Photogrammetric Mapping
Photogrammetry is the process of creating accurate two-dimensional and three-dimensional maps or models using an array of overlapping photographs of an area or object. In 2024, we started the creation of photogrammetric maps for each reserve owned and/or managed by the East Keswick Wildlife Trust (EKWT). The intent of the EKWT Mapping Project is to make these maps accessible to EKWT membership and others via the existing EKWT website.
The Drone
Initially, the project utilised a DJI Mavic 2 Zoom drone, owned by the author, capable of flying semi-autonomous preprogrammed routes. In 2025, this drone was superseded by the DJI Mavic 3 Enterprise (M3E), also owned by the author, which offers significant improvements beneficial to mapping work.
The most notable enhancements of the M3E are its upgraded camera and the Real-Time Kinematic (RTK) GPS add-on, which can provide survey-quality location accuracy. This is discussed further below.
The main camera captures 20-megapixel photos and is somewhat unique in that it has a mechanical shutter. The mechanical shutter dramatically lowers ground blur caused by the motion of the drone and allows the missions to be flown at higher speeds thus reducing battery consumption and allowing longer missions.
The RTK add-on, coupled with an RTK base station, allows the drone to know its location to within a centimetre or so, as opposed to the normal 3-6 metres of GPS accuracy.
There was, of course, a learning curve during the initial mapping efforts which will be obvious as members compare the map layers, but those inconsistencies are being reduced as we progress.
Missions originally designed for the Mavic 2 Zoom are compatible with the M3E, although certain flight adjustments are automatically made by the software to take advantage of the newer drone’s enhanced capabilities.
The ability to reliably repeat missions remains a critical part of our mapping strategy. Repeatability greatly increases the efficiency of our mapping efforts. It also maximizes the accuracy of map overlays so that comparing maps over the years or decades will be more pleasant for any interested member because accurate map overlays will enable much easier visual comparison of changes over time.
Location Accuracy
Photogrammetry depends, in part, on the accuracy of the geographic information embedded in the photos taken by the drone. The source for this geographic information is the Global Navigation Support Systems (GNSS), comprising GPS (American), Beidou (Chinese), GLONASS (Russian), and Galileo (European), and two others that we do not use. GNSS normally has an accuracy of between 3 and 6 metres. This is simply not good enough to provide the accuracy needed for our purposes, so we added technology to our toolbox that dramatically improves GPS accuracy, allowing us to pinpoint locations to within 1cm.
The technology is called Real Time Kinematic, or RTK. The approach was to install a GNSS RTK base station. By placing the antenna of the base station in an already known location, the base station can then measure the errors being broadcast by the many GNSS satellites that are used for location determination. The base station then sends out real time corrections via the Internet that allow RTK-compatible receivers to have very precise location information. These RTK corrections are useful up to about 35km away from the base station, more than enough to cover all the EKWT reserves. In addition, the base station corrections are made publicly available for use by any farmer or construction firm that might need RTK services within 35km of East Keswick. During setup, the base station is calibrated using utilities provided by the Government of Canada for precise positioning of such stations.
It is worth noting that most public domain maps are only accurate to within 3 metres, so the RTK-based EKWT maps will align precisely with one another, but likely be offset slightly when overlayed on public maps.
The Mapping Software
We currently use Maps Made Easy, an affordable mapping service operated by Drones Made Easy, based in the United States. Maps Made Easy also provides Map Pilot Pro, a specialised software for drone control, which enables the planning, saving, and execution of semi-autonomous drone missions across the various reserves.
Depending on the size of each reserve, capturing the necessary images for mapping can require anywhere from several hundred to over a thousand individual overlapping photos. After collection, these images are uploaded to map processing software, which then processes them over a period that can range from just a few hours to more than ten hours, depending on the dataset’s complexity.
This mapping software produces a variety of outputs, several of which are useful in supporting comprehensive documentation of the reserves. We will talk about a few of these later in this document
Recently, we have also been experimenting with mapping software called WebODM, for Web Open Drone Map. The results have been so good that we’ve decided to ultimately move to that application for future map processing. In the meantime, we will use the 3D models created by WebODM as they become available. Over time, all map/model processing will be migrated to WebODM.
Conclusion
We are still in the early stages of this project, and it is very likely that there will be changes in tools and/or approach over time. We do hope, though, that members of the EKWT will find the efforts worthwhile and beneficial in achieving the objectives of the Trust.