转海外：APM 多轴3.4Dev固件的“地形跟随”功能演示

Copter-3.4-dev Terrain Following。

First test flight of terrain following using google maps altitude data (i.e. no sonar). Google maps provides it's altitude data in 100m square blocks and we interpolate between them. This means it's quite common for the data to be 10m off in places so we need to consider this when planning a mission (i.e. don't fly too low!)