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OGR: Load layer with sql statement and write to new data set

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2

I am having difficulties after loading a shapefile with a sql statement with ogr.
The layer and its features seem to be correctly loaded. Still I am not able to write them into a new shapefile or pass the layer to the gdal_rasterize function.
The shapefile remains an empty file and the raster has the typical no input/something wrong happend values from 1.79..e+308 to -1.79..e+308 (not visualized in QGIS).
Code example for the creation of the shapefile (paths are omitted):

file = ogr.Open(file_path)
sql = 'Select * From where <= 5'.format(layer_name, "CS")
tmp_layer = file.ExecuteSQL(sql)
print(tmp_layer)
>>><osgeo.ogr.Layer; proxy of <Swig Object of type 'OGRLayerShadow *' at 0x00000214D99617E0> >
for feat in tmp_layer:
 print(feat.GetField('CS'))
 >>>(prints the field of the subset of features as expected)
drv = ogr.GetDriverByName("ESRI Shapefile")
out_ds = drv.CreateDataSource(output_folder + '/asd.shp')
proj = tmp_layer.GetSpatialRef()
layer = out_ds.CreateLayer('asd', proj, ogr.wkbMultiPolygon)
# copy the schema of the original shapefile to the destination shapefile
lyr_def = tmp_layer.GetLayerDefn()
for i in range(lyr_def.GetFieldCount()):
 layer.CreateField(lyr_def.GetFieldDefn(i))
#write features from tmp_layer to new layer
for feat in tmp_layer:
 layer.CreateFeature(feat)
out_ds = layer = None

I am not able to find my mistake and would appreciate some help :)

gdal ogr

share|improve this question

asked 8 hours ago

gillagilla

1086

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Does it work without the filtering? Does it work with different data (try naturalearthdata.com since that is free for everyone to use)?
  
  – bugmenot123
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Oh damn... I tried so much and I dont know what wrent wrong before - because I am quite sure I tested it without the iteration over the features. It seems that while iterating over the features these get consumed and are not available anymore... And thats the whole problem! (So it didnt work without the sql statement)
  
  – gilla
  7 hours ago
  

  
  
  
  

add a comment | 

2

I am having difficulties after loading a shapefile with a sql statement with ogr.
The layer and its features seem to be correctly loaded. Still I am not able to write them into a new shapefile or pass the layer to the gdal_rasterize function.
The shapefile remains an empty file and the raster has the typical no input/something wrong happend values from 1.79..e+308 to -1.79..e+308 (not visualized in QGIS).
Code example for the creation of the shapefile (paths are omitted):

file = ogr.Open(file_path)
sql = 'Select * From where <= 5'.format(layer_name, "CS")
tmp_layer = file.ExecuteSQL(sql)
print(tmp_layer)
>>><osgeo.ogr.Layer; proxy of <Swig Object of type 'OGRLayerShadow *' at 0x00000214D99617E0> >
for feat in tmp_layer:
 print(feat.GetField('CS'))
 >>>(prints the field of the subset of features as expected)
drv = ogr.GetDriverByName("ESRI Shapefile")
out_ds = drv.CreateDataSource(output_folder + '/asd.shp')
proj = tmp_layer.GetSpatialRef()
layer = out_ds.CreateLayer('asd', proj, ogr.wkbMultiPolygon)
# copy the schema of the original shapefile to the destination shapefile
lyr_def = tmp_layer.GetLayerDefn()
for i in range(lyr_def.GetFieldCount()):
 layer.CreateField(lyr_def.GetFieldDefn(i))
#write features from tmp_layer to new layer
for feat in tmp_layer:
 layer.CreateFeature(feat)
out_ds = layer = None

I am not able to find my mistake and would appreciate some help :)

gdal ogr

share|improve this question

asked 8 hours ago

gillagilla

1086

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Does it work without the filtering? Does it work with different data (try naturalearthdata.com since that is free for everyone to use)?
  
  – bugmenot123
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Oh damn... I tried so much and I dont know what wrent wrong before - because I am quite sure I tested it without the iteration over the features. It seems that while iterating over the features these get consumed and are not available anymore... And thats the whole problem! (So it didnt work without the sql statement)
  
  – gilla
  7 hours ago
  

  
  
  
  

add a comment | 

I am having difficulties after loading a shapefile with a sql statement with ogr.
The layer and its features seem to be correctly loaded. Still I am not able to write them into a new shapefile or pass the layer to the gdal_rasterize function.
The shapefile remains an empty file and the raster has the typical no input/something wrong happend values from 1.79..e+308 to -1.79..e+308 (not visualized in QGIS).
Code example for the creation of the shapefile (paths are omitted):

file = ogr.Open(file_path)
sql = 'Select * From where <= 5'.format(layer_name, "CS")
tmp_layer = file.ExecuteSQL(sql)
print(tmp_layer)
>>><osgeo.ogr.Layer; proxy of <Swig Object of type 'OGRLayerShadow *' at 0x00000214D99617E0> >
for feat in tmp_layer:
 print(feat.GetField('CS'))
 >>>(prints the field of the subset of features as expected)
drv = ogr.GetDriverByName("ESRI Shapefile")
out_ds = drv.CreateDataSource(output_folder + '/asd.shp')
proj = tmp_layer.GetSpatialRef()
layer = out_ds.CreateLayer('asd', proj, ogr.wkbMultiPolygon)
# copy the schema of the original shapefile to the destination shapefile
lyr_def = tmp_layer.GetLayerDefn()
for i in range(lyr_def.GetFieldCount()):
 layer.CreateField(lyr_def.GetFieldDefn(i))
#write features from tmp_layer to new layer
for feat in tmp_layer:
 layer.CreateFeature(feat)
out_ds = layer = None

