Why use open source?
Advantages
1. Free, suitable for individuals and small companies
2. Powerful development tools, easier to find bugs
3. Cross-platform, can be used on windows and Linux
4. Stunning!
Disadvantages
1. No built-in geoprocessor
2. Few people use it
Open source RS/GIS module
1. OGR vector library: simple vector data reading and writing, is part of GDAL
2. GDAL geospatial data abstraction library:
a) Reading and writing raster data
b) ArcGIS is also developed based on GDAL
c) C++ library, but you can use python to call
related modules
1. Numeric: High-speed array processing is especially important for raster data
2. NumPy: the next generation of Numeric
3. A more powerful gis library http://www.gispython.org/
Import library:
import ogr
Or:
from osgeo import ogr
The universal method is:
try:
from osgeo import ogr
except:
import ogr
To read a certain type of data, it must be loaded first Data-driven means initializing an object so that it "knows" a certain data structure.
import ogr
driver = ogr.GetDriverByName('ESRI Shapefile')
The open() method of the data-driven driver returns a data source object
open(
where update 0 means read-only, 1 means writable. For example:
from osgeo import ogr
driver = ogr.GetDriverByName('ESRI Shapefile')
filename = 'C:/Users/gongwei/Documents/My eBooks /python_and_sage/GDAL python/test/ospy_data1/sites.shp'
dataSource = driver.Open(filename,0)
if dataSource is None:
print 'could not open'
sys.exit(1)
print 'done!'
Note that filename must be an absolute path!
Because absolute paths must be used, in order to simplify the code, os.chdir() is often used
to read the data layer
layer = dataSource.GetLayer(0)
Generally, ESRI shapefiles are filled with 0. If not filled in, the default is 0.
Look at how many points there are in this data layer?
n = layer.GetFeatureCount()
print 'feature count:', n
Read the upper, lower, left and right boundaries
extent = layer.GetExtent()
print 'extent:', extent
print 'ul: ', extent[0], extent[3]
print 'lr:', extent[1], extent[2]
Read a certain element feature (finally get to the point), what is read here is a point #should be a different id
print fid
In addition, read features in order and loop through all features
feat = layer.GetNextFeature() #Read the next
while feat:
feat = layer.GetNextFeature ()
later.ResetReading() #Reset
Extract the geometry of the feature
geom = feat.GetGeometryRef()
geom.GetX()
geom.GetY()
print geom.
Release memory
feature.Destroy()
Close the data source, which is equivalent to closing the file in file system operations
dataSource.Destroy()
Let’s talk about how to write it after reading it
Create a new file
driver.CreateDataSource( But this file cannot already exist, otherwise an error will occur Create a new layer dataSource.CreateLayer( For example: ds2 = driver.CreateDataSource('test.shp') layer2 = ds2.CreateLayer('test', geom_type=ogr.wkbPoint) To delete a shp file driver.DeleteDataSource ('test.shp') To add a new field, it can only be added in the layer, and there cannot be data. If the added field is a string, the width must be set fieldDefn = ogr.FieldDefn( 'id', ogr.OFTString) fieldDefn.SetWidth(4) layer.CreateField(fieldDefn) To add a new feature, you must first complete the previous step and add all the fields and then start from layer Read the corresponding feature type in and create feature featureDefn = layer.GetLayerDefn() feature = ogr.Feature(featureDefn) Set the geometric shape feature.SetGeometry(point) Set a certain field The value of feature.SetField('id', 23) Write the feature into layer layer.CreateFeature(feature) The above is the content of the python gdal tutorial: using ogr to read and write vector data. For more related content, please pay attention to the PHP Chinese website (www.php.cn)!