OGR Simple Feature Library

ABT 182 / HYD 182

Environmental Analysis using GIS

Week 4-2

OGR

Command line program

Library (python, R, QGIS, ….)

Supports many different vector formats

Shapefiles, personal geodatabases, MapInfo, GRASS, KML

Databases such as MySQL, PostgreSQL, Oracle Spatial

try: from osgeo import ogrexcept: import ogr

http://www.gdal.org/ogr/

A driver knows a certain data typefrom osgeo import ogr

driver = ogr.GetDriverByName('ESRI Shapefile')

dataSource = driver.Open(fn, 0)

layer = dataSource.GetLayer(0)print layer.GetFeatureCount()print layer.GetExtent()

feature = layer.GetNextFeature()while feature:

id = feature.GetField('id')geom = feature.GetGeometryRef()print geom.GetX()feature.Destroy()feature = layer.GetNextFeature()

datasource.Destroy()

0 for read-only, 1 for writeable

first layer (shp only has one)

very similar to Arc scripts

for point objects

Reading a file with OGR

Writing a file with OGR

dataSource = driver.Open(fn, 1)

layer = dataSource.GetLayer(0)

driver = ogr.GetDriverByName('ESRI Shapefile')

if os.path.exists(fn):driver.DeleteDataSource(fn)

dataSource = driver.CreateDataSource(fn)

layer = dataSource.CreateLayer('test', geom_type=ogr.wkbPoint)

Open an existing file

Create a new file

os.chdir('c:/abt182/lab8/')fn = 'test.shp'

fieldDefn = ogr.FieldDefn('id', ogr.OFTInteger)

fieldDefn = ogr.FieldDefn('id', ogr.OFTString)fieldDefn.SetWidth(4)

Defining new fieldsFrom an existing feature

fieldDefn = feature.GetFieldDefnRef(0)

fieldDefn = feature.GetFieldDefnRef('id')

layer.CreateField(fieldDefn)

From a new feature

featureDefn = layer.GetLayerDefn()

feature = ogr.Feature(featureDefn)

feature.SetGeometry(<object>)

feature.SetField('id', 23)

layer.CreateFeature(feature)

Creating new features(after adding the fields)