add fov example

Author: powei-lin

data/fov_tum_mono.json

@@ -0,0 +1,11 @@
+{
+  "FovCamera": {
+    "fx": 446.91584,
+    "fy": 447.071232,
+    "cx": 631.2192,
+    "cy": 510.997504,
+    "w": 0.933271000000000,
+    "width": 1280,
+    "height": 1024
+  }
+}