geography

PyGeoj – A simple Python Geojson file reader and writer.

geojson

Just wrapped up a new library called PyGeoj that makes it a breeze to read and write geojson as files. By treating geojson as an actual fileformat instead of just as a set of formatting rules, the aim was that PyGeoj should make it just as easy to deal with .geojson files as with .shp files — sort of like the PyShp for Geojson data.

Since the arrival of the Geojson format, there has been an increasing ability to send and receive geometry types between different libraries when doing Python GIS programming. As useful as this is, it seems to me that this has made geojson more of an inter-library communication language than an actual file-format (like the shapefile). Using the built-in json library and playing with the geojson dictionary directly is one option, using the python-geojson library is another, but both require a fairly intimate knowledge of the format specification (ie more suitable for developers than actual end-users).

PyGeoj focuses on only a few basic classes, and hopefully intuitive attributes and methods. As such, loading a file can be done with:

       testfile = pygeoj.load(“testfile.geojson”)

Resulting in a file instance whose file-information like “crs” or “bbox” and features can be accessed, edited, and eventually saved:

      print testfile.bbox
      for feature in testfile:
             print feature.properties
      testfile.save(“testfile_copy.geojson”)

Although geojson is generally slower and more memory consuming than the shapefile format, PyGeoj will hopefully encourage use of the geojson format for everyday-tasks or sending data to other libraries across “long distances” (eg online).

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Shapy – A new pure-Python Shapely in the works

ImageOver the matter of the last few days, I was working on understanding the pure-Python version of Angus Johnson’s polygon Clipper library (that would be me to the right about now). As I got it working and wanted an easy way to test it I began adding more and more functionality, and before I knew it turned out to be quite solid and useful.

The package I ended up writing consiImagests of a bunch of geometrical
shape objects that the user can
create, measure, and manipulate with operations like intersect, union, distance, etc, which uses Angus’ Clipper and some of my own code in the background. This might sound a lot like the Sean Gillies’ Shapely library, and that’s fine because I modeled it directly on its geometry
types, attribute names, and methods. And hence the name Shapy
– a “lighter” pure-Python version of Shapely.

Some additional cool features are:

  • All shape types support the __geo_interface__ attribute so they can easily be sent to and used with other packages.
  • Shapes can be automatically created from any Python object that has the Image__geo_interface__ attribute.
  • And most but not least, a .view() method will visualize the shape for you, without having to think about imaging library dependencies, since Shapy comes packaged along with my other pure-Python PyDraw module. This is especially cool since you can for instance use the pure-Python PyShp shapefile reader to loop through shapes and instantly view each shape up close, since the shapes have the __geo_interface__ protocol.

Note though that Shapy is still in the works and lacks some features, but it can be used for very basic playing around with. See the docs on the Github page for more info on what’s currently supported, and available commands.

I would love contributions or suggestions on this one, since we’re dealing with quite advanced geometrical operations and vector math. Eventually it will probably need some optimization as well, but for now I just want to get it up and running with the basics.

Introducing a Pure-Python Quadtree Spatial Index for GIS-use

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I just finished writing a quadtree spatial index package in pure python which is aimed for GIS use.

Spatial index packages for Python already exist, a popular one being the Rtree package, which comes in both a C and pure-Python variety. In comparison to Rtree indexes however, QuadTree indexes are supposedly preferable over Rtree indexes when the index has to be updated often. I only know of one QuadTree index package for Python, but that one was last updated in 2004, so I’m not sure if it is compatible with newer versions of Python, and it has to be compiled.

And so I threw together the pure-Python PyQuadTree package; for portable and easy-install uses, and when heavy updates to the index is expected. In reality I didn’t really make the quadtree index code, that credit goes to Matt Rasmussen’s original Quadtree code. What I did was I added support for irregularly shaped quad trees instead of only squares, and simplified the front-end user functions for GIS users. The API syntax is purposely made very similar to the Rtree package and so should be familiar to users of that package. Exact guidelines for how to use it is found on the Github package page linked to below.

Click here to go the Github page where you can download and try the package.

GeoVis v0.2.0 – Tons of New Features

A major new update of the GeoVis map-making library is now available.

Image

New features in v0.2.0 include:

  • Attribute classification with legend (categorical, equal classes, equal interval, natural breaks)
  • Render points as circle, square, or pyramid
  • Map zooming
  • Customize map with basic shapes and text
  • And more . . .

Check out all new features, full documentation, and examples from the code repository at GitHub.

First Milestone Reached: The Visualizing Library is Now Complete!

readme_topbanner

The first milestone in our journey has been reached! I just completed the visualizing library for viewing your shapefiles. It is very easy to install, simple to use, and can be used in many flexible ways. I have written more about it elsewhere, and besides the project GitHub frontpage describes and documents it quite well, so I will not go into depth about it right now. So you can either check it out from the Downloads page, or go directly to its Github repository.

And the Challenge Begins!

Hilly Road

The Python-GIS Challenge is a series of open-source projects to connect and integrate many of Python’s existing spatial extensions into a single easy-to-use library. Each project will focus on a particular GIS-related field and will be made available for free download once it is completed. This website will document the progress, challenges, and setbacks experienced along this journey.