I am not able to find my mistake and would appreciate some help :)

gdal ogr

share|improve this question

asked 8 hours ago

gillagilla

1086

file = ogr.Open(file_path)
sql = 'Select * From where <= 5'.format(layer_name, "CS")
tmp_layer = file.ExecuteSQL(sql)
print(tmp_layer)
>>><osgeo.ogr.Layer; proxy of <Swig Object of type 'OGRLayerShadow *' at 0x00000214D99617E0> >
for feat in tmp_layer:
 print(feat.GetField('CS'))
 >>>(prints the field of the subset of features as expected)
drv = ogr.GetDriverByName("ESRI Shapefile")
out_ds = drv.CreateDataSource(output_folder + '/asd.shp')
proj = tmp_layer.GetSpatialRef()
layer = out_ds.CreateLayer('asd', proj, ogr.wkbMultiPolygon)
# copy the schema of the original shapefile to the destination shapefile
lyr_def = tmp_layer.GetLayerDefn()
for i in range(lyr_def.GetFieldCount()):
 layer.CreateField(lyr_def.GetFieldDefn(i))
#write features from tmp_layer to new layer
for feat in tmp_layer:
 layer.CreateFeature(feat)
out_ds = layer = None

share|improve this question

asked 8 hours ago

gillagilla

1086

share|improve this question

asked 8 hours ago

gillagilla

1086

asked 8 hours ago

gillagilla

1086

asked 8 hours ago

gillagilla

1086

2 Answers
2

active

oldest

votes

2

When you iterate over the layer it essentially calls lyr.GetNextFeature(). After the last feature the pointer remains at the end which is why when you iterate over the layer the second time it doesn't find any features.

If you plan on iterating over the layer more than once you need to make sure you call lyr.ResetReading() to reset the pointer to the first feature.

#write features from tmp_layer to new layer
tmp_layer.ResetReading()
for feat in tmp_layer:
 layer.CreateFeature(feat)

share|improve this answer

answered 3 hours ago

AliAli

3,1341822

add a comment | 

1

The iteration over the features seem to consume these features like in an interator. Thus omitting the iteration for printing will solve the problem.

share|improve this answer

edited 3 hours ago

Marcelo Villa

1,4971818

answered 7 hours ago

gillagilla

1086

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You can accept your answer so future readers know what the solution is.
  
  – Marcelo Villa
  4 hours ago
  

  
  
  
  

add a comment | 

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2

When you iterate over the layer it essentially calls lyr.GetNextFeature(). After the last feature the pointer remains at the end which is why when you iterate over the layer the second time it doesn't find any features.

If you plan on iterating over the layer more than once you need to make sure you call lyr.ResetReading() to reset the pointer to the first feature.

#write features from tmp_layer to new layer
tmp_layer.ResetReading()
for feat in tmp_layer:
 layer.CreateFeature(feat)

share|improve this answer

answered 3 hours ago

AliAli

3,1341822

add a comment | 

2

When you iterate over the layer it essentially calls lyr.GetNextFeature(). After the last feature the pointer remains at the end which is why when you iterate over the layer the second time it doesn't find any features.

If you plan on iterating over the layer more than once you need to make sure you call lyr.ResetReading() to reset the pointer to the first feature.

#write features from tmp_layer to new layer
tmp_layer.ResetReading()
for feat in tmp_layer:
 layer.CreateFeature(feat)

share|improve this answer

answered 3 hours ago

AliAli

3,1341822

add a comment | 

When you iterate over the layer it essentially calls lyr.GetNextFeature(). After the last feature the pointer remains at the end which is why when you iterate over the layer the second time it doesn't find any features.

If you plan on iterating over the layer more than once you need to make sure you call lyr.ResetReading() to reset the pointer to the first feature.

#write features from tmp_layer to new layer
tmp_layer.ResetReading()
for feat in tmp_layer:
 layer.CreateFeature(feat)

share|improve this answer

answered 3 hours ago

AliAli

3,1341822

#write features from tmp_layer to new layer
tmp_layer.ResetReading()
for feat in tmp_layer:
 layer.CreateFeature(feat)

share|improve this answer

answered 3 hours ago

AliAli

3,1341822

answered 3 hours ago

AliAli

3,1341822

answered 3 hours ago

AliAli

3,1341822

1

The iteration over the features seem to consume these features like in an interator. Thus omitting the iteration for printing will solve the problem.

share|improve this answer

edited 3 hours ago

Marcelo Villa

1,4971818

answered 7 hours ago

gillagilla

1086

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You can accept your answer so future readers know what the solution is.
  
  – Marcelo Villa
  4 hours ago
  

  
  
  
  

add a comment | 

1

The iteration over the features seem to consume these features like in an interator. Thus omitting the iteration for printing will solve the problem.

share|improve this answer

edited 3 hours ago

Marcelo Villa

1,4971818

answered 7 hours ago

gillagilla

1086

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You can accept your answer so future readers know what the solution is.
  
  – Marcelo Villa
  4 hours ago
  

  
  
  
  

add a comment | 

The iteration over the features seem to consume these features like in an interator. Thus omitting the iteration for printing will solve the problem.

share|improve this answer

edited 3 hours ago

Marcelo Villa

1,4971818

answered 7 hours ago

gillagilla

1086

share|improve this answer

edited 3 hours ago

Marcelo Villa

1,4971818

answered 7 hours ago

gillagilla

1086

edited 3 hours ago

Marcelo Villa

1,4971818

edited 3 hours ago

Marcelo Villa

1,4971818

answered 7 hours ago

gillagilla

1086

answered 7 hours ago

gillagilla

1086