Phantom 4 RTK vs Phantom 4 Pro

From Phantom 4 Pro to Phantom 4 RTK, is it worth it?

The Phantom 4 RTK took the drone survey world by storm in 2019. Now, midway through 2020, the Phantom 4 RTK continues to fly off the shelves; most official DJI Dealers find it difficult to keep the Phantom 4 RTK in stock. So what is all the hype about? Is the Phantom 4 RTK worth the higher price tag?

Why is the Phantom 4 RTK different?

The main advantage of the Phantom 4 RTK is that you will need to shoot fewer ground control points. The major functional difference between these two data collection devices is their GPS capabilities.

The Phantom 4 Pro has consumer-grade GPS which is about as accurate as the blue dot on your cell phone (i.e., geolocates photos poorly). So, with the Phantom 4 Pro, you need a lot of ground control in order to anchor and correct the model, otherwise, you can be off by 10' XY and maybe 50' vertically.

On the other hand, the Phantom 4 RTK can get you 0.1’ vertical accuracy with a single ground control point because of the onboard GNSS module and the DJI base station.

When deployed properly, the DJI base station paired with the Phantom 4 RTK is capable of calculating image geolocation with high precision, but low accuracy. Aerotas has developed a workflow that enables surveyors to lock the relative accuracies in photogrammetry processing and shift the entire project to match a single ground control point. This ensures full-site accuracy without the need for manual PPK processing or ground control distributed throughout the entire site. Fewer ground control points translate to significant time savings in the field.

Added Benefits of Making the Switch

Familiarity

For those who already fly a Phantom 4 Pro, the airframe and controller of the Phantom 4 RTK will be virtually identical in form and function. The only difference is that the Phantom 4 RTK has a top hat (the onboard GNSS module).

The drone controls and flight characteristics are exactly the same for both drones.

Efficiency

As mentioned above, the Phantom 4 RTK offers much more precision than the Phantom 4 Pro and thus requires less ground control to anchor and correct the model.

For a non-RTK bird, the amount of ground control required for a job is a function of the height you fly at and the size of your site. About 5 GCPs per flight battery is a good metric to use for non-RTK.

For the Phantom 4 RTK, the amount of necessary ground control is not a function of size and altitude at all. Due to the highly accurate photo geolocation, the Phantom 4 RTK only needs a few GCPs per project in order to shift the entire model. We recommend three GCPs per project, regardless of size. Technically, we recommend setting three GCPs each time the DJI base station is turned off, reset, or moved.

EXAMPLE

100-acre topo | aiming for ~0.1’ vertical accuracy

100-acres flown at 200’ AGL with a Phantom 4 Pro would require at least 25 GCPs.
Alternatively, you could get away with shooting one GCP if you were flying the same mission with the Phantom 4 RTK.

For visualization purposes, you can think of a rubber sheet and a glass sheet. The model created by the Phantom 4 Pro is a lot like a rubber sheet, and the ground control are like tent stakes that tie the model down in the corners and the center. By contrast, the model created by the Phantom 4 RTK is more akin to a glass sheet with holes where the control points are, and that glass sheet must be positioned correctly so that the control lines up.

On smaller sites (5-10 acres) the difference between the Phantom 4 Pro and the Phantom 4 RTK is negligible in terms of the number of control points needed. But, as the size of the site increases, the Phantom 4 RTK quickly differentiates itself from the Phantom 4 Pro. If you work on sites larger than 20-acres, then the Phantom 4 RTK is the clear winner.

Map Inaccessible Areas

Some sites have inaccessible areas that make shooting control in that section impossible. Or, perhaps the client is in a less than neighborly dispute which makes access tricky. As a result, non-RTK projects can have entire quadrants with unverifiable 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. With a non-RTK drone, like the Phantom 4 Pro, ground control quantity and distribution is critical.

However, the Phantom 4 RTK does not care about GCP distribution, so if you do not have access to remote parts of your site, this will not impact the full-site accuracy of your project.

Mooooove your ground control somewhere else, or use the Phantom 4 RTK.

Is it worth it?

If the stated goal is to produce a topographic or planimetric survey, then the Phantom 4 RTK is a more capable drone than the Phantom 4 Pro.

The main benefit is that you will get the same accuracy with fewer ground control points. The only drawback is that the Phantom 4 RTK is more expensive -- it costs five times as much as the Phantom 4 Pro.

The best way to evaluate the price is to consider the average size of your projects and how many man-hours are spent shooting ground control. If you work on sites larger than 20-acres then the time savings from shooting fewer ground control points is very real and can quickly offset the increased cost of the Phantom 4 RTK.

You should make the switch if...

You fly 20+ acre sites
and/or
You frequently fly difficult to access sites

If you would like to discuss ways to improve your drone program Aerotas is here to help.

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