If you are not accustomed to survey techniques, this is a quick tip for speeding up visits to repetitive sites.
The AirGon Loki Direct Geopositioning system is a huge time saver when it comes to drone survey work. Loki reduces or eliminates the need for ground control points (but please, always have a reliable way of checking the data!!). Loki requires a local base station for post-processing. The usual approach is to place a base station and do static observations for a long enough period of time to process a location solution. In the USA, the typical approach is to observe for at least 30 minutes (two hours is better) and use the National Geodetic Survey’s Online Positioning User Service (OPUS) to obtain a statistically bounded base location. This location is subsequently used in AirGon’s ASPSuite post-processing solution to tie Loki derived positions to the geodetic network.
If you are repeatedly visiting the same site, you can avoid the OPUS process by setting a permanent base monument/benchmark and always setting the base on this mark. We have found that a few bags of Quikrete poured into a Quikrete form tube (all available from Lowes) makes an excellent, stable monument. Paint a photogrammetric target in black and white (using concrete paint) on the finished surface and you are good to go. Use OPUS on installation to establish the location of your monument and simply use these coordinates in ASPSuite for the base station location on subsequent flights.
While you have out the paint, you can place permanent markers in a few locations to use as checkpoints to ensure all went well with your Loki “control-less” flight. Equipment pads and weigh station decks make good locations for these permanent marks. If you don’t have RTK gear for surveying these in, just use your static base station and OPUS (or the equivalent of OPUS in your country). Each time you complete processing a point cloud and ortho in PhotoScan (or your point cloud software of choice), measure the checkpoints using LP360 (sUAS license level).
Using the above procedures, you can bound your drone survey accuracy using industry accepted statistical best practices.