QGIS tool to correct geometries overlapping antimeridian by splitting polygons in order to create multi-polygon.
- "correct" negative x-values of the geometries so it "overflows" the projection's extent, e.g.,
-173will become187 - cut the polygon using a very thin buffer at the longitude
180using the Difference tool which will create a multi-polygon - undo/correct the changes to the geometries (
187becomes-173again) which are overlapping and the multi-polygon has 2 parts on both sides of the map
- Download script file
split_at_antimeridian.py - Make sure Shapely is installed (see section Dependencies)
- Open Processing Toolbox panel (see menu Processing and then Toolbox)
- Click the dropdown in the panel's toolbar with the Python icon
- Select Add Script to Toolbox..., find script file and add it
- You then find the tool at the bottom of the tree under Scripts, Dal Tools and then *Correct geometries overlapping antimeridian *
Tested with QGIS 3.22 on Windows 10
Copyright (c) 2022 Thomas Zuberbuehler / Dalhousie University
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.
THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
This tool requires PyQGIS and Shapely.
- In QGIS, go to Plugins, then Python Console
- Then click on the paper and pen toolbar icon (Show Editor)
- Copy/paste following code into the editor
- Click the green run button in editor's toolbar
import os
import sys
import subprocess
def find_python():
if sys.platform != "win32":
return sys.executable
for path in sys.path:
assumed_path = os.path.join(path, "python.exe")
if os.path.isfile(assumed_path):
return assumed_path
raise Exception("Python executable not found")
python_exe = find_python()
subprocess.check_call([python_exe, "-m", "pip", "install", "shapely"])Note: Installing an additional Python package with QGIS can be tricky. It's always recommended having a backup before doing so.