Learning to scan

We often used drones and cameras to create 3D models of buildings and places. This page details the protocol for conducting such a scan. However, before you can participate in a drone scan, you should be familiar with (if leading the scan) or in the process of becoming familiar with (if assisting) the following topics:

• RTK GPS - Which we'll use to establish ground control points (GCPs) used to make sure the scan is accurately geolocated.
• Drones - So you know the rules of flying and the technology involved
• Structure from Motion Photogrammetry - So you know the theory and practice behind making a 3D model and orthophoto from a mission.

Eligibility

Flying a UAV a serious responsibility. Operators should have an FAA Part 107 Remote Pilot certification or be with someone who has that certification and is that is ready to take over control of the aircraft. University students without a Part 107 can still fly under the direct supervision of someone with Part 107 certification or independently for educational and research uses under the rules that govern recreational drone operations (49 U.S.C. § 44809) and described in this circular. This includes passing the online TRUST knowledge exam.

Basic rules for students learning to fly

• Fly under 400 feet above ground level (AGL).
• Never fly over people or moving vehicles not participating in the drone operation.
• Always keep the drone in visual line of sight.
• Do not fly within several miles of an airport without special permission.
• Do not fly at night unless you have this endorsement on your Part 107.
• Never interfere with and avoid any manned aircraft.
• Drones above .55 lbs (250 grams) must be registered with the FAA and must have an operating Remote ID.
• You must have your Part 107 certification and proof of drone registration on your person when flying.
• To fly on the Binghamton University campus requires special permission from the office of EH&S. Permission takes 5 business days to secure.
• A full discussion of the rules of flying is well-beyond the scope of a small bulleted point list! It takes a few weeks of study to learn the rules. To operate independently with the supervision of a Part 107 Remote Pilot, you must understand these rules. You can start here to learn to fly as a recreational pilot. You must pass the online TRUST exam and carry proof that you have done so. Students are encouraged to get their official Part 107 Remote Pilot certification.

Gathering Data

Planning

• Check flight restrictions using Aloft online or via an app.
• Use SkyVector, VFRMap, or download official sectionals from the FAA.
• If operating in restricted airspace, you'll need to get clearance to fly. You can do this through the Aloft app or here.
• If flying on the Binghamton University campus, apply for a permit from the EH&S office. Permission takes 5 business days.
• Check for updates on drone firmware. Update as necessary and verify the drone's safe operation during a test flight. (This test flight must also comply with all rules.)

Night Before / Prep

• Check again for firmware upgrades on your drone.
• DJI drones will not operate if in a restricted airspace. Disable flight restriction lock if necessary with DJI's self-unlock website.
• Charge:
  • Controller
  • All Batteries
  • RTK GPS
• Check:
  • RTK GPS connects to someone's Hotspot? It pulls down corrections from an NTRIP server?
  • Weather:
    • What's the expected wind (including gusts), visibility, and temperature?
    • Windy.com.
    • METARs

Packing

• Your Part 107 card
• Batteries
• Spare Propellers
• SD Card
• Landing Pad
• A chair?

Pre-Flight Checklist

• Check the wind speed. We avoid flying if sustained wind speed is greater than 8 kts and gusts are greater than 18 kts, but know your limits as a pilot and don't fly out of your comfort zone. Better to cancel and fly another day than risk your aircraft. Under no circumstances should you fly if the windspeed is greater than 10 kts or gusts are greater than 25 kts.
• Propellers are sound. No cracks, missing pieces, large dings.
• Disable flight restriction lock if necessary.
  • When you get to an area where drone unlocking is required, then you point both joysticks down like you are going to arm the drone. Then a message will pop up that you are in a no fly zone, which you can override by putting in the phone number of the device that is attached to the controller and putting the code into the app when you get it.
• Check RTL height is set correctly. Recommended: 50 m outside. Must be set higher than highest obstacle + safety margin + GPS error.
• Check maximum height is set correctly. Recommended: 120 m, but could change based on surroundings and mission requirements.
• If flying a custom drone, check balance. Are batteries and payload centered?

Post-Launch Check

• Quickly put the drone through a quick flight check. Go to a height of 15-20 feet and aggressively move forward, back, left, right, up, down, yaw left and right. Does it respond correctly?

