How to Plan a 2D Photogrammetry Mission with the Mavic 2

This article provides recommendations to yield the best photogrammetry results if using DJI’s Mavic 2 is your only option for surveying. However, we do not recommend the Mavic 2 for mapping purposes.

The Mavic 2 can capture great images and videos for media purposes, but it uses a rolling shutter that severely limits its use for photogrammetry. A rolling shutter makes it seem like a single photo is taken from multiple locations (because the drone is moving). This can lead to issues with warping, scaling, and noise. This makes photogrammetry more difficult and increases the likelihood of an inaccurate survey.

As always, the quality of your model is based on high-quality photos and ample ground control.

Simply put, the Mavic 2 uses a rolling shutter that is not good for photogrammetry. To mitigate the effects of a rolling shutter, two main changes to data collection are required from a standard (mechanical) shutter:

Changing the capture mode to ‘Hover and Capture’
Manually flying the drone toward the center of the site and taking oblique photos once the main mission is complete

Hover and capture

When the drone is set to ‘Hover and Capture’, the drone completely stops and takes a photo before moving to the next position (mechanical shutters can take photos while the drone is moving). This can address the warping issue that the rolling shutter produces.

Manually flying and oblique photos

We also recommend manually flying the drone toward the center of the site with the camera at a 60 degree angle after the mission is complete. This helps Propeller improve the calibration of the camera and build a much better model. We will explain this in more detail below.

Before leaving the office

The more you can accomplish in the office, the less stress you’ll experience in the field.

New AeroPoints? Activate them before use.
New drone? Set it up following DJI’s videos.
Check flying restrictions for your site and follow the law. There are tools that will help in the USA, Australia, and globally.
Charge and update your drone, controller, and iPad.
- Connect the iPad to the controller with the USB cable, turn both on and open DJI Go 4 on the iPad.
  - Short press, then long press the power button on the controller.
  - Turn on the drone. Always power the drone on after the controller.
    Short press, then long press the power button on the drone.
  - Follow any prompts to update until a live stream from the drone is active with no warnings.
    This step is complete when the top left of the Go 4 app on the iPad looks like this:

Shut everything down once everything looks OK.
- Turn off the drone—short press, then long press the power button on the drone. Always power the drone off before the controller.
- Turn off the controller—short press, then long press the power button on the controller.

Plan your Ground Control

Find out what coordinate reference system your site is using.
Any surveyor or design engineer should be able to provide this information.
Plan the ground control distribution.
1. If you are using a local grid or are not covered by the Propeller Corrections Network, an AeroPoint will need to be placed on a known point.
2. Lay out sufficient ground control and use our Best Practices for Ground Control Placement.
  - Place ground control in every corner and around your site.
  - Place ground control at the top and bottom of any large elevation changes.
3. Fill in the gaps. Allow no more than 400 yds (365 m) between points.
4. Use all 10 of the AeroPoints. AeroPoint accuracy comes from redundancy, so use all 10.
Lay out your ground control according to your plan.
1. To place an AeroPoint on a known point - place the AeroPoint stencil precisely over the known point, then place the AeroPoint on top of the stencil.
2. Each AeroPoint needs:
  - A clear view of the sky in all directions. Avoid power lines, walls, and trees.
  - To sit on a relatively flat surface—less than 20° from horizontal.
  - To remain undisturbed during data capture. Avoid any traffic, if possible.
  - To be turned on to begin collecting data. A green light is illuminated when in the on position.
3. Record where you place your AeroPointsm - use Google Maps, a GPS app, or take pictures of where you put them. This can also be useful to keep for future surveys (see below for why).
Record the time you finish placing your last AeroPoint. You will need to ensure that 45 minutes have passed before picking this back up after completing the survey.

To ensure the best consistency over time, place the ground control points in roughly the same positions (within 10m) every time.

Please see our Best Practice for Ground Control article for more detailed information.

