Next up in our “Ask Drone Girl” series is about photogrammetric calibrated drone cameras. If you have a question for Drone Girl, contact her here.
I’m looking for commercial off the shelf, photogrammetric calibrated drone cameras. The only ones I have found are the Phase One cameras. Are you aware of any others?
You stumped me on this one, so I reached out to my friend, Patrick Stuart, who is the Senior Director of Product, Web and Mobile at Skycatch, a San Francisco-based startup that uses software to make commercial drone maps and models processed in the cloud for construction, mining and energy. Here’s what he told me:
“It all depends on the use-case,” he said. “If you need to do millimeter-resolution 3D mesh then, yes, perhaps this would be necessary. For example, you may need to get a 100000% “perfect” 3D mesh of a large statue or something.”
A Phase One camera is going to run you thousands of dollars.
“For normal mapping and surveying it’s complete overkill,” Stuart said. “Use a DJI camera and you’ll be in great shape. Their new 20 megapixel sensors do really good work.”
You can get a 20 megapixel sensor in something as simple as the DJI Phantom 4. In fact, most software that makes 3D maps from aerial photogrammetry, including Pix4D, Drone Deploy and of course Skycatch are optimized for DJI products or other low cost drones –even Parrot’s Bebop.
Readers weighed in too, saying that we’ll also need more information on what type of accuracy you’re talking about — whether it’s relative or absolute.
“Modern photogrammetry is amazing at matching pixels between overlapping photos and, yes, can achieve super high “relative” accuracies, which mean that table in a model will look exactly like the table does in reality,” said reader and drone mapping professional Jon Ellinger. “All the pixels will align very well and it will look just like your table. If you captured the table close enough so that each pixel is about 1 cm then, yes, you can get relative accuracies of about 1-2cm!”
However, there is more to it than just that.
Accorindg to Ellinger, to get super precise absolute accuracy you need survey points or air targets — which will generate what you know as “survey-grade” mapping. You can get this two ways:
- Purchase a drone platform that has very expensive RTK antenna’s on it that triangulate with satellites and known earth base stations
- Use a Mavic or Phantom 4 pro and use surveyed air targets (iron cross pattern works best). Then when processing, you take those surveyed points and “tie down” your table model to precisely where it should be on earth. (This is the more affordable choice and probably better for newbies).
“A mechanical shutter is best, but most photogrammetry engines have built-in correction for rolling shutter artifacts and do well enough for most use cases,” Stuart said. “Skycatch uses a custom-built 20 megapixel mechanical shutter camera on its drones, which produces beautiful maps and meshes.”
Skycatch also makes its own drone that offers centimeter-level accuracy without any ground control points. A standard drone like the Phantom offers accuracy within 500 centimeters, while the Skycatch drone offers accuracy within 5 centimeters. I would also recommend you look into Kespry’s drones, which have a 35mm industrial Sony APS-C Sensor.
However, Ellinger does that a warning:
“In my 10 years working with aerial data I have seen a lot of companies claim crazy accuracy without ground control points but when put to the test have never been able to prove it,” he said.
Other factors involved include flying height and camera sensor resolution, because you’ll never get higher accuracy than the pixel resolution the camera captures.
Ellinger added that if there were just one drone he could recommend for your mapping work, it would be a DJI Phantom 4.
Happy flying, and happy mapping!