Change how non-driveable roads (cycleways) work in the LTN tool and

blockfinding. Stop using them as parts of block boundaries, and stop
drawing special "car-free" cells around them.

Motivation in the PR description.

apps/ltn/src/colors.rs

@@ -30,7 +30,6 @@ lazy_static::lazy_static! {
     pub static ref PLAN_ROUTE_WALK: Color = Color::BLUE;
 }
 
-pub const CAR_FREE_CELL: Color = Color::GREEN.alpha(0.5);
 pub const DISCONNECTED_CELL: Color = Color::RED.alpha(0.5);
 
 pub const OUTLINE: Color = Color::BLACK;

apps/ltn/src/draw_cells.rs

@@ -138,11 +138,9 @@ impl RenderCellsBuilder {
         let adjacencies = diffusion(&mut grid, boundary_marker);
         let mut cell_colors = color_cells(neighborhood.cells.len(), adjacencies);
 
-        // Color car-free cells in a special way
+        // Color some special cells
         for (idx, cell) in neighborhood.cells.iter().enumerate() {
-            if cell.car_free {
+            if cell.is_disconnected() {
-                cell_colors[idx] = colors::CAR_FREE_CELL;
-            } else if cell.is_disconnected() {
                 cell_colors[idx] = colors::DISCONNECTED_CELL;
             }
         }

apps/ltn/src/neighborhood.rs

@@ -34,15 +34,12 @@ pub struct Cell {
     pub roads: BTreeMap<RoadID, DistanceInterval>,
     /// Intersections where this cell touches the boundary of the neighborhood.
     pub borders: BTreeSet<IntersectionID>,
-    /// This cell only contains roads that ban cars.
-    pub car_free: bool,
 }
 
 impl Cell {
-    /// A cell is disconnected if it's not connected to a perimeter road. (The exception is cells
+    /// A cell is disconnected if it's not connected to a perimeter road.
-    /// containing roads that by their OSM classification already ban cars.)
     pub fn is_disconnected(&self) -> bool {
-        self.borders.is_empty() && !self.car_free
+        self.borders.is_empty()
     }
 }
 
@@ -141,14 +138,13 @@ fn find_cells(
     let mut cells = Vec::new();
     let mut visited = BTreeSet::new();
 
-    let mut no_car_roads = Vec::new();
     for start in &perimeter.interior {
         if visited.contains(start) || modal_filters.roads.contains_key(start) {
             continue;
         }
         let start = *start;
+        // Just skip entirely; they're invisible for the purpose of dividing into cells
         if !PathConstraints::Car.can_use_road(map.get_r(start), map) {
-            no_car_roads.push(start);
             continue;
         }
         let cell = floodfill(map, start, borders, &modal_filters);
@@ -163,7 +159,6 @@ fn find_cells(
             let mut cell = Cell {
                 roads: BTreeMap::new(),
                 borders: btreeset! { road.src_i },
-                car_free: false,
             };
             cell.roads.insert(
                 road.id,
@@ -178,7 +173,6 @@ fn find_cells(
             let mut cell = Cell {
                 roads: BTreeMap::new(),
                 borders: btreeset! { road.dst_i },
-                car_free: false,
             };
             cell.roads.insert(
                 road.id,
@@ -191,34 +185,6 @@ fn find_cells(
         }
     }
 
-    // Roads already banning cars should still contribute a cell, so the cell coloring can still
-    // account for them
-    //
-    // TODO Should we attempt to merge adjacent cells like this? If we have lots of tiny pieces of
-    // bike-only roads, they'll each get their own cell
-    for r in no_car_roads {
-        let mut cell = Cell {
-            roads: BTreeMap::new(),
-            borders: BTreeSet::new(),
-            car_free: true,
-        };
-        let road = map.get_r(r);
-        if borders.contains(&road.src_i) {
-            cell.borders.insert(road.src_i);
-        }
-        if borders.contains(&road.dst_i) {
-            cell.borders.insert(road.dst_i);
-        }
-        cell.roads.insert(
-            road.id,
-            DistanceInterval {
-                start: Distance::ZERO,
-                end: road.length(),
-            },
-        );
-        cells.push(cell);
-    }
-
     cells
 }
 
@@ -310,6 +276,5 @@ fn floodfill(
     Cell {
         roads: visited_roads,
         borders: cell_borders,
-        car_free: false,
     }
 }

map_model/src/objects/block.rs

@@ -7,7 +7,9 @@ use serde::{Deserialize, Serialize};
 use abstutil::wraparound_get;
 use geom::{Polygon, Pt2D, Ring};
 
