Planning a Photogrammetry Survey

The first thing I looked for when I got the brief for my summer project was a mission planner to control the drone and automate the camera operation. That way the photo coverage of a site would be much more even than if I was manually triggering the shutter.

A student on a similar project in previous years used UgCS to prepare and execute a flight. But both myself and the university have iPads that we take to sites, so we needed something Apple compatible. As the drones are DJI, I looked into their own Ground Station Pro app instead.

It’s very intuitive and simple to run. Here are the steps I’ve followed to plan surveys at some other students’ sites.

Create a New Mission

Select “New” from the bottom left corner of the mission list. There are three types of mission the app runs. For a photogrammetry survey you want “3D Map”.

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Choose “Tap” at the next prompt to set the bounds of the survey area. You’ll need to locate your survey area on the map before bounding it. Use the map buttons in the top right to locate yourself and switch between different map layers. The default map is an unlabelled satellite image. If you need road, town, or city names to locate the area you’ll need to switch it over.

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Define the Survey Parameters

Tap on the map to start defining the survey area. Initially there are four points you can drag into position, but you can add others using the plus symbols on the survey boundaries.

survey_boundary

You’ll see that the app starts to plot a pathway inside the area for the drone to follow¬†using default survey values. Change these in the panel on the right to whatever you need. My parameters usually look something like this:

survey_parameters

In general I’ve tried to have percentage overlap as high as possible for both forward and lateral, and used the time interval capture mode at 2 or 3 seconds. I’ll then adjust the altitude of the survey to shorten the flight time if necessary, making sure the plan leaves enough battery to return and land. Sometimes you won’t need to adjust the course angle, if the pathway in your given area looks reasonable.

Bear in mind that the estimated flight time may change during a flight if the drone has to work against strong wind. Your flight altitude will also need to be higher than any terrain point or objects within the boundary. So try to figure out what your minimum altitude will need to be while planning. This makes planning a bit more difficult in high relief areas compared to a flat site.

Remember to name the mission plan a name at the top of the parameter panel. And save it once you’ve finished. Areas you have already browsed to will be cached, so you won’t need a mobile data connection in the field.

I’ll take some screenshots of the app during the next flight and write a separate post about flying the drone with the survey.

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