Introduction

PyGeoIf provides a GeoJSON-like protocol for geo-spatial (GIS) vector data.

see https://gist.github.com/2217756

Other Python programs and packages that you may have heard of already implement this protocol:

• ArcPy http://help.arcgis.com/en/arcgisdesktop/
• descartes https://bitbucket.org/sgillies/descartes/
• geojson http://pypi.python.org/pypi/geojson/
• PySAL http://pysal.geodacenter.org/
• Shapely https://github.com/Toblerity/Shapely
• pyshp https://pypi.python.org/pypi/pyshp

So when you want to write your own geospatial library with support for this protocol you may use pygeoif as a starting point and build your functionality on top of it

You may think of pygeoif as a 'shapely ultralight' which lets you construct geometries and perform very basic operations like reading and writing geometries from/to WKT, constructing line strings out of points, polygons from linear rings, multi polygons from polygons, etc. It was inspired by shapely and implements the geometries in a way that when you are familiar with shapely you feel right at home with pygeoif

It was written to provide clean and python only geometries for fastkml

PyGeoIf is continually tested with Travis CI

Example

>>> from pygeoif import geometry
>>> p = geometry.Point(1,1)
>>> p.__geo_interface__
{'type': 'Point', 'coordinates': (1.0, 1.0)}
>>> print p
POINT (1.0 1.0)
>>> p1 = geometry.Point(0,0)
>>> l = geometry.LineString([p,p1])
>>> l.bounds
(0.0, 0.0, 1.0, 1.0)
>>> dir(l)
['__class__', '__delattr__', '__dict__', '__doc__', '__format__',
'__geo_interface__', '__getattribute__', '__hash__', '__init__',
'__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__',
'__setattr__', '__sizeof__', '__str__', '__subclasshook__',
'__weakref__', '_coordinates', '_geoms', '_type', 'bounds', 'coords',
'geom_type', 'geoms', 'to_wkt']
>>> print l
LINESTRING (1.0 1.0, 0.0 0.0)

You find more examples in the test_main.py file which cover every aspect of pygeoif or in fastkml.

Classes

All classes implement the attribute:

• __geo_interface__: as dicussed above

All geometry classes implement the attributes:

• geom_type: Returns a string specifying the Geometry Type of the object
• bounds: Returns a (minx, miny, maxx, maxy) tuple (float values) that bounds the object.
• wkt: Returns the 'Well Known Text' representation of the object

and the method:

• to_wkt which also prints the object

GeoObject

Base class for Geometry, Feature, and FeatureCollection

Geometry

Base class for geometry objects. Inherits from Geoobject.

Point

A zero dimensional geometry

A point has zero length and zero area.

Attributes

x, y, z : float

Coordinate values

Example

>>> p = Point(1.0, -1.0)
>>> print p
POINT (1.0000000000000000 -1.0000000000000000)
>>> p.y
-1.0
>>> p.x
1.0

LineString

A one-dimensional figure comprising one or more line segments

A LineString has non-zero length and zero area. It may approximate a curve and need not be straight. Unlike a LinearRing, a LineString is not closed.

Attributes

geoms : sequence

A sequence of Points

LinearRing

A closed one-dimensional geometry comprising one or more line segments

A LinearRing that crosses itself or touches itself at a single point is invalid and operations on it may fail.

A Linear Ring is self closing

Polygon

A two-dimensional figure bounded by a linear ring

A polygon has a non-zero area. It may have one or more negative-space "holes" which are also bounded by linear rings. If any rings cross each other, the geometry is invalid and operations on it may fail.

Attributes

exterior : LinearRing

The ring which bounds the positive space of the polygon.

interiors : sequence

A sequence of rings which bound all existing holes.

MultiPoint

A collection of one or more points

Attributes

geoms : sequence

A sequence of Points

MultiLineString

A collection of one or more line strings

A MultiLineString has non-zero length and zero area.

Attributes

geoms : sequence

A sequence of LineStrings

MultiPolygon

A collection of one or more polygons

Attributes

geoms : sequence

A sequence of Polygon instances

GeometryCollection

A heterogenous collection of geometries (Points, LineStrings, LinearRings and Polygons)

Attributes

geoms : sequence

A sequence of geometry instances

Please note: GEOMETRYCOLLECTION isn't supported by the Shapefile format. And this sub-class isn't generally supported by ordinary GIS sw (viewers and so on). So it's very rarely used in the real GIS professional world.

