From bdb5e99e2b3db51518a9122fc17ea56b009cdb71 Mon Sep 17 00:00:00 2001
From: Dustin Carlino <dabreegster@gmail.com>
Date: Tue, 16 Jul 2024 11:19:20 +0100
Subject: [PATCH] Allow multipolygons as clipping boundaries when converting
 from OSM

---
 CHANGES.md                      |  2 ++
 osm-to-route-snapper/src/lib.rs | 27 ++++++++++++++++++++-------
 user_guide.md                   |  5 +++--
 3 files changed, 25 insertions(+), 9 deletions(-)

diff --git a/CHANGES.md b/CHANGES.md
index 3f0ee28..3253cd1 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -7,6 +7,8 @@ changes.
 
 ## Unreleased
 
+- The OSM importer can now handle MultiPolygon boundaries for clipping
+
 ## 0.4.1
 
 - Removed `fetchWithProgress`, which is a general-purpose utility method that
diff --git a/osm-to-route-snapper/src/lib.rs b/osm-to-route-snapper/src/lib.rs
index db31da3..baf0693 100644
--- a/osm-to-route-snapper/src/lib.rs
+++ b/osm-to-route-snapper/src/lib.rs
@@ -2,7 +2,8 @@ use std::collections::HashMap;
 
 use anyhow::Result;
 use geo::{
-    BooleanOps, Contains, Coord, HaversineLength, Intersects, LineString, MultiLineString, Polygon,
+    BooleanOps, Contains, Coord, HaversineLength, Intersects, LineString, MultiLineString,
+    MultiPolygon,
 };
 use log::{debug, info};
 use osm_reader::{Element, WayID};
@@ -10,7 +11,7 @@ use osm_reader::{Element, WayID};
 use route_snapper_graph::{Edge, NodeID, RouteSnapperMap};
 
 /// Convert input OSM PBF or XML data into a RouteSnapperMap, extracting all highway center-lines.
-/// If a boundary polygon is specified, clips roads to this boundary.
+/// If a boundary polygon or multipolygon is specified, clips roads to this boundary.
 pub fn convert_osm(
     input_bytes: Vec<u8>,
     boundary_gj: Option<String>,
@@ -27,7 +28,14 @@ pub fn convert_osm(
     let mut boundary = None;
     if let Some(gj_string) = boundary_gj {
         let gj: geojson::Feature = gj_string.parse()?;
-        let boundary_geo: Polygon = gj.try_into()?;
+        let boundary_geo: MultiPolygon = if matches!(
+            gj.geometry.as_ref().unwrap().value,
+            geojson::Value::Polygon(_)
+        ) {
+            MultiPolygon(vec![gj.try_into()?])
+        } else {
+            gj.try_into()?
+        };
         boundary = Some(boundary_geo);
     }
 
@@ -83,7 +91,7 @@ fn scrape_elements(
 fn split_edges(
     nodes: HashMap<osm_reader::NodeID, Coord>,
     ways: HashMap<WayID, Way>,
-    boundary: Option<&Polygon>,
+    boundary: Option<&MultiPolygon>,
 ) -> RouteSnapperMap {
     let mut map = RouteSnapperMap {
         nodes: Vec::new(),
@@ -118,7 +126,9 @@ fn split_edges(
                 let mut add_road = true;
                 if let Some(boundary) = boundary {
                     // If this road doesn't intersect the boundary at all, skip it
-                    if !boundary.contains(&geometry) && !boundary.exterior().intersects(&geometry) {
+                    if !boundary.contains(&geometry)
+                        && !boundary.iter().any(|p| p.exterior().intersects(&geometry))
+                    {
                         add_road = false;
                     }
                 }
@@ -161,11 +171,14 @@ fn split_edges(
     map
 }
 
-fn clip(map: &mut RouteSnapperMap, boundary: Polygon) {
+fn clip(map: &mut RouteSnapperMap, boundary: MultiPolygon) {
     // Fix edges crossing the boundary. Edges totally outside the boundary are skipped earlier
     // during split_edges.
     for edge in &mut map.edges {
-        if boundary.exterior().intersects(&edge.geometry) {
+        if boundary
+            .iter()
+            .any(|p| p.exterior().intersects(&edge.geometry))
+        {
             let invert = false;
             let mut multi_line_string =
                 boundary.clip(&MultiLineString::from(edge.geometry.clone()), invert);
diff --git a/user_guide.md b/user_guide.md
index 4f04500..7e00508 100644
--- a/user_guide.md
+++ b/user_guide.md
@@ -13,8 +13,9 @@ file from OpenStreetMap data. The easiest way to do this for smaller areas is
 [in your web browser](https://dabreegster.github.io/route_snapper/import.html).
 
 For larger areas, you need an `.osm.xml` or `.osm.pbf` file, and optionally a
-GeoJSON file with one polygon representing the boundary of your area. You'll
-need to [install Rust](https://www.rust-lang.org/tools/install) to run this:
+GeoJSON file with one polygon or multipolygon representing the boundary of your
+area. You'll need to [install Rust](https://www.rust-lang.org/tools/install) to
+run this:
 
 ```
 cd osm-to-route-snapper