The role of ground control in drone surveying

In traditional drone surveying, you need a sufficient amount of known points to verify and pin down your drone imagery to the ground. This is because a drone without kinematic processing capabilities is capturing 2D site imagery.

When a graphic? Drone Surveyors Dursley  in the sky isn't accurately geotagged, you don?t get reliable positional data from the hardware used to collect the imagery alone; that accuracy originates from ground control. The points used to reference positions on the ground are called ground control points (GCPs), and this can be known points marked and measured with base and rover or a moveable smart ground control point like Propeller?s AeroPoints. In the event that you?re working with known points, a surveyor typically has to physically walk a site, shoot the points with a rover, and mark them for visibility.

Not only will be the mechanics of the process time-consuming, the overall time investment increases dramatically with the website?s physical size. In addition it adds safety risks for personnel who've to walk an active site, traverse hazardous terrain, or access almost unreachable regions of a niche site. (Think dangerous spots, like a 400-foot cliff that could be unstable in a mine.)

What is smart ground control?

If you?re dealing with smart GCPs like AeroPoints, you merely place the hardware in an optimal distribution across the entire surveyed area. That is crucial, much more so than the number of GCPs in a particular location. Essentially, you?d need to develop a shape bounding your website and distribute GCPs using survey guidelines?hitting the lowest and highest elevations.


Once AeroPoints come in place, the procedure becomes infinitely simpler. The AeroPoint is equipped with a GPS receiver collecting locational data throughout the duration of the flight. Activation is only a single-button operation to start logging the data. When your drone survey is complete, pressing the single button again will submit the info to Propeller via WiFi signal, typically a hotspot on a cell phone.

Photogrammetry: how drone images become a 3D survey
At its most basic, ?photogrammetry? may be the science of gathering information about an object or environment through the use of photos. Photogrammetry can be used in drone surveying to measure geography and landscapes by analyzing and processing hundreds or thousands of overlapping aerial photos taken by a drone. When you combine enough overlapping images of exactly the same features, photogrammetry software can be used to generate photorealistic 3D representations of topographic surfaces and features.

As an example, the human eye uses stereoscopic techniques to see in 3D and understand depth. Think about your eyes as two cameras, each taking in a view of one's surroundings from slightly differing angles. If you were to focus on an object before your face and view from each eye individually, you?d spot the object ?moves? location in your vision. When viewing the thing with both eyes simultaneously, the human brain merges both views into a single, three dimensional perspective, creating an impression of depth. This is similar to how drone-based photogrammetry works?however instead of having two cameras on constantly, one camera (on the drone) captures the images as it flies the website, and the photogrammetry software combines those images to generate depth/3D information.

If you took an average image from the survey, you?d easily be able to pick out many ?features? between different photos.  Get more information  match, the higher it is possible to relate images one to the other and reconstruct objects pictured in them.

With  Drone Surveyors Bristol  of these features?think millions?it is possible to create a ?cloud? of points. Each point has a matched feature describing your surveyed area for the reason that location. You can then turn your point cloud into any regular outputs found in geospatial software, just like a 3D mesh or digital elevation model (DEM).


RTK and PPK: What are they and how are they different?
All drone images used a survey have to be reviewed and corrected for positioning inaccuracies. Real-time kinematic (RTK) processing on a drone and post-processing kinematic (PPK) are both workflows used to ensure survey-grade accuracy but work in various ways.

First, a bit of context. RTK describes onboard drone hardware which allows the drone to talk to a base station in real time to validate its location in space. RTK processing means the process of correcting positional information in real-time during the drone flight.

The biggest challenge with RTK processing is that it needs the drone (or rover) to be in constant communication with the base station. Any signal interruption, even momentary, can make significant data loss, which results in inaccurate survey maps. Unfortunately, drones can often lose signal connection for a number of reasons, which makes data unreliable as a result. Terrain, buildings or other obstructions, a decrease in signal strength, or increased distance from the RTK station can all interfere or decrease the reliability of connection between a UAV and its own RTK base stations. Unfortunately, you're likely unaware that disruption has occurred and soon you begin processing the info.

Due to this, drone surveys are increasingly being processed using post-processing kinematic (PPK), which uses a ground control point and an RTK-enabled drone to correct the positioning data after the flight. Following the flight is completed, those two sets of GPS data are matched up using a timestamp, that is recorded when the drone requires a picture. Now that we realize the offset after the fact, the original, less-than-accurate on-board GPS data is then overwritten, giving precise geotags for the imagery. With PPK, you don't have to maintain connection between your RTK base station and the drone during flight. For these reasons, Propeller recommends PPK over RTK for drone surveying on any site, including construction sites, mines, aggregates, and landfills.


Here?s how they stack up side by side:

RTK

Requires stable radio link to receive base station data, which is processed during flight.
Correction data and initialization loss results in reduced percentage of accurate camera positions, that is necessary for site survey rendering.
PPK

No data or initialization loss by signal link limitations, much like RTK technology.
All captured data processed with similar algorithms to RTK, run backwards and forwards through the data.
Overall, ensures the most reliable results possible survey over survey.