Example

>>> from pygeoif import geometry
>>> p = geometry.Point(1.0, -1.0)
>>> p2 = geometry.Point(1.0, -1.0)
>>> geoms = [p, p2]
>>> c = geometry.GeometryCollection(geoms)
>>> c.__geo_interface__
{'type': 'GeometryCollection', 'geometries': [{'type': 'Point', 'coordinates': (1.0, -1.0)},/
{'type': 'Point', 'coordinates': (1.0, -1.0)}]}
>>> [geom for geom in geoms]
[Point(1.0, -1.0), Point(1.0, -1.0)]

Feature

Aggregates a geometry instance with associated user-defined properties.

Attributes

geometry : object

A geometry instance

properties : dict

A dictionary linking field keys with values associated with with geometry instance

Example

>>> p = Point(1.0, -1.0)
>>> props = {'Name': 'Sample Point', 'Other': 'Other Data'}
>>> a = Feature(p, props)
>>> a.properties
{'Name': 'Sample Point', 'Other': 'Other Data'}
>>> a.properties['Name']
'Sample Point'

FeatureCollection

A heterogenous collection of Features

Attributes

features: sequence

A sequence of feature instances

Example

>>> from pygeoif import geometry
>>> p = geometry.Point(1.0, -1.0)
>>> props = {'Name': 'Sample Point', 'Other': 'Other Data'}
>>> a = geometry.Feature(p, props)
>>> p2 = geometry.Point(1.0, -1.0)
>>> props2 = {'Name': 'Sample Point2', 'Other': 'Other Data2'}
>>> b = geometry.Feature(p2, props2)
>>> features = [a, b]
>>> c = geometry.FeatureCollection(features)
>>> c.__geo_interface__
{'type': 'FeatureCollection', 'features': [{'geometry': {'type': 'Point', 'coordinates': (1.0, -1.0)},/
 'type': 'Feature', 'properties': {'Other': 'Other Data', 'Name': 'Sample Point'}},/
 {'geometry': {'type': 'Point', 'coordinates': (1.0, -1.0)}, 'type': 'Feature',/
 'properties': {'Other': 'Other Data2', 'Name': 'Sample Point2'}}]}
>>> [feature for feature in c]
[<Feature Instance Point geometry 2 properties>, <Feature Instance Point geometry 2 properties>]

Functions

as_shape

Create a pygeoif feature from an object that provides the __geo_interface__

>>> from shapely.geometry import Point
>>> from pygeoif import geometry
>>> geometry.as_shape(Point(0,0))
<pygeoif.geometry.Point object at 0x...>

from_wkt

Create a geometry from its WKT representation

>>> p = geometry.from_wkt('POINT (0 1)')
>>> print p
POINT (0.0 1.0)

signed_area

Return the signed area enclosed by a ring using the linear time algorithm at http://www.cgafaq.info/wiki/Polygon_Area. A value >= 0 indicates a counter-clockwise oriented ring.

orient

Returns a copy of the polygon with exterior in counter-clockwise and interiors in clockwise orientation for sign=1.0 and the other way round for sign=-1.0

mapping

Returns the __geo_interface__ dictionary

Development

Installation

You can install PyGeoIf from pypi using pip:

pip install pygeoif

Testing

In order to provide a Travis-CI like testing of the PyGeoIf package during development, you can use tox (pip install tox) to evaluate the tests on all supported Python interpreters which you have installed on your system.

You can run the tests with tox --skip-missin-interpreters and are looking for output similar to the following:

______________________________________________________ summary ______________________________________________________
SKIPPED:  py26: InterpreterNotFound: python2.6
  py27: commands succeeded
SKIPPED:  py32: InterpreterNotFound: python3.2
SKIPPED:  py33: InterpreterNotFound: python3.3
  py34: commands succeeded
SKIPPED:  pypy: InterpreterNotFound: pypy
SKIPPED:  pypy3: InterpreterNotFound: pypy3
  congratulations :)

You are primarily looking for the congratulations :) line at the bottom, signifying that the code is working as expected on all configurations available.