Pycon 2012 Taiwan
27
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
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Transcript of Pycon 2012 Taiwan
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
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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
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
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
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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
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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
Mapnikimport mapnik
symbolizer = mapnik.PolygonSymbolizer(
mapnik.Color("darkgreen"))
rule = mapnik.Rule()
rule.symbols.append(symbolizer)
style = mapnik.Style()
style.rules.append(rule)
layer = mapnik.Layer("mapLayer")
layer.datasource = mapnik.Shapefile(
file="TW_village.shp")
layer.styles.append("mapStyle")
map = mapnik.Map(800, 400)
map.background = mapnik.Color("steelblue")
map.append_style("mapStyle", style)
map.layers.append(layer)
map.zoom_all()
mapnik.render_to_file(map, "map.png", "png")
Saturday, June 9, 2012
Desktop GIS
Pic from http://www.pressebox.de/attachments/details/39739
Saturday, June 9, 2012
Script Languages in ESRI family
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ArcPy• ArcPy is a package for performing geographic data
analysis, data conversion, data management, and map automation in ArcGIS with Python.
• ArcPy includes three modules:
• mapping module (arcpy.mapping)
• Spatial analyst module (arcpy.sa)
• Geostatistical analyst module (arcpy.ga)
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/What_is_ArcPy/
ArcGIS ArcPy Python
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arcpy in ArcGIS 10
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Python in QGIS
• There’s a number of ways to access the layers in QGIS.
• Each way starts by first referencing the QgisInterface class which is called iface in the Python bindings.
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Example
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GeoDjango
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http://140.109.160.129:8000/admin/world/worldborders/Saturday, June 9, 2012
Remarks
• There are many Python libraries or applications for geospatial purposes
• Python is increasing its value in geospatial domain
• Will Python take over GIS? .....Let’s see!
Saturday, June 9, 2012
