Google Earth is a great way to estimate the height of nearby obstacles. Here’s the method I use to estimate my RTH altitude to ensure I clear all obstacles in my flight path:

**1)** Find the elevation at the takeoff location. In my example below, the takeoff location is the red circle and the elevation at that point is **110 feet**.

**2)** Scroll around on the map in Google Earth and find the tallest obstacle in the area. In my example below, the tallest obstacle is the top of this building *(the red circle)*. It has an elevation of **597 feet**.

**3)** Calculate the best RTH altitude for this flight. In this case, **487 feet** *(597 feet minus 110 feet)* is the tallest obstacle in the area above the takeoff location. I’d then add at least **50 feet** to that value since I know the IMU is only able to estimate the current altitude *(it’s never 100% accurate)*. That means the RTH altitude for this flight would need to be set to at least **537 feet** *(164 meters)*.