UNDERSTANDING NEEDED ACCURACY

You should know the accuracy requirements for any project before you make your flight plan.  Some projects require accuracies as high as 0.02’, which is out of reach for currently available drone surveying equipment.  Others are often OK with 2’ accuracy for rough topographic mapping.  And the operational differences between these accuracies are massive.

There are direct trade-offs between accuracy, ground control, flight altitude, and processing times.  In order to obtain the highest accuracy, you have to fly very low, set a lot of ground control, and take a lot of pictures, which means more time in the field, and more time processing data. If lower accuracy is acceptable for a project, then you can fly higher, set fewer ground control points, and both field time and processing time are considerably shortened.  Because of these tradeoffs, it is generally advisable to fly as high as possible for the level of accuracy required. 

Below is a table detailing the approximate tradeoffs between accuracy, altitude, and ground control.  This table assumes a DJI Phantom 4 Pro with a 20MP camera and no on-board RTK.