DRONE MAPPING ON THE CHEAP - Harvard University

DRONEMAPPINGON THECHEAPFaineGreenwoodSignal Program, Harvard HumanitarianInitiative

In the past three years, drones have gone fromobscurity to ubiquity, thanks in large part toinexpensive sensors developed for mobilephones.Drones are now being used around the worldfor a wide variety of remote sensingapplications, and their popularity is onlyincreasing as they become ever moreinexpensive and easy-to-use.

Drone MappingDrones have proven useful for mapping, as acomplement (or substitute) for aerial mapping andsatellite imagery.Strengths include: Inexpensive (less than 1000 to buy someuseful mapping platforms) Ability to gather both still photos and video Ability to operate under cloud-cover Modular – can use multiple sensors (And more)

How does drone mapping work?The drone has a camera (or other sensor) toshoot images, and a small GPS unit whichlets it know where it is in space.Aerial maps are made from many imagesthat are combined using photogrammetrysoftware.The pilot either flies the drone themselves(manually) or uses a program that flies thedrone autonomously.

Multirotor DronesSmall multirotor drones like the DJIPhantom 3 Professional can bepiloted autonomously and are easyto learn to use. They look lessthreatening than larger drones, andcan be purchased or builtinexpensively. Newer models geotageach photograph they take.

Fixed-WingFixed wing drones resemble conventionalairplanes, and are often used for largemapping jobs. Some people build their own(for as little as 500), while others buy offthe-shelf models (at many price points).

We made this model at the Medfield MentalHospital outside Boston, using the DJI Phantom3 Professional drone and Drone Deploy software.The map and 3D model spans 22 acres and used172 photos. We flew 246 feet above the groundfor all vertical images.

These 3D models can be manipulated and“flown” through, like a video game map.

We can use the same geo-referenced photographs tomake an orthorectified and georeferenced 2D map,using photogrammetry software. We achieved a GSD(detail level per pixel) of 3.2 CM, flying 246 feet abovethe ground.

Drone Mapping Steps: FlightPlanning

Flight Paths/Resolution UAV flight paths need enough forwardand lateral photographic overlap, allowingpost-processing software to identifycommon points in each image. (Softwaredoes this for you now). 60% overlap is agood minimum figure. Resolution in aerial photography is measuredas ground sampling distance (GSD)—thelength on the ground corresponding to theside of one pixel in the image, or the distancebetween pixel centers measured on theground (these are equivalent) – or, the levelof detail in each pixel. (This is also calculated

GSD Equation GSD (pixel size x height aboveground level) / focal length.A Canon S100 lens, zoomed out, has a focallength of 5.2 mm (26 mm zoomed in).So if we wanted, say, to be able to resolve 1cm-sized features on the ground using azoomed-out S100, we would have to fly at:1 cm x 5.2 mm / 0.0019 mm 27.3 m 89.7feet

Illustration Valerie Altounian

UAV Image Outputs forMapping Two-Dimensional : Orthorectified,georeferenced maps, generated frommany still vertical (nadir) aerialphotographs. Three-Dimensional – Digital Surface(DSM/3D models, viewable in Autodesk,generated by photogrammetry softwarefrom many vertical and oblique images.(And volume measurements).

Some Common ProcessingSoftwareDesktop: Agisoft Photoscan Pix4DCloudbased: DroneDeployOpen-Source: VisualSFM

Ground Control Points/RTKSurveyors use high-accuracy ground controlpoints (often measured with a surveyor grade dualfrequency RTK GNSS receiver) to align dronegenerated maps with real world measurements.10 GCPs are often enough, an improvement overthe 1000 points required w/ traditional surveying.Some drone manufacturers, like Trimble andSensefly, sell RTK-GPS enabled drones thatstreamline this process – potentially enablingabsolute accuracy down to 3 CM.

Drone Mapping Uses: There’sLots!Drones are being used for mapping work around theworld and in a variety of different professions.Archeologists Miners Farmers Architects Construction Planners Wildlife Researchers .and many more.A database is available at drones.newamerica.org.

Peru Archeological UAVMappingIn March and April of 2015, I traveled to Peruto observe the archeological drone mappingwork of the Peruvian Ministry of Culture.There, a government funded UAV program hasused drones to map hundreds of archeologicalsites in both 2D and 3D. They use DJIoctocopter and hexacopter UAVs, and AgisoftPhotoscan photogrammetry software.

Disaster Mapping in VermontJarlath O’Neil-Dunne of the University ofVermont’s Spatial Analysis Lab has used aSensefly eBee fixed wing drone to do smallscale disaster mapping.He believes drones will be particularly usefultools for small communities that lack thebudget to afford manned aircraft or satelliteimagery.

Great, But is it Ethical?Ethical standards in the use of drones arestill being developed. Some of the mostcommon concerns include: Privacy Data Security Safety Community Involvement And more!

Privacy How do we protect the privacy of peoplebeing photographed from a drone? Can we identify individuals from the droneimagery? How does our drone imagerycompare to imagery taken from Google Mapsand other public services? How do we convey what we are doing topeople who we may be photographing? How can we use social media to tell peoplewhat we are doing?

Data Security Who do we share the data we collect with? What should we do about drone data thatmight be used to harm innocent parties? How do we make sure we collaborate withpeople who share our values? What do we do if our drone inadvertentlydetects illegal activity or other unintendeddata?

Safety How do we ensure we fly as safely as ispossible? How do we mandate that pilots arecompetent and well-trained? What do we do if a drone crashes? Whatdo we do if it harms somebody? What kind of insurance should droneoperators carry?

Community Involvement How do we inform communities of what weare doing? How to involve them in theprocess? How do we convey what we’re doing topeople in different cultures and in differentlanguages? How do we work with communities to ensurewe’re gathering data that they can use, andthat they are comfortable with? Are we flying the drone because we want to,or because communities can use and benefit

New America DronePrimerIn July 2015, NewAmerica released aprimer to civilian drones,co-authored byKonstantin Kakaes andmyself.You can read it for free atdrones.newamerica.org.

Signal Program at HHIThe Signal Program will be incorporatingdrone technology into its existinghumanitarian-focused work with satellites. Weplan to release new research on drones forhumanitarian purposes in many areas,including ethics, practical applications, tool-totask match guidance, and more.We also will be holding a remote sensingworkshop at Harvard in June.

Any Questions?I’m available to talk about drones and dronemapping.Get in touch with me at:fainegreenwood@gmail.com

CHEAP Signal Program, Harvard Humanitarian Initiative. . thanks in large part to inexpensive sensors developed for mobile phones. Drones are now being used around the world for a wide variety of remote sensing applications, and their popularity is only increasing as they become ever more inexpensive and easy-to-use.