Only send visible map scores based on viewport bounds

The JS hook sends map bounds on load and on pan/zoom. The server
queries only scores within those bounds, dramatically reducing the
payload for band switches and map updates. At zoom 7 (DFW area)
this sends ~2k scores instead of ~95k.

assets/js/propagation_map_hook.js

@@ -23,13 +23,14 @@ export const PropagationMap = {
       { min: 0,  r: 255, g: 79,  b: 79 }    // NEGLIGIBLE - red
     ]
 
-    const initialScores = JSON.parse(this.el.dataset.scores || "[]")
-    this.renderScores(initialScores)
-
     this.handleEvent("update_scores", ({ scores }) => {
       this.renderScores(scores)
     })
 
+    // Send bounds to server on load and on pan/zoom
+    this.sendBounds()
+    this.map.on("moveend", () => this.sendBounds())
+
     // Legend
     const legend = L.control({ position: "bottomright" })
     legend.onAdd = () => {
@@ -166,6 +167,16 @@ export const PropagationMap = {
     return { r: last.r, g: last.g, b: last.b }
   },
 
+  sendBounds() {
+    const b = this.map.getBounds()
+    this.pushEvent("map_bounds", {
+      south: b.getSouth(),
+      north: b.getNorth(),
+      west: b.getWest(),
+      east: b.getEast()
+    })
+  },
+
   destroyed() {
     if (this.map) this.map.remove()
   }

lib/microwaveprop/propagation.ex

@@ -88,8 +88,8 @@ defmodule Microwaveprop.Propagation do
     {:ok, total}
   end
 
-  @doc "Get the latest scores for a band."
-  def latest_scores(band_mhz) do
+  @doc "Get the latest scores for a band, optionally within a bounding box."
+  def latest_scores(band_mhz, bounds \\ nil) do
     latest_time_query =
       from(gs in GridScore,
         where: gs.band_mhz == ^band_mhz,
@@ -101,15 +101,23 @@ defmodule Microwaveprop.Propagation do
         []
 
       latest_time ->
-        Repo.all(
-          from(gs in GridScore,
-            where: gs.band_mhz == ^band_mhz and gs.valid_time == ^latest_time,
-            select: %{lat: gs.lat, lon: gs.lon, score: gs.score}
-          )
+        from(gs in GridScore,
+          where: gs.band_mhz == ^band_mhz and gs.valid_time == ^latest_time,
+          select: %{lat: gs.lat, lon: gs.lon, score: gs.score}
         )
+        |> maybe_filter_bounds(bounds)
+        |> Repo.all()
     end
   end
 
+  defp maybe_filter_bounds(query, nil), do: query
+
+  defp maybe_filter_bounds(query, %{"south" => s, "north" => n, "west" => w, "east" => e}) do
+    from(gs in query,
+      where: gs.lat >= ^s and gs.lat <= ^n and gs.lon >= ^w and gs.lon <= ^e
+    )
+  end
+
   @doc "Get the latest valid_time across all scores."
   def latest_valid_time do
     Repo.one(from(gs in GridScore, select: max(gs.valid_time)))

lib/microwaveprop_web/live/map_live.ex

@@ -10,7 +10,6 @@ defmodule MicrowavepropWeb.MapLive do
   @impl true
   def mount(_params, _session, socket) do
     bands = BandConfig.all_bands()
-    scores = Propagation.latest_scores(@default_band)
     valid_time = Propagation.latest_valid_time()
 
     if connected?(socket) do
@@ -22,15 +21,16 @@ defmodule MicrowavepropWeb.MapLive do
        page_title: "Propagation Map",
        bands: bands,
        selected_band: @default_band,
-       scores: scores,
-       valid_time: valid_time
+       scores: [],
+       valid_time: valid_time,
+       bounds: nil
      )}
   end
 
   @impl true
   def handle_event("select_band", %{"value" => band_str}, socket) do
     band = String.to_integer(band_str)
-    scores = Propagation.latest_scores(band)
+    scores = Propagation.latest_scores(band, socket.assigns.bounds)
 
     socket =
       socket
@@ -41,9 +41,21 @@ defmodule MicrowavepropWeb.MapLive do
     {:noreply, socket}
   end
 
+  def handle_event("map_bounds", bounds, socket) do
+    scores = Propagation.latest_scores(socket.assigns.selected_band, bounds)
+
+    socket =
+      socket
+      |> assign(:bounds, bounds)
+      |> assign(:scores, scores)
+      |> push_event("update_scores", %{scores: scores})
+
+    {:noreply, socket}
+  end
+
   @impl true
   def handle_info({:propagation_updated, valid_time}, socket) do
-    scores = Propagation.latest_scores(socket.assigns.selected_band)
+    scores = Propagation.latest_scores(socket.assigns.selected_band, socket.assigns.bounds)
 
     socket =
       socket
@@ -70,7 +82,7 @@ defmodule MicrowavepropWeb.MapLive do
         id="propagation-map"
         phx-hook="PropagationMap"
         phx-update="ignore"
-        data-scores={Jason.encode!(@scores)}
+        data-scores="[]"
         class="absolute inset-0 z-0"
       >
       </div>