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Programmatically populating shapefile field with polygon areas in OGR?

Need help assigning values to field using OGR in pythonPopulating new field in shapefile with values from list?Getting Field value for a given coordinate out of ESRI Shapefile using GDAL/OGRNeed help assigning values to field using OGR in pythonOGR - Weird GeomType -2147483645 on polygon shapefilePython Band.SetNoDataValue(), sets all bands at oncePolygon overlaps on “Merge Shapefile”Intersect polyline and polygon with ogrWrite coordinates to new shp file columns with OGRExtracting coordinates from multipoint geometries?OGR multipolygon with holes modelPopulating new field in shapefile with values from list?

6

3

I'm trying to programmatically populate a shp field with polygon areas:

import sys

import ogr



ds = ogr.Open( 'tttttttttt.shp', update = 1 )

if ds is None:

    print "Open failed./n"

    sys.exit( 1 )



lyr = ds.GetLayerByName( "tttttttttt" )

lyr.ResetReading()



field_defn = ogr.FieldDefn( "Area", ogr.OFTReal )

lyr.CreateField(field_defn)



for i in lyr:

    # feat = lyr.GetFeature(i) 

    geom = i.GetGeometryRef()

    area = geom.GetArea()

    print 'Area =', area

    lyr.SetFeature(i)

    i.SetField( "Area", area )



ds = None

But I get an empty values in the field...

python shapefile ogr polygon-creation

share|improve this question

edited 35 mins ago

PolyGeo♦

53.5k1780240

asked Sep 28 '12 at 15:39

vascobnunesvascobnunes

2,79283766

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Can you share a dummy shape file?
  
  – R.K.
  Sep 28 '12 at 15:52
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  how do I share it? email?
  
  – vascobnunes
  Sep 28 '12 at 15:58
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  dropbox.com/sh/b5uyzqf7oowsv8e/lL9bHRHTCT
  
  – vascobnunes
  Sep 28 '12 at 16:00
  

  
  
  
  

add a comment | 

6

3

I'm trying to programmatically populate a shp field with polygon areas:

import sys

import ogr



ds = ogr.Open( 'tttttttttt.shp', update = 1 )

if ds is None:

    print "Open failed./n"

    sys.exit( 1 )



lyr = ds.GetLayerByName( "tttttttttt" )

lyr.ResetReading()



field_defn = ogr.FieldDefn( "Area", ogr.OFTReal )

lyr.CreateField(field_defn)



for i in lyr:

    # feat = lyr.GetFeature(i) 

    geom = i.GetGeometryRef()

    area = geom.GetArea()

    print 'Area =', area

    lyr.SetFeature(i)

    i.SetField( "Area", area )



ds = None

But I get an empty values in the field...

python shapefile ogr polygon-creation

share|improve this question

edited 35 mins ago

PolyGeo♦

53.5k1780240

asked Sep 28 '12 at 15:39

vascobnunesvascobnunes

2,79283766

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Can you share a dummy shape file?
  
  – R.K.
  Sep 28 '12 at 15:52
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  how do I share it? email?
  
  – vascobnunes
  Sep 28 '12 at 15:58
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  dropbox.com/sh/b5uyzqf7oowsv8e/lL9bHRHTCT
  
  – vascobnunes
  Sep 28 '12 at 16:00
  

  
  
  
  

add a comment | 

I'm trying to programmatically populate a shp field with polygon areas:

import sys

import ogr



ds = ogr.Open( 'tttttttttt.shp', update = 1 )

if ds is None:

    print "Open failed./n"

    sys.exit( 1 )



lyr = ds.GetLayerByName( "tttttttttt" )

lyr.ResetReading()



field_defn = ogr.FieldDefn( "Area", ogr.OFTReal )

lyr.CreateField(field_defn)



for i in lyr:

    # feat = lyr.GetFeature(i) 

    geom = i.GetGeometryRef()

    area = geom.GetArea()

    print 'Area =', area

    lyr.SetFeature(i)

    i.SetField( "Area", area )



ds = None

But I get an empty values in the field...

python shapefile ogr polygon-creation

share|improve this question

edited 35 mins ago

PolyGeo♦

53.5k1780240

asked Sep 28 '12 at 15:39

vascobnunesvascobnunes

2,79283766

import sys

import ogr



ds = ogr.Open( 'tttttttttt.shp', update = 1 )

if ds is None:

    print "Open failed./n"

    sys.exit( 1 )



lyr = ds.GetLayerByName( "tttttttttt" )

lyr.ResetReading()



field_defn = ogr.FieldDefn( "Area", ogr.OFTReal )

lyr.CreateField(field_defn)



for i in lyr:

