Determining the "optimal" speed, altitude, and overlap you should fly is based on how accurate and how dense you need your data, as well as what types of objects you are trying to capture.
Altitude and Speed
Flying at about 50m (164 ft) AGL and 5-6 m/s (11.2-13.4 mph) is the optimal speed and altitude for getting sub 5 cm (1.97 in) vertical accuracy.
The higher and faster you fly, the less accurate the readings of the sensor will be. However, there are more factors at play than just height and speed.
The reflectivity of the surface you are scanning also plays an important factor. Some surfaces have a harder time reflecting back to the sensor than others. For instance, we did a scan over some transmission lines in the desert:
|General Topography||400ft (120m)||30%||8 m/s|
|Survey-Grade Topography||200ft (60m)||30-50%||6 m/s|
|200 -225ft (60-75m)||>60%||6 m/s|
|150ft (50m)||>60%||6 m/s|