Returns a feature containing the union of the geometry of a feature. This leaves single geometries untouched, and unions multi geometries.
|Element||The feature the geometry of which is being unioned.|
|ErrorMargin, default: null||The maximum amount of error tolerated when performing any necessary reprojection.|
|Projection, default: null||If specified, the union will be performed in this projection. Otherwise it will be performed in a spherical coordinate system.|