The GSD is the real-world size of a pixel in your images, and for most drone flights it’s between one and 10 cm. A low GSD (1cm) is very high resolution imagery, and a high GSD means lower resolution.
The GSD is determined by:
- The resolution of your camera sensor — e.g., a 12MP camera will have a higher GSD than a 22MP camera
- The altitude of your flight — flying higher means a higher GSD
- The focal length/field of view of your camera — a wider angle camera like a GoPro means a higher GSD
In general, the final accuracy for a model in X and Y is one to two times the GSD, and one to three times in the vertical however you will find that the average error tends to be closer to one times the GSD for all axes.
Image source: Doug Corrin, Maps and Photogrammetry