Notes

The role of ground control in drone surveying
In traditional drone surveying, you will need a sufficient amount of known points to verify and pin down your drone imagery to the bottom. For the reason that a drone without kinematic processing capabilities is only capturing 2D site imagery.

When an image?s position in the sky is not accurately geotagged, you don?t get reliable positional data from the hardware used to collect the imagery alone; that accuracy comes from ground control. The points used to reference positions on the floor 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 dealing 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 are the mechanics of this process time-consuming, the entire time investment increases dramatically with the site?s physical size. Not to mention that it adds safety risks for personnel who've to walk a dynamic site, traverse hazardous terrain, or access almost unreachable regions of a niche site. (Think dangerous spots, just like a 400-foot cliff that may be unstable in a mine.)

What's smart ground control?

If you?re working with smart GCPs like AeroPoints, you merely place the hardware within an optimal distribution across the entire surveyed area. This is crucial, a lot 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 best practices?hitting the cheapest and highest elevations.



Once AeroPoints are in place, the procedure becomes infinitely simpler. The AeroPoint is equipped with a GPS receiver collecting locational data through the entire duration of the flight. Activation is a single-button operation to start out 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 elementary, ?photogrammetry? is the science of gathering information regarding an object or environment by using photos. Photogrammetry is used in drone surveying to measure geography and landscapes by analyzing and processing hundreds or a large number of overlapping aerial photos taken by way of a drone. Once you combine enough overlapping images of exactly the same features, photogrammetry software may be used to generate photorealistic 3D representations of topographic surfaces and features.

For example, the eye uses stereoscopic ways to see in 3D and understand depth. Think about your eyes as two cameras, each taking in a view of your surroundings from slightly differing angles. In the event that you were to focus on an object in front of your face and view from each eye individually, you?d notice the object ?moves? location in your vision. When viewing Drone Surveying Bristol with both eyes simultaneously, the human brain merges both views into a single, three dimensional perspective, creating the feeling of depth. This is much like how drone-based photogrammetry works?however rather than having two cameras on constantly, one camera (on the drone) captures the images since it flies the site, and the photogrammetry software combines those images to create depth/3D information.

If you took an average image from a survey, you?d easily manage to pick out many ?features? between different photos. The more features you match, the better you can relate images to one another and reconstruct objects pictured in them.

With a lot 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. After that Drone Surveying Bristol can turn your point cloud into any regular outputs found in geospatial software, 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 need 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 make sure survey-grade accuracy but work in various ways.

First, a bit of context. RTK describes onboard drone hardware that allows the drone to talk to a base station instantly 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 create significant data loss, which results in inaccurate survey maps. Unfortunately, drones could lose signal connection for a number of reasons, which makes data unreliable because of this. Terrain, buildings or other obstructions, a decrease in signal strength, or increased distance from the RTK station can all interfere or reduce the reliability of connection between a UAV and its RTK base stations. Unfortunately, you are likely unaware that disruption has occurred until you begin processing the info.

For this reason, drone surveys are increasingly being processed using post-processing kinematic (PPK), which uses a ground control point and an RTK-enabled drone to improve the positioning data after the flight. Following the flight is completed, those two sets of GPS data are harmonized using a timestamp, that is recorded when the drone requires a picture. Now that we realize the offset after the fact, the initial, less-than-accurate on-board GPS data is then overwritten, giving precise geotags for the imagery. With PPK, there is no need to maintain connection between your RTK base station and the drone during flight. Therefore, 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, that is processed during flight.
Correction data and initialization loss results in reduced percentage of accurate camera positions, that is essential for site survey rendering.
PPK

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

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