osm edits

README.md

@@ -96,11 +96,47 @@ Range assets (start / mid / end) translate as a rigid body — all three vertice
 
 ## OSM road editing
 
+### Modes
 - **OSM tools…** modal — generate roads for the visible bbox (Overpass), import existing GeoJSON, export current roads, prune small road classes.
-- **OSM edit mode** — drag any road's vertex to refine the centerline. Markers are gated by zoom ≥ 14 and capped at 80 vertices / 40 ghost dots per viewport so the map stays responsive.
-- **Flip road direction** — cycle a road's `oneway` between 0 / 1 / -1 when it's wrong.
+- **Edit OSM roads** button — toggles OSM edit mode. While on, every other layer is dimmed and only OSM roads are interactive.
 - **Lane offset (m)** — controls the parallel offset used by snap-to-road. Range 0.1–30 m.
 
+### Picking a road to edit
+1. Turn on **Edit OSM roads** (right panel → Data section).
+2. Zoom in to **z ≥ 14** — vertex handles only render at that zoom or deeper, to keep the map responsive.
+3. Click any road. Its yellow `•` vertex pins appear; other roads stay un-pinned. The selected road's id is shown in the OSM-edit panel.
+
+### Modifying a road
+- **Drag a yellow `•` pin** — moves that vertex to wherever you drop it. The change is saved immediately.
+- **Click a yellow `+` ghost pin** between two vertices — inserts a new vertex at that midpoint. Useful when an OSM segment is too sparse for the curve.
+- **Flip direction** — cycles `oneway` through forward (`1`) → reverse (`-1`) → undirected (`0`). Use when OSM has the heading wrong on a divided road.
+
+### Deleting vertices
+Two tools, depending on scope:
+
+**A. Surgical — Shift-click + Del**
+1. Hold **Shift** and click a vertex pin → it turns red with an `✕`.
+2. Repeat to mark more.
+3. Press **Del** (or Backspace) → all marked vertices are removed in one shot.
+4. The "Currently marked: N" label in the panel shows how many you've flagged. **Clear marks** unselects without deleting.
+5. Shift-click a marked vertex again to unmark it individually.
+6. The road must keep ≥ 2 vertices; the backend rejects deletes that would break that.
+
+**B. Sweeping — Simplify by tolerance**
+1. Use the **Simplify (m)** slider in the panel (0.5–20 m, default 2 m). Higher = more aggressive.
+2. Click **Simplify this road**. Runs Douglas-Peucker on the polyline: any vertex within tolerance of the simplified line is dropped.
+3. Status bar reports `before → after` vertex counts.
+4. Try 1–2 m for cleanup, 5+ m for heavy decimation. Re-running with the same tolerance is idempotent.
+
+### Deleting / flipping the whole road
+- **Delete this road** — removes the road outright (with confirmation).
+- **Deselect road** — exits the per-road editing tool but keeps OSM edit mode on.
+
+### Notes
+- OSM road edits are **not** undoable via the Recent actions panel — they're treated like reference-data tweaks. Be deliberate, especially with delete and simplify.
+- Dragging a vertex triggers a single `update_osm_road` write per drag. Bulk delete and simplify are also single writes.
+- After a vertex change, the road line refreshes in real time but the surrounding draggable pins re-render — slight visual flicker is normal.
+
 ---
 
 ## Snap-to-road