Switch to ESRI World_Street_Map via local CORS proxy

Carto Voyager was returning 'API Key required' content for the
user (likely rate-limited or IP-blocked by Carto). Switched to
ESRI World_Street_Map which has CORS-friendly tiles with plenty
of place names and street labels.

URL format is different from Carto: {z}/{y}/{x}.jpg (y before x,
jpg not png). Updated the build to match. The local /esri/
proxy in default.conf handles the upstream CORS-incompatibility
by adding permissive CORS headers and a proper User-Agent.

default.conf

@@ -8,10 +8,8 @@ server {
         try_files $uri $uri/ =404;
     }
 
-    # CORS proxy for map tiles. Forwards to the upstream tile server
+    # CORS proxy for Carto basemaps (place names, OSM-derived).
-    # but injects permissive CORS headers so the browser can load
+    # URL format: /carto/voyager/{z}/{x}/{y}.png
-    # tiles via cross-origin img.src requests. The 'resolver' is
-    # required by the proxy module to resolve the upstream hostname.
     location ^~ /carto/ {
         resolver 1.1.1.1 8.8.8.8 ipv6=off valid=300s;
         proxy_pass https://a.basemaps.cartocdn.com/;
@@ -23,6 +21,22 @@ server {
         add_header Access-Control-Max-Age 86400 always;
     }
 
+    # CORS proxy for ESRI World_Street_Map. URL format:
+    # /esri/wsm/{z}/{y}/{x}.jpg -> ESRI /ArcGIS/.../World_Street_Map/.../tile/{z}/{y}/{x}
+    location ^~ /esri/ {
+        resolver 1.1.1.1 8.8.8.8 ipv6=off valid=300s;
+        rewrite ^/esri/streets/(.*)$ /ArcGIS/rest/services/World_Street_Map/MapServer/tile/$1 break;
+        rewrite ^/esri/topo/(.*)$ /ArcGIS/rest/services/World_Topo_Map/MapServer/tile/$1 break;
+        rewrite ^/esri/imagery/(.*)$ /ArcGIS/rest/services/World_Imagery/MapServer/tile/$1 break;
+        proxy_pass https://server.arcgisonline.com;
+        proxy_ssl_server_name on;
+        proxy_set_header Host server.arcgisonline.com;
+        proxy_set_header User-Agent "Mozilla/5.0 (compatible; tile-proxy)";
+        add_header Access-Control-Allow-Origin "*" always;
+        add_header Access-Control-Allow-Methods "GET, HEAD, OPTIONS" always;
+        add_header Access-Control-Max-Age 86400 always;
+    }
+
     # CORS preflight handler
     location ~* \.(png|jpg)$ {
         if ($request_method = 'OPTIONS') {

vendor/clouds3d.js

@@ -284,7 +284,7 @@ function init(canvas) {
 // mosaic centre always corresponds to UV (0.5, 0.5).
 // Tile source: Carto basemaps Voyager style (with place names).
 // Free, CORS-enabled, OSM-derived. URL format {z}/{x}/{y}.png.
-var GROUND_TILE_URL = '/carto/voyager/';
+var GROUND_TILE_URL = '/esri/streets/';
 var GROUND_TILE_Z = 11;
 var GROUND_TILE_SIZE = 256;
 // Fetch direction: which way the tile corridor is oriented.
@@ -318,8 +318,9 @@ function fetchTileImage(tileX, tileY) {
         img.crossOrigin = 'anonymous';
         img.onload = function() { resolve(img); };
         img.onerror = function() { reject(new Error('tile fetch failed')); };
-        // Carto/OSM-style format: {z}/{x}/{y}.png via local proxy
+        // ESRI World_Street_Map format: {z}/{y}/{x}.jpg via local
-        img.src = GROUND_TILE_URL + GROUND_TILE_Z + '/' + tileX + '/' + tileY + '.png';
+        // proxy. (y before x, jpg not png)
+        img.src = GROUND_TILE_URL + GROUND_TILE_Z + '/' + tileY + '/' + tileX + '.jpg';
     });
 }