
>>> GEOSGeometry('SRID=1;POINT EMPTY', srid=4326)
Traceback (most recent call last):
...
ValueError: Input geometry already has SRID: 1.
The following input formats, along with their corresponding Python types, are accepted:
Format  Input Type 

WKT / EWKT  str 
HEX / HEXEWKB  str 
WKB / EWKB  buffer 
GeoJSON  str 
For the GeoJSON format, the SRID is set based on the crs
member. If crs
isn't provided, the SRID defaults to 4326.

classmethod
GEOSGeometry.
from_gml
(gml_string)¶ Constructs a
GEOSGeometry
from the given GML string.
Properties¶

GEOSGeometry.
coords
¶ Returns the coordinates of the geometry as a tuple.

GEOSGeometry.
dims
¶ Returns the dimension of the geometry:
0
forPoint
s andMultiPoint
s1
forLineString
s andMultiLineString
s2
forPolygon
s andMultiPolygon
s1
for emptyGeometryCollection
s the maximum dimension of its elements for nonempty
GeometryCollection
s

GEOSGeometry.
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 threedimensional.

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
andPolygon
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
Output Properties¶
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" WellKnown 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)
.备注
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 (WellKnown 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 WellKnown Text of the geometry (an OGC standard).
Spatial Predicate Methods¶
All of the following spatial predicate methods take another
GEOSGeometry
instance (other
) as a parameter, and
return a boolean.

GEOSGeometry.
contains
(other)¶ Returns
True
ifother.within(this)
returnsTrue
.

GEOSGeometry.
covers
(other)¶ Returns
True
if this geometry covers the specified geometry.The
covers
predicate has the following equivalent definitions: Every point of the other geometry is a point of this geometry.
 The DE9IM Intersection Matrix for the two geometries is
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. returnsTrue
for more cases). In particular, unlikecontains()
it does not distinguish between points in the boundary and in the interior of geometries. For most situations,covers()
should be preferred tocontains()
. As an added benefit,covers()
is more amenable to optimization and hence should outperformcontains()
.

GEOSGeometry.
crosses
(other)¶ Returns
True
if the DE9IM intersection matrix for the two Geometries isT*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 DE9IM intersection matrix for the two geometries isFF*FF****
.

GEOSGeometry.
equals
(other)¶ Returns
True
if the DE9IM intersection matrix for the two geometries isT*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
ifGEOSGeometry.disjoint()
isFalse
.

GEOSGeometry.
overlaps
(other)¶ Returns true if the DE9IM 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 DE9IM intersection matrix for this geometry and the other matches the givenpattern
 a string of nine characters from the alphabet: {T
,F
,*
,0
}.

GEOSGeometry.
touches
(other)¶ Returns
True
if the DE9IM intersection matrix for the two geometries isFT*******
,F**T*****
orF***T****
.

GEOSGeometry.
within
(other)¶ Returns
True
if the DE9IM intersection matrix for the two geometries isT*F**F***
.
Topological Methods¶

GEOSGeometry.
buffer
(width, quadsegs=8)¶ Returns a
GEOSGeometry
that represents all points whose distance from this geometry is less than or equal to the givenwidth
. The optionalquadsegs
keyword sets the number of segments used to approximate a quarter circle (defaults is 8).

GEOSGeometry.
buffer_with_style
(width, quadsegs=8, end_cap_style=1, join_style=1, mitre_limit=5.0)¶ Same as
buffer()
, but allows customizing the style of the buffer.end_cap_style
can be round (1
), flat (2
), or square (3
).join_style
can be round (1
), mitre (2
), or bevel (3
). Mitre ratio limit (
mitre_limit
) only affects mitered join style.

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
orMultiLineString
) 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
orMultiLineString
) 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 DE9IM 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 DouglasPeucker 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 specifyingpreserve_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.
Topological Properties¶

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 aPoint
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:
 Unioning a set of
LineString
s has the effect of fully noding and dissolving the linework.  Unioning a set of
Polygon
s will always return aPolygon
orMultiPolygon
geometry (unlikeGEOSGeometry.union()
, which may return geometries of lower dimension if a topology collapse occurs).
 Unioning a set of
Other Properties & Methods¶

GEOSGeometry.
area
¶ This property returns the area of the Geometry.

GEOSGeometry.
extent
¶ This property returns the extent of this geometry as a 4tuple, 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
(anotherGEOSGeometry
object).备注
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 aLineString
, or the circumference of aPolygon
).

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 orNone
.

