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Review of the Phantom 4 RTK

The Phantom 4 is a long-trusted and long-loved drone. It was DJI‘s first truly professional drone.

Image Credit: Unmanned Aerial Operations

When the potential for aerial mapping and aerial surveys was put on the table for drones, DJI needed an industry-accurate solution.

The DJI Phantom 4 RTK was born. 

Why I bought the Phantom 4 RTK

My company uses the Phantom 4 RTK on our daily mapping and surveying missions. This is because the Phantom 4 RTK is a compact, reliable, cost-effective drone.

My reasons for purchasing this drone are that I already had used Phantom 4s in the past for photography and lower accuracy surveying and mapping and 3D modeling missions. 

Having these Phantom 4s, I could use the armada of batteries I had for them for the new Phantom 4 RTK. Yes, the Phantom 4 batteries are compatible with the Phantom 4 RTK.

I was happy to find that the remote controller that came with the Phantom 4 RTK was a smart controller. This meant I didn’t have to buy a new tablet or use a smartphone to fly and plan automated mapping missions.

My first impression of the drone Itself was that it was a Phantom 4 with a node on top. Not much to make a fuss about.

However, at its $12,000 price point compared to the Phantom 4’s $1,000 price point, that little node on top is actually a big deal.

Real Time Kinetics (RTK)

The Phantom 4 RTK’s upward-facing node is the RTK unit. This unit is what makes the aerial survey 1000 times more accurate, achieving  0.1′ vertical accuracy.

RTK units use a technology called real-time kinetics to track where a photograph was taken in real-time, referencing the photograph’s location to a local base station that has been calibrated by a land surveyor.

In order to use the RTK node, you’ll need to connect to a base station. However, the RTK node can do more than RTK.

Post Processing Kinetics (PPK)

Not only does the RTK unit on the drone use real-time kinetics, but it can also use PPK, otherwise known as post-processing kinetics.

Post-processing kinetics is what I use because I can put the photos and PPK data into software such as Propeller.

When inserted into Propellor, the information that the post-processing kinetics records gets applied to the aerial mapping mission when we insert the photos into the mapping engine for photogrammetry outputs. 

» MORE: Best Drone Mapping Software

Combining the post processing kinetics and shots that the Land-surveyor takes to double-check our elevations, we produce a survey grade aerial derived map.

Phantom 4s and Phantom 4 RTKs produce aerial maps with what’s called photogrammetry. The Phantom 4 RTK does not have a lighter unit on it.

Therefore, it creates aerial maps by taking a series of photos, usually hundreds to thousands, and overlapping them while at the same time recording the data that we previously mentioned, such as their location. 

Flight performance

In my experience, the Phantom 4 RTK can fly a great distance and, in some cases, beyond visual line of sight. Obviously, this is not legal, so I haven’t tested how far I can go beyond visual line of sight.

However, many of my jobs using the Phantom 4 RTK are on construction sites that have been cleared of any debris woods.

I usually take off from the highest point so that there is no signal interruption.

However, I have been in cases where I wasn’t on the highest point of the construction site, and my signal was slightly lost.

There are two types of signals that the remote controller puts out to the Phantom 4 RTK: video feed and control. I have never lost control of the Phantom 4 RTK on any of my missions.

However, sometimes the visual feed is a little choppy, but this seems to be a common occurrence with Phantom 4s of all models. 

According to some testing done by other pilots, the Phantom 4 RTK can fly more than 4.2 miles in good conditions and still provide a decent video stream.

This is more range than most people can handle without running out of battery or losing visual line of sight.

Although no one has yet to find the cause of occasional video signal drops, it is a minor problem that has not affected the flights in the long run. 

Battery life

The battery life of the Phantom 4 RTK is just about the same as the Phantom 4 standard or Phantom 4 Pro.

Since the drone is the exact same base model, and the only weight added is the RTK processing node mounted on top of the drone, it doesn’t affect flight time severely.

One thing that separates the Phantom 4 RTK  from other Phantom 4 models is the new propellers of the drone.

These propellers can generate more lift with less power, meaning that the flight time, even with the RTK node on top, isn’t extremely affected.

In fact, the Phantom 4 RTK has an extra 2 minutes of flight time over the base Phantom 4. The Phantom 4’s flight time comes in at 28 minutes, while the Phantom 4 RTK  comes in at 30 minutes.

