Making maps with the help of small UAVs seems to be easy enough. However, when geometric accuracy is critical, how do you determine and state the estimated accuracy of your mapping product? One way is to establish a test bed with a redundancy of accurately surveyed check points which are used as independent bench marks against which the map can be compared. In this picture we show a comparison between high accuracy GPS derived check point coordinates and corresponding coordinates as derived from our 3D model. Note that for illustration purposes the horizontal errors were scaled by a factor of 1000.
The 3D model was created from 261 aerial images (13mm GSD) captured by a Sony a6000 camera with 16mm fixed lens. The camera was carried by a Pixhawk equipped modified Steadidrone quadcopter. The flying time was 10 minutes and, using our V-Map system (http://www.microaerialprojects.com/v-map/ ), we could accurately survey the 12 ground control points in about 15 minutes.
Using 105 check points in our error analysis we can now confidently claim that when we map similar terrain with this particular method we can realistically expect to achieve the following accuracy:
Horizontal approximate circular error at 95% confidence 0.028m
Vertical Accuracy at 95% confidence: 0.039m
Not bad, especially when considering that the 4.75ha map can be delivered the very next day after image acquisition.