Pycon 2012 Taiwan - [Download PDF]

那些年Python攻佔GIS The Year Python Takes Over GIS

鄧東波 Dongpo Deng中央研究院資訊科學研究所

﹠胡崇偉 marr, Tsung Wei Hu中央研究院人文社會科學中心

PyCon 2012

Saturday, June 9, 2012

Content

• Introduction - GIS and why GIS uses python

• Python-blinding core geospatial libraries

• the use of python in Desktop GISs

• Web application framework for geospatial

Saturday, June 9, 2012

What is GIS?• GIS is stand for Geographic

Information System

• integrates hardware, software, and data for capturing, managing, analyzing, and displaying geospatial data.

• allows people to use methods for understanding, interpreting, and visualizing relationships and patterns of geospatial data

Saturday, June 9, 2012

Why Geospatial domain uses Python

• Easy to learn

• Code is readable

• Large community

• Easy interaction with C and Java libraries

• Many existing modules and packages

• core geospatial libraries

• map rendering

• database

• web server

Picture from http://pypi.python.org/pypi/collective.geo.bundle

Saturday, June 9, 2012

http://pypi.python.org/pypi/collective.geo.bundle

Why Geospatial domain uses Python

• Easy to learn

• Code is readable

• Large community

• Easy interaction with C and Java libraries

• Many existing modules and packages

• core geospatial libraries

• map rendering

• database

• web server

Picture from http://pypi.python.org/pypi/collective.geo.bundle

Saturday, June 9, 2012

http://pypi.python.org/pypi/collective.geo.bundle

Geospatial development tasks

• Visualizing geospatial data

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Geospatial development tasks

• Analyzing geospatial data

• e.g. How many people should escape as Kuosheng nuclear power plant (核二廠) explodes?

• Create a geospatial mashup

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The geospatial development tasks involve

• Math- analytic geometry

• e.g.Euclidean geometry

• Computer graphics (rendering)

• e.g. rending, visualizing

• Database

• General Search Tree (GiST)

• open geospatial standards,

• e.g. GML, WKT

Saturday, June 9, 2012

Python libraries for geospatial development

• Reading/ Writing geospatial data

• GDAL/OGR

• Dealing with Projections

• pyproj

• Analyzing and manipulating geospatial data

• Shapely

• Visualizing geospatial data

• Mapnik

Saturday, June 9, 2012

GDAL (Geospatial Data Abstraction Library)

from osgeo import gdal,gdalconstimport structdataset = gdal.Open("DEM.dat")band = dataset.GetRasterBand(1)fmt = "<" + ("h" * band.XSize)totHeight = 0for y in range(band.YSize): scanline = band.ReadRaster(0, y, band.XSize, 1, band.XSize, 1,band.DataType) values = struct.unpack(fmt, scanline) for value in values: totHeight = totHeight + valueaverage = totHeight / (band.XSize * band.YSize)print "Average height =", average

• read through it one scanline at a time from file

• use the struct standard Python library module to read the individual values out of the scanline.

• Each value corresponds to the height of that point, in meters

Source from: Westra, 2010, Python Geospatial DevelopmentSaturday, June 9, 2012

OGR(OpenGIS Simple Features Reference Implementation)

• uses OGR to read through the contents of a Shapefile,

• printing out the value of the NAME attribute for each feature, along with the geometry type

from osgeo import ogr

shapefile = ogr.Open("TM_WORLD.shp")

layer = shapefile.GetLayer(0)

for i in range(layer.GetFeatureCount()):

feature = layer.GetFeature(i)

name = feature.GetField("NAME")

geometry = feature.GetGeometryRef()

print i, name, geometry.GetGeometryName()

Source from: Westra, 2010, Python Geospatial DevelopmentSaturday, June 9, 2012

PyProj• a location specified using UTM zone 17 coordinates.

• Using two Proj objects to define the UTM Zone 17 and lat/long projections

• translates this location's coordinates into latitude and longitude values

import pyproj

UTM_X = 565718.523517

UTM_Y = 3980998.9244

srcProj = pyproj.Proj(proj="utm", zone="11",

ellps="clrk66", units="m")

dstProj = pyproj.Proj(proj='longlat', ellps='WGS84',

datum='WGS84')

long,lat = pyproj.transform(srcProj, dstProj, UTM_X, UTM_Y)

print "UTM zone 17 coordinate (%0.4f, %0.4f) = %0.4f, %0.4f" %

(UTM_X, UTM_Y, lat, long)Source from: Westra, 2010, Python Geospatial Development

Saturday, June 9, 2012

Shapely GEOS

import shapely.geometrypt = shapely.geometry.Point(0, 0)circle = pt.buffer(1.0)square = shapely.geometry.Polygon([(0, 0), (1, 0), (1, 1), (0, 1), (0, 0)])intersect = circle.intersection(square)for x,y in intersect.exterior.coords: print x,y

Source from: Westra, 2010, Python Geospatial DevelopmentSaturday, June 9, 2012

Mapnik

• Mapnik is an open source mapping toolkit for desktop- and server-based map rendering, written in C++.

• there are Python bindings to facilitate fast-paced agile development.

• OpenStreetMap project (OSM) uses Mapnik in combination with an Apache Web Server module (mod_tile) to render tiles that make up the OSM 'Slippy Map' Layer.

Source from: Westra, 2010, Python Geospatial Development

Saturday, June 9, 2012

http://en.wikipedia.org/wiki/Open_source

http://en.wikipedia.org/wiki/Mapping

http://en.wikipedia.org/wiki/Rendering_%28computer_graphics%29

http://en.wikipedia.org/wiki/C%2B%2B

http://en.wikipedia.org/wiki/OpenStreetMap

http://en.wikipedia.org/wiki/Apache_Web_Server