What is GSD and why is it important for drone surveys?

Ground sampling distance is a measure to specify the resolution or detail of a drone survey or drone map.

Ground Sample Distance (GSD) is the real-world size equivalent to a pixel measurement in a digital image. In surveys, drones hover over and produce a series of such images from a specific height, which together make up maps of areas. These images are obviously not life-sized. They are representations, and in order to be useful their scale must be available. The scale (or value we use to convert image size to real-life size) is based on the height of the image and the width of the image among other possible factors. For example, if we want to know the distance in meters from one point to another based on a digital image captured by a drone, we would assess it first in terms of pixels. Let’s say the distance is 345 pixels. Having a GSD conversion value of .75 cm/pixel, we would calculate that the distance in meters is (.0075 m x 345 =) 2.5875 m. Survey accuracy depends directly on GSD value. Lower GSD conversion values avail more precise measurements and allow for measurement of smaller areas and objects.