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 string, aSpatialReference
object, or aCoordTransform
object. By default, the geometry is transformed inplace and nothing is returned. However if theclone
keyword is set, then the geometry is not modified and a transformed clone of the geometry is returned instead.备注
Raises
GEOSException
if GDAL is not available or if the geometry's SRID isNone
or less than 0. It doesn't impose any constraints on the geometry's SRID if called with aCoordTransform
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
¶

class
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([])
LineString
¶

class
LineString
(*args, **kwargs)¶ LineString
objects are instantiated using arguments that are either a sequence of coordinates orPoint
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 orPoint
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([])

closed
¶ Returns whether or not this
LineString
is closed.

LinearRing
¶

class
LinearRing
(*args, **kwargs)¶ LinearRing
objects are constructed in the exact same way asLineString
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.
is_counterclockwise
¶ Returns whether this
LinearRing
is counterclockwise.

Polygon
¶

class
Polygon
(*args, **kwargs)¶ Polygon
objects may be instantiated by passing in parameters that represent the rings of the polygon. The parameters must either beLinearRing
instances, or a sequence that may be used to construct aLinearRing
:>>> 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))

classmethod
from_bbox
(bbox)¶ Returns a polygon object from the given boundingbox, a 4tuple comprising
(xmin, ymin, xmax, ymax)
.

num_interior_rings
¶ Returns the number of interior rings in this geometry.

classmethod
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
Geometry Collections¶
MultiPoint
¶
MultiLineString
¶

class
MultiLineString
(*args, **kwargs)¶ MultiLineString
objects may be instantiated by passing inLineString
objects as arguments, or a single sequence ofLineString
objects:>>> ls1 = LineString((0, 0), (1, 1)) >>> ls2 = LineString((2, 2), (3, 3)) >>> mls = MultiLineString(ls1, ls2) >>> mls = MultiLineString([ls1, ls2])

merged
¶ Returns a
LineString
representing the line merge of all the components in thisMultiLineString
.

closed
¶ Returns
True
if and only if all elements are closed.

MultiPolygon
¶

class
MultiPolygon
(*args, **kwargs)¶ MultiPolygon
objects may be instantiated by passingPolygon
objects as arguments, or a single sequence ofPolygon
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])
GeometryCollection
¶

class
GeometryCollection
(*args, **kwargs)¶ GeometryCollection
objects may be instantiated by passing in otherGEOSGeometry
as arguments, or a single sequence ofGEOSGeometry
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))
Prepared Geometries¶
In order to obtain a prepared geometry, 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.
例子：
>>> 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
Geometry Factories¶

fromfile
(file_h)¶ 参数: file_h (a Python file
object or a string path to the file)  input file that contains spatial data返回类型: a GEOSGeometry
corresponding to the spatial data in the file举例：
>>> from django.contrib.gis.geos import fromfile >>> g = fromfile('/home/bob/geom.wkt')

fromstr
(string, srid=None)¶ 参数: 返回类型: a
GEOSGeometry
corresponding to the spatial data in the stringfromstr(string, srid)
is equivalent toGEOSGeometry(string, srid)
.举例：
>>> from django.contrib.gis.geos import fromstr >>> pnt = fromstr('POINT(90.5 29.5)', srid=4326)
I/O Objects¶
Reader Objects¶
The reader I/O classes return a GEOSGeometry
instance from the WKB
and/or WKT input given to their read(geom)
method.

class
WKBReader
¶ 举例：
>>> from django.contrib.gis.geos import WKBReader >>> wkb_r = WKBReader() >>> wkb_r.read('0101000000000000000000F03F000000000000F03F') <Point object at 0x103a88910>

class
WKTReader
¶ 举例：
>>> from django.contrib.gis.geos import WKTReader >>> wkt_r = WKTReader() >>> wkt_r.read('POINT(1 1)') <Point object at 0x103a88b50>
Writer Objects¶
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).

class
WKBWriter
(dim=2)¶ WKBWriter
provides the most control over its output. By default it returns OGCcompliant WKB when itswrite
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 theWKBWriter.outdim
documentation for more details about thedim
argument.
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) <readonly 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 byteorder of the geometry representation.
Byteorder Value 描述 0 Big Endian (e.g., compatible with RISC systems) 1 Little Endian (e.g., compatible with x86 systems) 举例：
>>> 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 描述 2 The default, output 2D WKB. 3 Output 3D WKB. 举例：
>>> 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'


class
WKTWriter
(dim=2, trim=False, precision=None)¶ This class allows outputting the WKT representation of a geometry. See the
WKBWriter.outdim
,trim
, andprecision
attributes for details about the constructor arguments.
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
¶ 查看
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)'

脚注
[1]  See PostGIS EWKB, EWKT and Canonical Forms, PostGIS documentation at Ch. 4.1.2. 