Flying a Photogrammetry Survey

Once you’ve planned a survey over your site it’s very easy to fly it. The only thing you really have to do is put the drone in the air.

Pre-Flight

I usually start by setting up the controller and tablet before putting the drone together, so I’m not wasting the drone battery while I check the settings.

Open the DJI GSP app and select your mission from the list. Choose the edit option to open it, even if you aren’t going to make any changes, though it’s always worth double checking the parameters.

You’ll need to set the switch on the top left of the controller to ‘F’ mode, rather than the usual ‘P’ used in DJI GO. This ‘function’ mode allows the drone to receive a set of instructions to execute while flying.

If you’re happy with the mission settings, set up the drone in a suitable spot to take off from and turn it on. The controller should pick it up and show its details in the top bar of the GSP app. A green line running along the bottom of this shows the remaining battery life, with the estimated time.

pre_flight_app_bar

Don’t forget to calibrate the compass. This can be done in the menu in the top right corner of the app.

Starting the Survey

Start the motors and lift the drone off the ground manually. At this point I’ll always take it up to the same altitude as the survey, and check it has plenty of clearance over any obstacles.

While it’s hovering there the GSP app will now show the drone’s location, a dotted marker to the start of the survey path, and the home location. You can now upload the survey and start the mission using the blue flight button in the top right. This shows you a checklist of requirements to look over before starting.

mission_checklist

Most of these should show green. Though the ‘End-Mission Action’ item is displayed as a warning if the action is return to home (RTH). This is probably to remind you of what the RTH altitude will be before you start, in case it needs to be changed.

You may notice in the first few seconds of the checklist being opened that the data is transmitted to the drone. Once this is complete you can select start to fly.

Survey Flight

The autopilot then takes over the drone and completes the survey. You won’t need to take over manual control again if you’ve chosen the end of mission action to be RTH.

At first the drone will adjust its altitude to that set in the survey parameters. It will then fly to the survey starting point and orient itself before proceeding along the survey lines.

As it travels along you’ll hear the shutter sound on the tablet to indicate each photo being taken. I’ve had two surveys where this sound stopped for one of the mission lines. I thought this was just the sound effect not playing on the tablet, and that the photos would be there later. But when I processed the images there was a missing line in each case. I’m not sure why it happened, but it’s only a rare occurrence, and the high lateral overlap compensated for it. Just keep in mind, if you stop hearing the shutter for a large portion of the survey, you may want to repeat it.

You can follow the progress of the flight on the map in GSP. As the drone moves along the survey, the completed sections of the pathway change colour.

mission_progress

If necessary you can tap the red pause button in the top right to regain manual control of the drone. When you want to resume the survey, just tap this button again and the drone will return to its last completed point and continue.

At the end of the mission the drone will execute the end of mission action. In most cases I set this as RTH at an appropriate altitude for the site. Though sometimes I just set it to hover so I can land it manually if the landing area is a tight fit. Even if you’ve not set the final action as RTH, you can still trigger it with the lower button on the left side of the GSP interface.

After each mission finishes it’s marked as complete in the app’s list. I usually keep them there so I can refer to the parameters later.

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