Phantom 4 Pro photogrammetry

Why the Phantom 4 Pro is still the reigning king in photogrammetry (with a caveat)

The following guest post about the Phantom 4 Pro for photogrammetry was written by Jon Ellinger, an ASPRS Certified Photogrammetrist and Mapping Scientist in Remote Sensing with over 12 years experience in the aerial mapping industry.  He is currently building a team of pilots as the Remote Sensing manager for the West Coast Land Surveying & Remote Sensing firm, S&F Land Services.

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What if I were to tell you that your iPhone 7 takes better photos than your new iPhone 11?  You would call me crazy.  But in the drone world, there’s a piece of technology that was released in the fall of 2016 that does a better job than similar tech in 2020: the DJI Phantom 4 Pro.  Pair the Phantom 4 Pro with DJI’s GSPro acquisition software, and — when you compare it to other, similarly-priced options on the market in 2020 for aerial mapping — this 4 year old drone is still the best and most popular option for professionals.

The Phantom 4 Pro was a game changer for aerial photography when it was released in November 2016.  It was a quantum leap in combined drone and camera technology that, even today, remains the most sought-after drone for commercial aerial photogrammetric mapping.  A 1-inch sensor with variable aperture on a sub $2000 drone with a 4.3 mile range and obstacle avoidance that could also shoot 4K video at 60 frames per second!?!? The Phantom 4 Pro quickly became the gold standard for anyone looking to use an affordable consumer-level UAV to jump into the drone industry to make a buck. 

Phantom 4 Pro onboard camera 1 inch sensor mechanical shutter
The onboard camera was redesigned to use a 1-inch 20-megapixel CMOS sensor. It’s the first DJI camera to use a mechanical shutter, eliminating rolling shutter distortion which can occur when taking images of fast moving subjects or when flying at high speeds.

The following summer, DJI released their Ground Station Pro software (GSPro) which essentially gave everyone free acquisition software and opened up a new world of opportunity for making money with aerial mapping.  While the best drone mapping businesses tend to be led by people who already have decades of experience working with aerial photogrammetry and a strong technical knowledge of best camera settings, it took the added layer of software and the Phantom 4 Pro for most aerial mapping companies to take flight for cost reasons alone. For small businesses in aerial mapping, all that was needed was access to a high-quality photogrammetry processing software like Pix4Dmapper (which costs $350/month).

Since the Phantom 4 Pro’s launch, we’ve seen a slew of new drones . The Skydio 2’s obstacle avoidance technology is revolutionary.  The Mavic 2 Pro with its 1-inch Hasselblad sensor was called the “Phantom killer” by many in the industry.  The recently released Autel Evo II with its 1 inch sensor, 6K video capability, amazing range and battery life is promising — if you can get your hands on one. 

When I test drones for aerial photogrammetry, I look at both the platform capabilities as well as the mission planning software, specifically the camera controls.  A 1 inch (or larger) sensor with variable aperture is now the standard for professional aerial photography. Nearly four full years later, recent drones finally have caught up with 4K/60fps video capabilities (although the Skydio and Mavic Air 2 have smaller sensors).  I also look at the wind capabilities and range to ensure a strong connection flying larger projects.  

Software matters for photogrammetry missions

Once the hardware is approved I look at the software.  Third-party solutions like Litchi handle waypoint missions extremely well, and MapsMadeEasy MapPilot provides a terrain following solution. But I generally prefer proprietary software provided by the drone company since it has likely been the most tested and vetted for their own platform.  I look for the universal basics – the offline ability to set flight line overlap, design polygon missions (not just rectangle), set AGL, gimbal tilt, etc.  Then I look for the camera settings crucial for successful photogrammetry missions. This is where I often see alternatives to GSPro come up short.

I’ll tell you a little secret.  The best lighting for aerial mapping is overcast.  On a shadowless day, you avoid noise in your final Pix4Dmapper model and will produce a clearer, often more accurate surface model and orthomosaic for your client. 

But, if you are flying below 200ft AGL on a cloudy day with your drone snapping away pictures on “Auto” your photos will likely be rendered useless due to motion blur. That’s because the auto setting of your drone camera software likely set the shutter speed too slow to allow enough light to come in (you can get this same effect by taking a photo out your car window at the passing landscape). 

You can fiddle with your drone speed, lowering it to a point where it takes six batteries to map a 10-acre AOI, or you can provide your customers with the ability to set the shutter speed in the mission planning software. With drones from Autel, the Parrot Anafi, and others, you can adjust a lot of camera settings in their flight apps — but those settings don’t transfer over to their mission planning counterparts. 

