diff --git a/vendor/clouds3d.js b/vendor/clouds3d.js
index ec2142a..bb76aec 100644
--- a/vendor/clouds3d.js
+++ b/vendor/clouds3d.js
@@ -329,10 +329,11 @@ function drawTileAt(lng, perp, dx, dz, centerTileX, centerTileY) {
     // corridor's long axis (flight direction +Z) appears as a vertical
     // strip on canvas, matching the way depth maps on screen.
     // UNPACK_FLIP_Y_WEBGL=true inverts V: canvas top -> texture V=1 (top).
-    // To put lng=+12 (corridor front in N flight) at screen TOP we put it
-    // at canvas top (small canvasY). Same inversion for perp so world
-    // east (dx>0, perp<0) ends up at canvas right (large canvasX).
-    var canvasX = (-perp + halfPerp + 0.5) * GROUND_TILE_SIZE;
+    // For lng axis (Y): invert canvasY so lng=+12 (corridor front in
+    // N flight) lands at small canvasY (= screen top after flip).
+    // For perp axis (X): keep the natural sign so world east (dx>0)
+    // ends up at canvasX > halfPerp area (right side of canvas).
+    var canvasX = (perp + halfPerp + 0.5) * GROUND_TILE_SIZE;
     var canvasY = (-lng + halfLong + 0.5) * GROUND_TILE_SIZE;
     if (canvasX < 0 || canvasX >= groundCanvas.width || canvasY < 0 || canvasY >= groundCanvas.height) {
         return Promise.resolve(false);