On top of that, the new propellers are quieter. Phantom 4s are known for their extremely loud sound while in flight compared to a smaller drone.

Camera quality

The camera quality of the Phantom 4 RTK is 4K, but this falls slightly behind when put up against other drones, such as the Mavic Air 2, which came out around the same time.

Image Credit: Unmanned Aerial Operations

This is because DJI made the Mavic Air 2 for photography and videography, while the Phantom 4 RTK is made for mapping missions.

Compared to other drones, the Phantom 4 RTK has a wider lens, so we can capture more of the surface that it is attempting to map.

I’ve put it to the test, mapping the same surface with the Phantom 4 RTK and the Mavic Air 2.

To map the same surface as the Phantom 4 RTK, I had to fly the Mavic Air 2 at a higher elevation because while the Air 2’s camera is of higher quality, the lens isn’t as wide.

Should you switch from a Phantom 4 Pro to a Phantom 4 RTK for Aerial Surveying?

The Phantom 4 RTK has the advantage that you need to use fewer ground control points. Their GPS capabilities are the main functional difference between the two data collection devices.

The Phantom 4 Pro’s GPS is consumer-grade and about as accurate as your phone’s GPS (not survey-grade).

The Phantom 4 Pro requires a lot of ground control to anchor and correct it, meaning more work for you and the land surveyor you are working with.

Otherwise, the survey can drift by up to 10′ XY or 50′ vertically.

As mentioned before, the Phantom 4 RTK can achieve 0.1′ vertical accuracy using a single ground control point thanks to the DJI base station and the onboard GPS module.

The DJI base station, paired with Phantom 4 RTK, can calculate image geolocation with high precision but low accuracy when properly deployed, which allows surveyors to set relative accuracy in photogrammetry processing and then shift the entire project to match one ground control point.

This allows for 100% site accuracy and eliminates the need to perform manual ground control or PPK processing.

This results in significant time savings on the field because there are fewer ground control points, as well as achieving higher accuracy in aerial mapping and surveying missions.

If you’re already a Phantom pilot, you’ll have no trouble flying the drone because this drone has identical flight characteristics and drone controls.

Ground control for non-RTK UAVs depends on the drone’s height and the area you’re flying in. Non-RTK drones require 5 GCPs per flight.

As discussed previously, the PPK feature of the Phantom 4 RTK does not require any ground control due to its size or altitude.

The Phantom 4 RTK’s highly precise photo geolocation means that only a handful of GCPs are required to move the entire model. 

If you do decide to use the RTK, it is recommended to set three GCPs. Technically, it is recommended that three GCPs be set for each DJI base station.

The difference in control points required between the Phantom 4 Pro (5-7 acres) and the Phantom 4 RTK (5-8 acres) is negligible.

The Phantom 4 RTK can quickly distinguish itself from the Phantom 4 Pro as the project site grows in size. The Phantom 4 RTK wins if you have sites that are larger than 20 acres.

Some sites have difficult access, making it impossible to shoot in those areas. Perhaps the client is involved in a dispute with a neighbor, making it difficult to access.

Non-RTK projects may have whole quadrants of unreliable data.

Without ground control in the far-flung corners of the project, you will not be able to ensure full-site accuracy, and you will have areas of uncertainty that cannot be used for making observations/measurements.

Ground control is crucial for drones that are not RTK, such as the Phantom 4 Pro.

The Phantom 4 RTK doesn’t care about GCP distribution. This means that if you don’t have easy access to your site, it will not affect the accuracy of your project. So put the GCPs where it’s easy, and you’ll be just fine.

The Phantom 4 RTK drone is more capable than the Phantom 4 Pro if the goal is to create a topographic map or conduct a boundary survey.

It is important to consider the size of your projects and the man-hours spent on ground control. This will help you determine the cost.

If your site is larger than 20 acres, the time savings of shooting fewer ground control points can quickly offset the higher cost of the Phantom 4 RTK.

Final thoughts

Altogether, the Phantom 4 RTK is an excellent drone and well worth it, even considering the relative age of the model.

Perhaps I wouldn’t be saying that if I wasn’t conducting aerial mapping missions on a commercial level.

If you are a pilot who maps small areas, you could probably save some money and stick with your current drone. However, the Phantom 4 RTK Pro will definitely up your game.