Before you leave

• Inspect the drone for damage or wear to propellers.
• Consider pulling the SD card and inspecting the imagery, particularly if the field location is distance or reflying another day would be difficult.
• Log all relevant info to the flight log.

Post Flight

• Charge any used batteries to 65% (storage charge)
• Pull the imagery and process the data as noted below ASAP after the flight. Immediately after is best, within 24 hours is good practice.

Processing the Data

• After the flight, you'll copy the imagery from the drone to the PC.
• While you can access images by plugging the drone into the PC via USB, it's better to remove the SD Card, and copy the files over from there. The micro SD cards can be read in some computers directly, or via an SD card adapter.
• A very quick walkthrough is here.

Project Setup

• Set up your folder in d:\projects\pix4d\yyyymmdd_location_drone. Create two subfolders here, a "data" and "pix4d" subfolder. Put images into a data/images subfolder. Use underscores instead of spaces. If you have multiple flights from the same day, separate these into folders by number (data/images/1,data/images/2,data/images/3, etc.).
  • For example, d:\projects\pix4d\20230208_blacksburgPark_mavic2\data\images.
  • Although your images are likely in subfolders in the SD card, you want to pull them over in a "flattened" directory. BE SURE YOU ARE COPYING AND NOT MOVING. It's best to keep everything on the SD Card intact as a backup.
• Set up your Pix4D project following the prompts. You'll generally want to make sure that you're using the Mapping Profile.
  • Save the project to the folder above. For a name, use the location and an underscore-number if processing different flights separately. For instance, d:\projects\pix4d\20230208_blacksburgPark_mavic\pix4d\2blacksburgPark_1.p4d, d:\projects\pix4d\20230208_blacksburgPark_mavic\pix4d\2blacksburgPark_2.p4d

Project Settings

• Select the 3D Mapping profile - Most of these settings are good. For an extended discussion of the settings, see this discussion.
• Note for intermediate users: Pix4D assumes a WGS84 lat/lon geotag input, an EGM 96 GEOID (i.e., orthometric heights), and will produce WGS84 / UTM output. THESE MAY ALL BE INCORRECT so you should review these carefully. We advise to set to ellipsoidal height of 0 for both input images and GCPs, and set the output height to an elevation above the ellipsoid for the site you're working on. You can estimate this by using the NOAA Geodesy API (example). The park at Blacksburg at which we often fly has a geoid height of -31.878. A full discussion of this issue is here for more information.
• DO NOT RUN YET

Step 1

• You'll run Step 1 ONLY first, so uncheck Steps 2 and 3.
• Most settings for Step 1 are good.
• On the Resources and Notifications tab, reduce memory and CPU usage down a few notches. This helps make sure your computer is responsive and usable for other tasks during the reconstruction.
• Run Pix4D Step 1, inspect output, add MTPs or GCPs as necessary. If output looks bad at this point, stop and review SfM guidelines, curvature problems, and especially camera calibration. 95% of the time, it's a camera calibration problem.
• If and only if Step 1 looks good, proceed to run Pix4D steps 2 and 3.

Steps 2 and 3

• On Step 2 -> Point Cloud tab: Save as LAZ not LAS, check box for single file. Uncheck Classify Point Cloud. For a high resolution model (not generally needed!) changed the resolution from Optimal -> High.
• On Step 2 -> Mesh, uncheck Generate 3D Mesh, unless you need it.
• Default Step 3 Settings are generally fine. However:
  • Depending on your application, consider changing resolution from Automated (1 X GSD) to Manual, in which you specify the output resolution of your raster. If flying at 120 meters, your GSD with the Mavic 2 (a 20 MP camera) will be about 3 cm. However, if flying much closer, GSD can be below 1 cm, which may be unnecessary for your application. The higher the resolution, the longer the processing time.

Outputs

• The pix4d project has three subfolders:
• 1_initial - Which contains project set-up, calibration logs, etc. These can be quite useful for diagnosing errors.
• 2_densification - Which contains the LAZ point cloud and mesh (if created).
• 3_dsm_ortho - Which will have the Digital Surface Model (in 1_dsm), orthophoto (in 2_mosaic), and a DTM and other products if created.