# Τεκμηρίωση του Django - 1.10.7

# 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 high-level Python wrapper for the GEOS library, its features include:

- A BSD-licensed interface to the GEOS geometry routines, implemented purely in Python using `ctypes`.
- Loosely-coupled to GeoDjango. For example, `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.
- Mutability: `GEOSGeometry` objects may be modified.
- Cross-platform and tested; compatible with Windows, Linux, Solaris, and Mac OS X 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'))

My logs are filled with GEOS-related errors

You find many `TypeError` or `AttributeError` exceptions filling your Web server’s log files. This generally means that you are creating GEOS objects at the top level of some of your Python modules. Then, due to a race condition in the garbage collector, your module is garbage collected before the GEOS object. To prevent this, create `GEOSGeometry` objects inside the local scope of your functions/methods.

### 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] # 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:

    >>> from django.contrib.gis.geos import LineString
    >>> ls1 = LineString((0, 0), (1, 1))
    >>> ls2 = LineString((1, 1), (0, 0))
    >>> ls1.equals(ls2)
    True
    >>> ls1 == ls2
    False

## Geometry Objects

### `GEOSGeometry`

class `GEOSGeometry`(geo_input, srid=None)

  Παράμετροι: | 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 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 (requires GDAL) | `str` or `unicode`

#### Properties

`GEOSGeometry.``coords`

  Returns the coordinates of the geometry as a tuple.

`GEOSGeometry.``dims`

  Returns the dimension of the geometry:

  - `0` for `Point`s and `MultiPoint`s
  - `1` for `LineString`s and `MultiLineString`s
  - `2` for `Polygon`s and `MultiPolygon`s
  - `-1` for empty `GeometryCollection`s
  - the maximum dimension of its elements for non-empty `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 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

#### 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” 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)`.

  Σημείωση

  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.

  Σημείωση

  Requires GDAL.

`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.

#### 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` 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:

  - Every point of the other geometry is a point of this geometry.
  - The DE-9IM 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. 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***`.

#### 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 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.

#### 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 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:

  - 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 a `Polygon` or `MultiPolygon` geometry (unlike `GEOSGeometry.union()`, which may return geometries of lower dimension if a topology collapse occurs).

#### 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 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).

  Σημείωση

  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`.

  Σημείωση

  Requires GDAL.

`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.

  Σημείωση

  Requires GDAL. 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.

### `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([])

  In previous versions, an empty `Point` couldn’t be instantiated.

### `LineString`

class `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`

class `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`

class `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.

  classmethod `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

## Geometry Collections

### `MultiPoint`

class `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`

class `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`

class `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`

    Αποσύρθηκε στην έκδοση 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`

class `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.

## Prepared Geometries

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

### `PreparedGeometry`

class `PreparedGeometry`

  All methods on `PreparedGeometry` take an `other` argument, which must be a `GEOSGeometry` instance.

  `contains`(other)
  `contains_properly`(other)
  `covers`(other)
  `crosses`(other)
  `disjoint`(other)
  `intersects`(other)
  `overlaps`(other)
  `touches`(other)
  `within`(other)

## Geometry Factories

`fromfile`(file_h)

  Παράμετροι: | file_h (a Python `file` object or a string path to the file) – input file that contains spatial data
  Επιστρεφόμενος τύπος:
  | 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)

  Παράμετροι: | string (string) – string that contains spatial data srid (int) – spatial reference identifier
  Επιστρεφόμενος τύπος:
  | a `GEOSGeometry` corresponding to the spatial data in the string

  `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)

## I/O Objects

### Reader Objects

The reader I/O classes simply return a `GEOSGeometry` instance from the WKB and/or WKT input given to their `read(geom)` method.

class `WKBReader`

  Example:

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

class `WKTReader`

  Example:

      >>> 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 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'

class `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.

## Settings

### `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`).

Σημείωση

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`.

## Exceptions

exception `GEOSException`

  The base GEOS exception, indicates a GEOS-related error.