visualizer: change set_cam_target to expect right-handed coord input

* update docstring of set_cam_target
* fix set_cam_pos behavior
* update demo.ipynb with example on changing cam focus & position

examples/demo.ipynb

@@ -417,7 +417,9 @@
   },
   {
    "cell_type": "markdown",
-   "metadata": {},
+   "metadata": {
+    "tags": []
+   },
    "source": [
     "## Cart-Pole\n",
     "\n",
@@ -453,6 +455,47 @@
     "    time.sleep(0.01)"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Let's set the camera position to above left of the cartpole:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "vis.jupyter_cell()"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "vis.set_cam_pos([0.6, -1.0, 1.0])"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Let's change the focus to the leftmost 'l' character:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "vis.set_cam_target([0.0, -1.0, 0.0])"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,
@@ -477,9 +520,9 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.5.2"
+   "version": "3.9.13"
   }
  },
  "nbformat": 4,
- "nbformat_minor": 2
+ "nbformat_minor": 4
 }

src/meshcat/visualizer.py

@@ -158,15 +158,17 @@ def set_animation(self, animation, play=True, repetitions=1):
         return self.window.send(SetAnimation(animation, play=play, repetitions=repetitions))
 
     def set_cam_target(self, value):
-        """Set camera target."""
-        return self.window.send(SetCamTarget(value))
+        """Set camera target (in right-handed coordinates (x,y,z))."""
+        v = list(value)
+        v[1], v[2] = v[2], -v[1]  # convert to left-handed (x,z,-y)
+        return self.window.send(SetCamTarget(v))
 
     def set_cam_pos(self, value):
         """Set camera position (in right-handed coordinates (x,y,z))."""
         path = "/Cameras/default/rotated/<object>"
         v = list(value)
         v[1], v[2] = v[2], -v[1]  # convert to left-handed (x,z,-y)
-        return self[path].set_property("position", value)
+        return self[path].set_property("position", v)
 
     def get_image(self, w=None, h=None):
         """Save an image"""