QGIS Union: Could not add feature with geometry type GeometryCollection to layer of type MultiPolygon

Question

I overlay several Shapefile layers with Vector > Geoprocessing Tools > Union in QGIS. The first five layers do work. However, when I'm trying to add another layer I receive the following error during the execution:

QGIS version: 3.16.0-Hannover
QGIS code revision: 43b64b13f3
Qt version: 5.11.2
GDAL version: 3.1.4
GEOS version: 3.8.1-CAPI-1.13.3
PROJ version: Rel. 6.3.2, May 1st, 2020
Processing algorithm…
Algorithm 'Union' starting…
Input parameters:
{ 'INPUT' : 'C:/Users/lucas/Desktop/Master Thesis/Python/Data_New/gis_data.shp', 'OUTPUT' : 'TEMPORARY_OUTPUT', 'OVERLAY' : 'C:/Users/lucas/Desktop/Master Thesis/Python/Data_New/Soil Moisture/Soil_Moisture_FR_CRS.shp', 'OVERLAY_FIELDS_PREFIX' : '' }

Feature (53320) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (54670) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (55047) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (61804) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (62961) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (63483) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (66206) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (66218) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (53320) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature could not be written to Union_146bc6b6_c533_488a_9c56_d9f8c0a8d007: Could not add feature with geometry type GeometryCollection to layer of type MultiPolygon
Feature (54670) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature could not be written to Union_146bc6b6_c533_488a_9c56_d9f8c0a8d007: Could not add feature with geometry type GeometryCollection to layer of type MultiPolygon
Feature (55047) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (61804) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (62961) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (63483) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature could not be written to Union_146bc6b6_c533_488a_9c56_d9f8c0a8d007: Could not add feature with geometry type GeometryCollection to layer of type MultiPolygon
Feature (66206) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (66218) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (53320) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (54670) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (55047) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (61804) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (62961) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (63483) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (66206) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
Feature (66218) from “gis_data” has invalid geometry and has been skipped. Please fix the geometry or change the Processing setting to the “Ignore invalid input features” option.
GEOS geoprocessing error: difference failed.


Execution failed after 2419.39 seconds

Loading resulting layers
Algorithm 'Union' finished

The Shapefile I want to add consists of several processed Rasterfiles from the german weather service (https://opendata.dwd.de/climate_environment/CDC/grids_germany/multi_annual/soil_moist/). The rasterfiles contain soil moisture data of individual months, that I process one single layer.

My main processing steps were:

1. Use Field Calculator with

(("grids_germany_multi_annual_soil_moist_1991-2010_01.asc@1" > 29) AND ("grids_germany_multi_annual_soil_moist_1991-2010_01.asc@1" <= 50)) * 1 +(("grids_germany_multi_annual_soil_moist_1991-2010_01.asc@1" > 50) AND ("grids_germany_multi_annual_soil_moist_1991-2010_01.asc@1" <= 81)) * 2 + (("grids_germany_multi_annual_soil_moist_1991-2010_01.asc@1" > 81) AND ("grids_germany_multi_annual_soil_moist_1991-2010_01.asc@1" <= 110)) * 1 +("grids_germany_multi_annual_soil_moist_1991-2010_01.asc@1" > 110) * 0

to classify soil moisture stages to allow easier data handling and merging

2. Use Raster > Conversion > Polygonize to vectorize the raster data
3. Use Fix Geometries to avoid damaged polygons
4. Use Vector > Geoprocessing Tools > Clip to clip to investgation area boundaries
5. Use Vector > Geoprocessing Tools > Union to join the shapefiles
6. Use Field Calculator with

CASE
WHEN "SM1" = 0 OR "SM6" = 0 OR "SM7" = 0 OR "SM8" = 0 OR "SM9" = 0 OR "SM11" = 0 OR "SM12" = 0 THEN  0
WHEN "SM1" = 2 AND "SM6" = 2 AND "SM7" = 2 AND "SM8" = 2 AND "SM9" = 2 AND "SM11" = 2 AND "SM12" = 2 THEN  0
ELSE 1
END

to create Moisture Category.

7. Delete individual months
8. Save to correct CRS

Then I want to add this processed Shapfile to another one and get the error.

I can't see why the Geometry Type of my Shapefile should be GeometryCollection. Is there a way to change the Geometry Type or another way of combining the Shapefiles?

Answer 1

I have found a solution that worked for me:

1. I used Fix Geometries from the Processing Toolbox to repair invalid/damaged polygons
2. I used Polygon Union from the Processing Toolbox to join the shapefiles without error message