public final Geometry validatedPolygon() throws GeometryException {
    if (!canBePolygon()) {
      throw new GeometryException("feature_not_polygon", "cannot be polygon", true);
    }
    return validPolygon != null ? validPolygon : (validPolygon = computeValidPolygon());
  }
Returns this feature as a valid {@link Polygon} or {@link MultiPolygon} in world web mercator coordinates.
<p>
Validating and fixing invalid polygons can be expensive, so use only if necessary. Invalid polygons will also be
fixed at render-time.

@throws GeometryException if an error occurs constructing the geometry, or of this feature should not be
                          interpreted as a line
planetiler-core/src/main/java/com/onthegomap/planetiler/geo/WithGeometry.java