-use crate::{CommonEndpoint, Direction, LaneID, Map, RoadID, RoadSideID, SideOfRoad};
+use crate::{
+    CommonEndpoint, Direction, LaneID, Map, PathConstraints, RoadID, RoadSideID, SideOfRoad,
+};
 
 /// A block is defined by a perimeter that traces along the sides of roads. Inside the perimeter,
 /// the block may contain buildings and interior roads. In the simple case, a block represents a
@@ -120,15 +122,16 @@ impl Perimeter {
         perimeters
     }
 
-    /// Trying to form blocks near railways or cycleways that involve bridges/tunnels often causes
+    /// Blockfinding is specialized for the LTN tool, so non-driveable roads (cycleways and light
-    /// overlapping geometry or blocks that're way too large. These are extremely imperfect
+    /// rail) are considered invisible and can't be on a perimeter. Previously, there were also
-    /// heuristics to avoid the worst problems.
+    /// some heuristics here to try to skip certain bridges/tunnels that break the planarity of
+    /// blocks.
     pub fn find_roads_to_skip_tracing(map: &Map) -> HashSet<RoadID> {
         let mut skip = HashSet::new();
         for r in map.all_roads() {
             if r.is_light_rail() {
                 skip.insert(r.id);
-            } else if r.is_cycleway() && r.zorder != 0 {
+            } else if !PathConstraints::Car.can_use_road(r, map) {
                 skip.insert(r.id);
             }
         }

tests/goldenfiles/blockfinding.txt

@@ -1,22 +1,22 @@
 data/system/us/seattle/maps/montlake.bin
-    177 single blocks (0 failures to blockify), 1 partial merges, 0 failures to blockify partitions
+    160 single blocks (0 failures to blockify), 0 partial merges, 0 failures to blockify partitions
 data/system/us/seattle/maps/downtown.bin
-    1526 single blocks (0 failures to blockify), 10 partial merges, 0 failures to blockify partitions
+    1309 single blocks (0 failures to blockify), 1 partial merges, 0 failures to blockify partitions
 data/system/us/seattle/maps/lakeslice.bin
-    1063 single blocks (0 failures to blockify), 1 partial merges, 0 failures to blockify partitions
+    1009 single blocks (0 failures to blockify), 1 partial merges, 0 failures to blockify partitions
 data/system/us/phoenix/maps/tempe.bin
-    425 single blocks (1 failures to blockify), 0 partial merges, 0 failures to blockify partitions
+    419 single blocks (1 failures to blockify), 0 partial merges, 0 failures to blockify partitions
 data/system/gb/bristol/maps/east.bin
-    1059 single blocks (3 failures to blockify), 6 partial merges, 0 failures to blockify partitions
+    822 single blocks (3 failures to blockify), 2 partial merges, 0 failures to blockify partitions
 data/system/gb/leeds/maps/north.bin
-    2597 single blocks (5 failures to blockify), 17 partial merges, 1 failures to blockify partitions
+    1936 single blocks (1 failures to blockify), 6 partial merges, 1 failures to blockify partitions
 data/system/gb/london/maps/camden.bin
-    1565 single blocks (1 failures to blockify), 5 partial merges, 0 failures to blockify partitions
+    1046 single blocks (2 failures to blockify), 3 partial merges, 0 failures to blockify partitions
 data/system/gb/london/maps/southwark.bin
-    2195 single blocks (3 failures to blockify), 11 partial merges, 1 failures to blockify partitions
+    1326 single blocks (1 failures to blockify), 5 partial merges, 1 failures to blockify partitions
 data/system/gb/manchester/maps/levenshulme.bin
-    1353 single blocks (1 failures to blockify), 0 partial merges, 0 failures to blockify partitions
+    1244 single blocks (1 failures to blockify), 0 partial merges, 0 failures to blockify partitions
 data/system/fr/lyon/maps/center.bin
-    5216 single blocks (5 failures to blockify), 26 partial merges, 1 failures to blockify partitions
+    3818 single blocks (3 failures to blockify), 12 partial merges, 0 failures to blockify partitions
 data/system/us/seattle/maps/north_seattle.bin
-    3418 single blocks (1 failures to blockify), 6 partial merges, 1 failures to blockify partitions
+    3286 single blocks (1 failures to blockify), 7 partial merges, 0 failures to blockify partitions