5

I wanted to geopandas.overlay() on lines and polygons : get the geometries from the lines that are not in the polygons.

I tried using geopandas for this :

result = gpd.overlay(my_lines, my_polygons, how='difference')

but I get this error :

TypeError: overlay only takes GeoDataFrames with (multi)polygon geometries

since the overlay method only supports polygons, I did the difference using pyqgis. However I want to know if there is a way to bypass this typeError using geopandas and shapely ?

  • 1
    You can use a buffer around my_lines (to have polygons). Then run result = gpd.overlay(my_buffered_lines, my_polygons, how='difference') You will have the difference between the buffered lines and the polygons. After that, you can use an intersection between my_lines and my_buffered_lines, this will give you the Linestrings you need – Hamri Said Jul 11 '17 at 13:22
3

Meanwhile here is the solution I wrote using pyqgis, it works for me :

my_lines = QgsVectorLayer('/path/to/my_lines.shp', 'my_lines', 'ogr')
my_polygons = QgsVectorLayer('/path/to/my_polygons.shp', 'my_polygons', 'ogr')

diff = processing.runalg("qgis:difference", my_lines, my_polygons, False, None)
result = processing.getObject(diff['OUTPUT'])
_writer = QgsVectorFileWriter.writeAsVectorFormat(result,"/path/to/result.shp","utf-8",None,"ESRI Shapefile")

my_lines_diff_my_polygons = gpd.read_file('/path/to/result.shp')

for this to work, one has to import processing:

import processing
  • Hello, I am trying to use your solution, but the resultant shape file seems to have an empty geometry field, so there's no useful data in it. Have you run into this issue? – Kiran K. Jan 12 '18 at 13:35
  • @KiranK. make sure both your vector layers have the same projection, then if the problem persists close qgis if opened and delete the result file then launch the processing again – Hicham Zouarhi Jan 12 '18 at 13:59
  • 1
    Thank you, I posted too quickly, this time, I made sure both were in the same CRS and it does work. Best Regards, and thanks again! – Kiran K. Jan 12 '18 at 14:08

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