Plan your mission

1. Download DJI GS Pro 2.0 on your iPad.

2. Connect the iPad to the internet to obtain satellite imagery.

3. Launch DJI GS Pro v2.0 on the controller and login to your DJI Account.

4. Tap My Missions > blue (+) sign > 3D Map Area > Tap on map.

5. Tap on the map to create an initial polygon.

6. Adjust the polygon to encompass your site by adjusting the points. The app will automatically generate a flight path (green lines) to cover the area you select.

Setting	Set to	Question it is asking?	Reason
Camera Model	Skip (changes with each drone)
Shooting Angle	Course Aligned	Which way should the craft orientate itself when flying?	We want the camera to take images along the flight path in alternating directions.
Capture Mode	Hover and Capture	How the drone should take each photo?	We want the drone to stop and then take a photo to limit the effects of the rolling shutter. This takes longer and uses more battery but produces much better photos for photogrammetry.
Flight Course Mode	Scan Mode	Can the drone leave the blue flight area?	If it’s set to Inside Mode, it’ll force it to create a flight path that stays within the area, which can be inefficient.
Speed	Skip (this changes according to the other settings)
Altitude	~80m	How high above your launch position should the drone fly?	This will give a ground sampling distance (GSD) of ~0.9in (2.4cm) per pixel, which is low enough for most applications.
Go to Advanced Settings
Front lap and side lap	~75% If you need to reduce one, reduce the side lap (no lower than 60%).	How much should each image overlap with other images?	This will give enough overlap for some missing or poor-quality images and still build a contiguous model.
Course angle	This varies with every flight Experiment with different values until the green flight path is in line with the longest side of the blue flight area.	What angle should it draw the green flight path in your area?	You want to minimize the number of waypoints (turns) the drone needs to complete for battery and time efficiency.
Margin	0	The gap between the edge of the area and the flight path.	There’s no need for any margin.
Gimbal pitch angle	-90 This means straight down	What angle should the camera be pointing, relative to horizontal?	You should always start with straight down (nadir) imagery.
End mission action	Return home at 80m	What should it do once it’s finished collecting data?	Once it’s finished the mission, you want it to return home at the same height it’s been flying or higher.

Set up the camera

1. Switch to the camera screen by tapping on the camera feed on the bottom right of the map screen.

2. Change the yellow circle to a green square and ensure that Auto-focus (“AF”) is selected, rather than “MF.”

3. Tap the settings button, go to the camera tab and change the image size to 3:2.

4. Tap the iris icon and tap “S” to change the shutter speed to 400 or higher.

5. Switch to the map screen by tapping on the map in the bottom right of the camera screen.

6. Check that the blur is lower than 2cm. If it is too high, make the shutter faster (bigger number).

7. Make sure that the home position is correct. If it is wrong, you could easily lose the drone.

8. Send the mission to the drone by tapping the blue airplane on the top-right corner of the screen.

9. Wait for all of the checks to turn green. If they don’t turn green, read the message and troubleshoot the problem.

10. Double-check for any obstructions. If it’s safe to take off, start the mission.

Instructions on flying manually to capture oblique images toward the center of the site.

1. Change the flight mode P>S>P. This will stop the automated mission from returning to home.

2. Make sure the camera view is open in GSPro.

3. Manually fly the drone toward the edge of the site, then turn the camera in towards the center of the site at approximately a 60 degree pitch angle. (don't include the horizon in the image if possible).

4. Slowly fly the drone towards the site's center and intermittently capture an image using the button on the controller or iPad, whichever is easier, every 2-4 seconds depending on how fast you are flying. You don't need a large number of obliques.

5. Once you have a few obliques captured, you can press the RTH button to return the drone to the launch point

I still can't do it!

We wrote these articles to equip you with everything you need to get the job done on your own, but we understand that sometimes this isn't sufficient.

If you're stuck, the Propeller hardware support team may be able to help. You can contact them by emailing hardwaresupport@propelleraero.com.au.

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