Zero GCPs: How DJI's Phantom RTK makes Drone Surveying Highly Accurate

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Zero GCPs: How DJI's Phantom RTK makes Drone Surveying Highly Accurate

Surveying and mapping is hard work, you're out in the sun all day squinting through a viewfinder. Just you and your trust total station battling nature and sore muscles- must be better than complicating the status quo with GPS and unmanned aerial systems- Right? That's where you'd be wrong. What if I were to tell you, introducing advanced surveying tools like drones is not going to complicate your workflow. Let's take a look at how using DJI's Phantom 4 RTK with the D-RTK 2 ground station can save you a lot of time, money and body pain while keeping things simple.
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Let's break this down- what would be the typical workflow when running a Survey and Mapping mission using the P4RTK

  • Site Visit

  • Planning

  • Execution

  • Processing

Site Visit

You always start your mission with a Site Visit. In this phase your main objective is finding an ideal drone take-off and landing location. You're also looking out for anything that may pose a threat to the drone flight. This could be transmission lines, high-rise buildings, construction equipment and generally any obstacles. But, since in this situation we're using the Phantom 4 RTK the environment and obstacles are more permissive. The small sized frame of the P4RTK allows you to get away with a smaller or more narrow take-off and landing spot, and the drone can safely and reliably operate in more complex sites.


Mission Planning

Mission Planning or plotting your flight path is incredibly easy with the P4RTK. You can import a KML file directly onto the controller which can then automatically plot the flight path. Once generated we just had to edit the settings to meet our exact needs. In our case we were mapping an open desert. Homogeneous surfaces can be challenging for photogrammetry- so we bumped up our overlap and side-lap to ensure data accuracy. Alternatively, you can even plot the flight path completely on the P4RTK's controller. The benefit is you don't need any additional software to plot your flight path. You just need the necessary KML file from Google Earth or simply just plan it on the controller.


Execution

There isn't much to say about this phase- and that's a good thing. We set up the D-RTK 2 Mobile Station and link it to the Phantom 4 RTK. Then you place the drone down at the designated take-off spot and let the P4RTK do the work for you. The drone will autonomously take off and start it's mission. Once it's done capturing data the drone automatically lands in the designated spot. The biggest time-sink in aerial surveying and mapping is the time required to set up GCPs (Ground Control Points), using the P4RTK with the D-RTK Mobile Station lets you skip the GCPs while retaining a high accuracy level. Say in a complex worksite, or a site within a city it may be hard to find a large enough space for drone take-off and landing. Not for the P4RTK though, making it the perfect drone for small-scale projects especially within the city or in complicated sites.


Processing

Once the survey is done, it's a simple task of pulling out the SD card and importing the data into the DJI Terra Software for processing. Terra's quick calculations will allow you to get comprehensive and precise measurements in any environment with detailed 2D orthomosaics. The images were captured from an altitude of 50m using no GCPs but just the D-RTK Mobile Station. The P4RTK yielded a GSD of 2 cm and horizontal and vertical accuracy of 4 cm and 5 cm. DJI Terra has phenomenal processing speeds- the software can process about 400 images from the P4RTK using just 1GB of RAM. Additionally, since DJI Terra is an offline software, it further saves time by avoiding the need to upload data to the cloud.

DJI's Phantom 4 RTK is a boon to surveyors in an urban setting, or in the case of small to medium sized fields. The small frame of the drone coupled with its simple workflow makes it incredibly easy to integrate into your workflow. Get yourself a Phantom 4 RTK and start saving time and money. What's even better is, get the D-RTK Mobile Station to produce great results without the use of GCPs.

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About the author

Niiveth Mani
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