In this article, we will cover how to plan a 2D mission, how to reformat the SD card, and best practices for the P4P, including its limitations, and ground control point placement.
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.
Ground control aims to pin your 3D model down to the correct position on the planet. It’s similar to trying to pin a tarp down in high winds. Parts outside of what has been pinned can flap around in the wind, as will long stretches of tarp left unpinned.
1. Find out what coordinate reference system your site is using
Any surveyor or design engineer should be able to provide this information.
- 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.
- 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.
- Fill in the gaps—allow no more than 400 yds (365 m) between points.
- Use all 10 of the AeroPoints—AeroPoint accuracy comes from redundancy, so use all 10.
3. Lay out your ground control according to your plan
- 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.
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. An illuminated green light indicates when it is in the on position.
- Record where you place your AeroPoints - 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).
4. 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 the survey has been completed.
To ensure the best consistency over time, place the ground control points in roughly the same positions (within 10m) every time.
Plan your mission
- Connect the controller to the drone with the USB cable, turn on the controller and turn on the drone - this is for the GPS signal.
- Connect the iPad to the internet - this is for satellite imagery.
- Launch DJI GS Pro v2.0 on the iPad and login to your DJI Account.
- Tap My Missions > blue (+) sign > 3D Map Area > Tap on map.
- Tap on the map to create an initial polygon.
- 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.
The drone will capture data according to the settings you provide, so it’s vital that you set each of them appropriately.
|Question it is asking?
|Skip (changes with drone)
|How should the craft orientate itself when flying?
|We want the camera to take images along the flight path in alternating directions.
|Capture at Equal Dist. Interval
|How the drone should take each photo?
|We want consistent coverage across the site, and we don’t want to waste time and battery by stopping for each image.
|Flight Course 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.
|Skip (this changes according to the other settings)
|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.
|Front lap and side lap
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.
|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.
|Gap between the edge of the area and the flight path.
|There’s no need for any margin.
|Gimbal pitch angle
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.
|Focus every capture (green square)
|AF (auto focus)
|What are the environmental impacts of the area of interest?
|Adjust the setting to reflect current weather conditions. Setting the white balance incorrectly will result in poor stitching and/or inaccurate coloring of your model.
|How quickly should the shutter be operating
|To avoid motion blur. Shutter priority tells the camera that a fixed shutter speed must be used. The camera can adjust the exposure with aperture and ISO. 1000 is usually a good place to start for sunny conditions. In low light conditions, reduce the shutter speed to ~800 and lower the speed.
|EV (Exposure Compensation Value)
|How much of the image should I delete?
|3:2 deletes nothing, utilizing the whole sensor. Everything else deletes data.
|Set to current conditions
|Front LEDs Auto Turn Off
Check the summary information and confirm:
- The photo count is less than 1,000 (for most sites),
- The battery count is correct (generally one battery for every 17 minutes),
- The waypoint count is less than 99 per mission, and
- The motion blur is below 2cm
The summary information is located in the top right of the screen, above the basic/advanced tabs and it scrolls horizontally.
Check that the flight path (the green lines) covers all your ground control points and the area you want to survey.
Save the mission and the defaults (top left of screen).
If the summary shows that these numbers are too high, try adjusting your course angle, overlap, and flight height until they are within the guidelines.
If this still isn’t enough, we recommend splitting your site into multiple missions.
Save your mission
To avoid having to follow this procedure for every mission, we recommend that you save these as your default settings.
Preflight Checks and Takeoff
- Verify you used our recommended best practices for laying out ground control.
- Verify that each AeroPoint:
- Has a clear view of the sky in all directions—avoiding power lines, vehicles, walls, and trees,
- Is on a relatively flat surface of less than 20° from horizontal,
- Is in an undisturbed location during data capture. Avoid locations with any traffic.
- Is turned on to begin collecting data.
Reformatting the SD card:
To reformat the sd card inside the Phantom 4 Pro, connect to your drone, and navigate to the settings option on the app shown below. From there, tap the option Format SD Card.
Phantom 4 Pro limitations, Ground Control Placement, and Differences between Non-PPK and PPK
For a drone that is not PPK or RTK capable, you will need AeroPoints (or ground control points) within your survey area to ensure that the model is accurate. The purpose of ground control points (GCPs) are to tie the model produced by your imagery to known points in the real world.
During the photogrammetry process, the images taken by your drone are stitched together to produce a digital elevation model (DEM) and orthomosaic. However, when your drone takes an image, it records its position within a margin of error of around 10 meters. Although you can still produce a DEM, without ground control, your model will warp and bend.
Think of your site like a tarp on a windy day. You need stakes (i.e., AeroPoints or other GCPs) to keep the tarp (accuracy) from blowing away. If your tarp doesn’t have enough stakes, it will be blown about in the wind. In order to stop this from happening, we recommend that you use at least five GCPs.
Check out our article Best practices for ground control placement in the Knowledge Base to learn more.
The number of GCPs you need is also dependent on how high you are flying and how your site varies in elevation. As a general rule, the GCPs should be spaced in an even grid-like pattern across the site with the following considerations:
- The spacing between ground control points should be approximately twice your flight height. For example, if you are flying at 100 meters (~330 ft) your ground control should be placed in a grid with 200 meters (~660ft) spacings.
- Capture all high and low points, if safe to do so.
- The ground control creates the ‘boundary of accuracy’ for the survey. Anything outside the boundary created by the ground control points should be considered inaccurate.
- Use a minimum of five GCPs.
I still can't do it!
We wrote these articles to arm 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 our support team by emailing email@example.com.