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pygeoif 0.3.0dev

A basic implementation of the __geo_interface__

Latest Version: 0.4.1

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:

So when you want to write your own geospatilal 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

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 tests.py file which cover every aspect of pygeoif or in fastkml.

Classes

All classes implement the attributes:

  • __geo_interface__: as dicussed above
  • 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

Point

A zero dimensional feature

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 feature 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 feature 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.

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

Changelog

0.3 (2012/11/14)

  • add GeometryCollection
  • len(Multi*) and len(GeometryCollection) returns the number of contained Geometries
  • add orient function to get clockwise or counterclockwise oriented poygons
  • add signed_area function
  • add _set_orientation method to lineStrings, Polygons and MultiPolygons

0.2.1 (2012/08/02)

  • as_shape also accepts an object that is neither a dictionary nor has a __geo_interface__ but can be converted into a __geo_interface__ compliant dictionary

0.2 (2012/08/01)

  • change license to LGPL
  • add wkt as a property
  • as_shape also accepts a __geo_interface__ compliant dictionary
  • test with python3

0.1 (2012/07/27)

  • initial release
 
File Type Py Version Uploaded on Size
pygeoif-0.3.0dev.tar.gz (md5) Source 2012-11-14 26KB
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