Is the DJI Phantom 4 RTK Worth its Salt?
As far as the appearance is concerned, the DJI Phantom 4 RTK resembles the original Phantom 4 but appearances can be deceiving. Along with the evident difference, the price tag, the two machines are quite different from each other. Firstly, Phantom 4 is essentially used by cinematographers and low key enterprise projects. Secondly, the Phantom 4 RTK, is a beast of a machine when it comes to precision aerial mapping – a low elevation aerial sensor that claims to have centimeter-accurate data while needing minimal ground control points. Despite the jaw-dropping price tag of $6,500, you get an incredible value for this whopping amount of money.
Do you need the DJI Phantom 4 RTK?
RTK is the acronym for Real-Time Kinematic and is used in reference to a satellite navigation approach that can amplify the accuracy of position data retrieved from satellite centric positioning systems such as GPS and GLONASS.
Yes, you hear us right, it is centimeter-accurate! Drones used for cinematography or search and rescue do not have to be pinpoint accurate with regard to their location. If the image is a bit to the left, you can always crop it. So, there is no need to spend money on such a case and stick to your old drone. But when it comes to precision aerial mapping, every centimeter is of great significance. This drone provides you just the requisite accuracy at a price that has blown away the minds of experts as they expected a far higher price tag.
A post from the drone mapping company Pix4D states that the DJI Phantom 4 RTK has brought about a complete paradigm shift. Keep in mind that the Pix4D does come with a few stakes in the product as images obtained via the Phantom 4 RTK can be processed in any of the software developed by Pix4D. The post, however, goes onto say that while RTK had been available in fixed-wing drones for some time or the enthusiastic DIYers could augment PPK or create a tailor-made RTK copter, the recently released DJI Phantom 4 RTK is the first machine integrated with RTK technology and priced so reasonably. Similar to all other DJI products, it is available in RTF shape. You simply need to get your batteries charged up, get your account registered, and then set your drone whizzing through the sky without having to solder components or attach wires and cables
History of precision mapping drones
The DJI Phantom 4 RTK was released globally in October 2018. Before its arrival, drones were used for precision mapping but it was considered a burdensome and rather costly affair. About 40 ground control points (GCP) per square kilometer had to be configured by operators to derive the requisite amount of data at the desired precision level and it could take a lot of time to replace the ground control points. With the help of the DJI Phantom 4 RTK, the number of ground control points needed is dramatically reduced to zero which according to the manufacturer, tends to save up almost 75% of the precious time. Job Ellinger, a drone mapping professional and the creator of TLT Photography, which is a pioneer in aerial surveys and geospatial data processing, underscored an in-depth guide on drone spatial resolution and accuracy just a couple of years back.
At that point in time, most photogrammetry software could attain about 2-3x the GSD in relative accuracy. This would have required the use of a licensed surveyor with air targets or much more costly tech and equipment.
So, that meant either:
1. Acquiring a drone that comes integrated with costly RTK antennae that triangulate with satellites and identified earth base stations
2. Deploy a Mavic or Phantom 4 Pro and use surveyed air targets. Subsequently, during processing, those survey points are retrieved and the table model is strapped down to exactly where it is on earth Companies such as Skycatch did offer such solutions that claim that its drones offered accuracy up to 5 centimeters. Similarly, Kespry claims to have drones equipped with a 35mm industrial Sony APS-C Sensor. Both of these are headquartered in the San Francisco Bay Area and offer subscription models that begin at over $1,000 a month. Phase One, a Denmark based company, offers subscriptions that range between $28,950 and $65,600.
How is Phantom 4 RTK different from Phantom 4?
Phantom 4 RTK is loaded with an RTK module that provides real-time, centimeter-level positioning data. Accuracy of 1cm+1ppm (horizontal), 1.5cm+1ppm (vertical), and 5cm absolute horizontal accuracy of photogrammetric models can be provided by the RTK module of the DJI Phantom 4 RTK.The drone is also equipped with a redundant GNSS module that helps the drone stay stable in regions where connectivity can be a bit of an issue such as populated cities. The two modules work in tandem to maximize flight safety and ensure that precise data is derived from complex surveying, mapping, and inspection techniques.
The DJI Phantom 4 RTK’s positioning system can also be connected to a D-RTK 2 Mobile Station, NTRIP (Network Transport of RTCM via Internet Protocol) using a 4G dongle or WiFi hotspot. The satellite observation data can also be used for Post Processed Kinematics (PPK). Michael Cutfield, a Northern Express Group Survey Manager, tested the accuracy of the drone and shared it in this LinkedIn post. He concluded that the drone produced results with a mean Root Mean Square (RMS) error of just 1.6cm on the X-axis, 1.8cm on the Y-axis, and 4cm on the Z-axis.
Other features of the Phantom 4 RTK
The controller is specific to the DJI Phantom 4 RTK thanks to a hidden USB slot which is loaded with a vodem stick for connecting to the internet (the SIM card is furnished by the user of course).
Here are some of the other distinct features of the controller:
• micro-SD card slot
• built-in speaker
• hot-swappable batteries
• Network RTK with a 4G Dongle
• GS RTK App pre-installed
Time sync: This feature enables the operator to consistently align the flight controller, camera, and RTK module while benefitting from the positioning modules. According to the manufacturer, this feature allows for more accurate metadata and stamps the positioning data to the center of the CMOS to help attain centimeter-level positioning data.
The Phantom 4 RTK comes with an inbuilt 1-inch, 20 megapixel CMOS sensor along with a mechanical shutter to prevent rolling shutter blur. It can attain a Ground Sample Distance (GSD) of 2.74cm at 100 meters flight elevation.
The DJI Go 4 app has been designed for the Phantom 4 but the Phantom 4 RTK comes with its own GS RTK app. The app offers a couple of planning modes – Photogrammetry and Waypoint flight – to enable pilots to choose the drone’s flight trajectory while manipulating stuff such as overlap rate, altitude, speed, and camera parameters. The app also allows the user to load directly KML area files for in-house flight strategizing, a new shutter priority mode to keep exposure consistent across all images, and a formidable wind alarm to warn operators about inclement weather prospects.
SDK Support for Phantom 4 RTK:
If you want to add your innovation to the platform, the DJI Mobile SDK lets you work in your magic and do your bit in terms of automation and customization.
How to purchase the Phantom 4 RTK?
This is yet another domain where the DJI Phantom 4 and Phantom 4 RTK tend to be different from each other. The DJI Phantom 4 is readily available at Best Buy or Amazon but the RTK version is not. The New York based camera store B&H Photo is your best bet for purchasing the DJI Phantom 4 RTK. However, here’s the rub: the store only sells the DJI Phantom 4 RTK with D-RTK 2 GNSS Mobile Station which means that you will have to be willing to spend no less than $11,000. If you were looking to get your hands on the D-RTK 2 GNSS Mobile Station, that would be okay since that is more or less the same price you will be paying to any dealer but if you are not looking to get your hands on the D-RTK GNSS Mobile Station, then this is quite exorbitant considering that you will be paying for something you don’t need.
The standalone Phantom 4 RTK costs just $6,500. The B&H kit is quite useful as it bundles together the mobile station with a tripod and a Nanuk hard shell travel case which costs more than $200.
Nevertheless, the DJI Phantom 4 RTK and D-RTK GNSS Mobile Station are available through authorized DJI Enterprise dealers throughout the world. If you are not interested in purchasing this gem of a machine via a dealer, you can get it directly from DJI by filling out this form.