    # feat = lyr.GetFeature(i) 

    geom = i.GetGeometryRef()

    area = geom.GetArea()

    print 'Area =', area

    lyr.SetFeature(i)

    i.SetField( "Area", area )



ds = None

share|improve this question

edited 35 mins ago

PolyGeo♦

53.5k1780240

asked Sep 28 '12 at 15:39

vascobnunesvascobnunes

2,79283766

share|improve this question

edited 35 mins ago

PolyGeo♦

53.5k1780240

asked Sep 28 '12 at 15:39

vascobnunesvascobnunes

2,79283766

edited 35 mins ago

PolyGeo♦

53.5k1780240

edited 35 mins ago

PolyGeo♦

53.5k1780240

asked Sep 28 '12 at 15:39

vascobnunesvascobnunes

2,79283766

asked Sep 28 '12 at 15:39

vascobnunesvascobnunes

2,79283766

1 Answer
1

active

oldest

votes

15

You have to use lyr.SetFeature(i) to trigger the update in your shape file.
You'll have to close the data sources in the end so things get written.

import sys

import ogr



ds = ogr.Open( 'tttttttttt.shp', update = 1 )

if ds is None:

    print "Open failed./n"

    sys.exit( 1 )



lyr = ds.GetLayerByName( "tttttttttt" )

lyr.ResetReading()



field_defn = ogr.FieldDefn( "Area", ogr.OFTReal )

lyr.CreateField(field_defn)



for i in lyr:

    # feat = lyr.GetFeature(i) 

    geom = i.GetGeometryRef()

    area = geom.GetArea()

    print 'Area =', area

    lyr.SetFeature(i)

    i.SetField( "Area", area )

    lyr.SetFeature(i)

ds = None

*Low-rep comment and concern: If the 'Area' field already exists, this code creates an extra field, like "Area_n", and overwrites the existing Area field. Maybe folks should add some safety code like:

ldef = lyr.GetLayerDefn()

if ldef.GetFieldIndex("Area") != -1:

    print "'Area' field already defined"

    ... # exit or overwrite logic

share|improve this answer

edited Mar 4 '13 at 21:23

Dave X

840517

answered Sep 28 '12 at 15:51

R.K.R.K.

15.9k351105

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You're welcome. An upvote would be nice, too ;-)
  
  – R.K.
  Sep 28 '12 at 16:15
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I have similar project in .net,code is similar as well.In your code you mentioned that after SetField method,should use SetFeature in order to update layer.Unfortunately that doesn't work.Any ideas ?
  
  – Myra
  Feb 6 '13 at 6:37
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Myra You might want to ask that on a separate question. Unfortunately, I'm not really familiar with .NET. Hopefully, others can help you. Just post the question :)
  
  – R.K.
  Feb 21 '13 at 15:19
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Great, wonder why "SetFeature" is mentioned nowhere in the docs...
  
  – adamczi
  Jul 11 '18 at 21:00
  

  
  
  
  

add a comment | 

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15

You have to use lyr.SetFeature(i) to trigger the update in your shape file.
You'll have to close the data sources in the end so things get written.

import sys

import ogr



ds = ogr.Open( 'tttttttttt.shp', update = 1 )

if ds is None:

    print "Open failed./n"

    sys.exit( 1 )



lyr = ds.GetLayerByName( "tttttttttt" )

lyr.ResetReading()



field_defn = ogr.FieldDefn( "Area", ogr.OFTReal )

lyr.CreateField(field_defn)



for i in lyr:

    # feat = lyr.GetFeature(i) 

    geom = i.GetGeometryRef()

    area = geom.GetArea()

    print 'Area =', area

    lyr.SetFeature(i)

    i.SetField( "Area", area )

    lyr.SetFeature(i)

ds = None

*Low-rep comment and concern: If the 'Area' field already exists, this code creates an extra field, like "Area_n", and overwrites the existing Area field. Maybe folks should add some safety code like:

ldef = lyr.GetLayerDefn()

if ldef.GetFieldIndex("Area") != -1:

    print "'Area' field already defined"

    ... # exit or overwrite logic

share|improve this answer

edited Mar 4 '13 at 21:23

Dave X

840517

answered Sep 28 '12 at 15:51

R.K.R.K.

15.9k351105

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You're welcome. An upvote would be nice, too ;-)
  
  – R.K.
  Sep 28 '12 at 16:15
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I have similar project in .net,code is similar as well.In your code you mentioned that after SetField method,should use SetFeature in order to update layer.Unfortunately that doesn't work.Any ideas ?
  
  – Myra
  Feb 6 '13 at 6:37
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Myra You might want to ask that on a separate question. Unfortunately, I'm not really familiar with .NET. Hopefully, others can help you. Just post the question :)
  
  – R.K.
  Feb 21 '13 at 15:19
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Great, wonder why "SetFeature" is mentioned nowhere in the docs...
  
