In a previous article, we introduced the concept of Ground Sample Distance and discussed why it is important to understand for Photogrammetry applications. To summarize quickly, Ground Sample Distance is the measure of accuracy and will help translate the distances in your images to distances on the ground.
When planning a drone flight to collect data, many pilots will want to determine that they are achieving the correct GSD for their project prior to executing the mission. This article will walk you through how to use QGroundControl, a free program, to plan your flight and determine your Ground Sample Distance.
Download and Install QGroundControl
Download the desktop version of QGroundControl for free here. Once you have installed the program, launch it and move the map to your area of interest. Then follow the directions below to determine your Ground Sample Distance.
Select Units of Measurement
- Launch QGround Control
- To select your unit of measurement (feet vs meters) click on the icon in the top left corner and click on Application Settings. If you change the unit of measurements, you’ll need to restart QGroundControl.
Define the Survey Area
- Navigate the map to your survey location.
- Click on Fly Plan.
- Choose Survey.
- Select your takeoff location by moving the “T Launch” icon into position. Click “Done” on the Takeoff Menu to confirm.
- To define your survey pattern Pattern > Survey.
- Click “Basic” on the Polygon Tools menu. Then drag each anchor to define the edges of your survey area. Add more anchors as needed by clicking on the faded plus icons. Adjust until you are satisfied that the survey area has been adequately defined.
Adjust Survey Settings
- On the Survey Menu, click on the camera icon to choose your camera, lens, landscape/portrait orientation. This provides the focal length and sensor width for your GSD calculation.
- On the Survey Menu, click on the pattern icon and choose your overlap. High-resolution cameras typically require a 60-70% overlap.
- On the Survey Menu, we recommend selecting Options, “Images in Turnarounds” when using Vision Aerial drones for surveying. When this is selected, the camera will take pictures while the drone is turning corners to provide better resolution in the areas that can sometimes be missed.
- Enter your altitude. Once this is entered, you can see your “Grnd Res” which is your Ground Sample Distance. You can toggle between “Grnd Res” and “Altitude” if you want to enter a target GSD. Be sure to check the altitude after setting your ground resolution to ensure you will be at a safe altitude above any obstacles on the ground.
Note: Special Considerations for Your Flight Plan
Once you enter your altitude or “Grnd Res” (Ground Sample Distance), check your Total Mission Distance and Time. If your altitude is very low, you may end up with a very long flight time. Depending on your time and other restrictions, and may need to adjust accordingly. Setting your GSD will be a balance of a safe flying altitude and the time you are able to spend in the field. You may have to make a choice between getting a better resolution or the amount of time you spend flying your survey. Also, you can select a better camera or lens to help improve your survey accuracy.
To Sum it All Up
Ground Sample Distance is an important metric to consider while planning your drone surveys. A lower GSD provides greater detail in your images, however, there are trade offs to consider such as longer flight times and safely avoiding obstacles on the ground. Using flight planning software like QGroundControl will help you determine the appropriate combination of factors before you fly.
Looking for an Aerial Surveying System? Call (406) 333-1795
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