DJI Ground Station Pro (DJI GS Pro) Phantom 4 Pro
DJI Ground Station Pro (DJI GS Pro), allows you to conduct automated flight missions, manage flight data on the cloud, and collaborate across projects.

With the Phantom 4 Pro and DJI Ground Station Pro (DJI GS Pro), you have full control within the mission planning app to set shutter or aperture priority for my missions as well as ISO and exposure compensation lock.  GSPro is the only software that provides the nearly the same camera setting flexibility that you’d get with a professional Nikon DSLR. 

Plus, there are added benefits: GSPro software shows estimated photos, acreage, flight time and batteries, tells you which aperture and shutter speed are being used for each frame during capture, and allows you to lock exposure.   I won’t even go into how amazing it has been to be able to create missions and share them within the app to new pilots at our various offices.

The Phantom 4 Pro and GSPro have been around for a long time now and there have been few updates — but that’s not a bad thing. The Version 2 came out with quieter propellers and a slightly better transmission system, but the camera did not change. Similarly, only a few more options have been added to GSPro over the years.

Meanwhile, other companies are catching up.  Autel released their EVO II SDK, which means you can expect third-party mission planning solutions as well their own mission planning software to improve over time.  Even when these platforms do catch up with their flight specs and mission planning software they are all still lacking the one defining hardware spec that still makes the Phantom 4 Pro line king: its global mechanical shutter. 

 

DJI Phantom 4 Pro mechanical shutter electronic rolling camera photo
Comparison image courtesy of DJI

The single greatest reason why the Phantom 4 Pro is king for photogrammetry

I know of no other drone on the market even close to this price range that offers a mechanical shutter.  

The rolling electronic shutters of the Skydio, Parrot, Autel and even the most recent DJI Mavic models simply cannot provide the same level of still photo quality at typical flying speeds that the Phantom 4 Pro can. 

A mechanical shutter exposes each pixel of a sensor simultaneously, whereas a linear rolling shutter exposes each pixel row one at a time.  Pix4D clarifies this by comparing it to a digital scanner or copier machine and states the distance between the first and last pixel line of a sensor could be 1 meter on the ground with typical mapping flight speeds.  This ultimately will lead to motion blur, especially with slower shutter missions on ideal overcast days. 

Even with a robust photogrammetry software like Pix4Dmapper, the small distortion from a rolling shutter sensor will, in the words of Pix4D, hinder “the software’s ability to accurately estimate a camera’s exterior and interior orientation, and therefore its extraction of accurate geometry.”

Simply put, the Phantom 4 Pro will always take clearer photos under the same lighting conditions than even the newest high-tech drones. That’s why, when the Phantom line became unavailable for purchase through most of 2019, there was a scramble amongst mapping professionals to find them. Some sold on eBay for far above their original purchase cost.

The defining mechanical shutter along with the ultra-customizable GSPro mission planning software makes itl the reigning king for affordable aerial mapping… with one big caveat.

The Phantom 4 Pro is made by DJI — a Chinese company.  In the past year, the US government and some private companies have banned use of drones made in China.  In order to satisfy customers, those bans forced companies to search for non-DJI alternatives. There’s the rebranded 3DR Yuneec H520-G; Yuneec is a Chinese company, but U.S.-based 3D Robotics replaces the original software (firmware) with their own version, which satisfies legal requirement). There’s  the Parrot Anafi, made by French company Parrot, and now the Autel Evo II Pro (Autel Robotics does manufacturing in China but operates out of Seattle, Washington).  The alternatives come up short on either the mission planning software side or with insufficient camera control during missions. 

Autel Robotics EVO II PRO 6K Drone Bundle

That said, the Autel Evo 2 Pro, with the exception of missing a mechanical shutter, now has the hardware and flight capabilities advantage.   And, with the  recently released SDK for third parties to build EVO II Pro mapping capabilities into their own mission planning software suites, this platform shows the most promise.  

S&F Land Services has flown over 500 missions with their Phantom 4 Pros.  To see examples of the work produced using the DJI Phantom 4 Pro with Pix4D software, check out their media-rich website or YouTube Channel (please subscribe) to experience some fly-throughs of the data produced for their clients. 

Contact Jonathan Ellinger on LinkedIn  with questions about testing these various platforms against each other — or just to talk tech in general.

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