  – adamczi
  Jul 11 '18 at 21:00
  

  
  
  
  

add a comment | 

15

You have to use lyr.SetFeature(i) to trigger the update in your shape file.
You'll have to close the data sources in the end so things get written.

import sys

import ogr



ds = ogr.Open( 'tttttttttt.shp', update = 1 )

if ds is None:

    print "Open failed./n"

    sys.exit( 1 )



lyr = ds.GetLayerByName( "tttttttttt" )

lyr.ResetReading()



field_defn = ogr.FieldDefn( "Area", ogr.OFTReal )

lyr.CreateField(field_defn)



for i in lyr:

    # feat = lyr.GetFeature(i) 

    geom = i.GetGeometryRef()

    area = geom.GetArea()

    print 'Area =', area

    lyr.SetFeature(i)

    i.SetField( "Area", area )

    lyr.SetFeature(i)

ds = None

*Low-rep comment and concern: If the 'Area' field already exists, this code creates an extra field, like "Area_n", and overwrites the existing Area field. Maybe folks should add some safety code like:

ldef = lyr.GetLayerDefn()

if ldef.GetFieldIndex("Area") != -1:

    print "'Area' field already defined"

    ... # exit or overwrite logic

share|improve this answer

edited Mar 4 '13 at 21:23

Dave X

840517

answered Sep 28 '12 at 15:51

R.K.R.K.

15.9k351105

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You're welcome. An upvote would be nice, too ;-)
  
  – R.K.
  Sep 28 '12 at 16:15
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I have similar project in .net,code is similar as well.In your code you mentioned that after SetField method,should use SetFeature in order to update layer.Unfortunately that doesn't work.Any ideas ?
  
  – Myra
  Feb 6 '13 at 6:37
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Myra You might want to ask that on a separate question. Unfortunately, I'm not really familiar with .NET. Hopefully, others can help you. Just post the question :)
  
  – R.K.
  Feb 21 '13 at 15:19
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Great, wonder why "SetFeature" is mentioned nowhere in the docs...
  
  – adamczi
  Jul 11 '18 at 21:00
  

  
  
  
  

add a comment | 

You have to use lyr.SetFeature(i) to trigger the update in your shape file.
You'll have to close the data sources in the end so things get written.

import sys

import ogr



ds = ogr.Open( 'tttttttttt.shp', update = 1 )

if ds is None:

    print "Open failed./n"

    sys.exit( 1 )



lyr = ds.GetLayerByName( "tttttttttt" )

lyr.ResetReading()



field_defn = ogr.FieldDefn( "Area", ogr.OFTReal )

lyr.CreateField(field_defn)



for i in lyr:

    # feat = lyr.GetFeature(i) 

    geom = i.GetGeometryRef()

    area = geom.GetArea()

    print 'Area =', area

    lyr.SetFeature(i)

    i.SetField( "Area", area )

    lyr.SetFeature(i)

ds = None

*Low-rep comment and concern: If the 'Area' field already exists, this code creates an extra field, like "Area_n", and overwrites the existing Area field. Maybe folks should add some safety code like:

ldef = lyr.GetLayerDefn()

if ldef.GetFieldIndex("Area") != -1:

    print "'Area' field already defined"

    ... # exit or overwrite logic

share|improve this answer

edited Mar 4 '13 at 21:23

Dave X

840517

answered Sep 28 '12 at 15:51

R.K.R.K.

15.9k351105

import sys

import ogr



ds = ogr.Open( 'tttttttttt.shp', update = 1 )

if ds is None:

    print "Open failed./n"

    sys.exit( 1 )



lyr = ds.GetLayerByName( "tttttttttt" )

lyr.ResetReading()



field_defn = ogr.FieldDefn( "Area", ogr.OFTReal )

lyr.CreateField(field_defn)



for i in lyr:

    # feat = lyr.GetFeature(i) 

    geom = i.GetGeometryRef()

    area = geom.GetArea()

    print 'Area =', area

    lyr.SetFeature(i)

    i.SetField( "Area", area )

    lyr.SetFeature(i)

ds = None

ldef = lyr.GetLayerDefn()

if ldef.GetFieldIndex("Area") != -1:

    print "'Area' field already defined"

    ... # exit or overwrite logic

share|improve this answer

edited Mar 4 '13 at 21:23

Dave X

840517

answered Sep 28 '12 at 15:51

R.K.R.K.

15.9k351105

edited Mar 4 '13 at 21:23

Dave X

840517

edited Mar 4 '13 at 21:23

Dave X

840517

answered Sep 28 '12 at 15:51

R.K.R.K.

15.9k351105

answered Sep 28 '12 at 15:51

R.K.R.K.

15.9k351105