Enter the flight altitude, sensor height, focal length, and image height into the calculator to determine the GSD.

GSD Formula

The following formula is used to calculate a ground sample distance.

GSD = ( A * SH) / ( FL * IH) 
  • Where GSD is the ground sensor distance
  • A is the altitude
  • SH is the sensor width/height
  • FL is the focal length of the camera
  • IH is the image width/length

To calculate the ground sensor distance, divide the product of the altitude and sensor width by the product of the focal length and the image width.

What is GSD (Ground Sample Distance) ?

GSD, short for ground sample distance, is a metric used with drone mapping and surveying to relate the focal length, resolution, and camera distance from the object.

Knowing all but one of any of the variables present in the formula above means a person can solve for the missing variable. The units for GSD are distance per pixel, i.e. cm/pixel.

How to calculate GSD ground sample distance?

The following example problem outlines the steps needed to calculate a ground sample distance (GSD).

First, determine the altitude of the drone taking the image. In this example, the drone is flying at an altitude of 500 feet.

Next, determine the sensor width. Measuring the sensor width in this example yields .75 feet.

Next, determine the focal length of the camera. The focal length for this particular drone is found to be 6 feet.

Net, determine the image width/height. The image footprint on the ground is found to be 100 feet.

Finally, calculate the GSD using the formula above:

GSD = ( A * SH) / ( FL * IH)

GSD = ( 500 * .75) / (6 * 100)

GSD = .625

FAQ

What factors can affect the accuracy of GSD calculations?

The accuracy of GSD calculations can be influenced by several factors including atmospheric conditions, camera quality, lens distortion, and the precision of input values such as altitude, sensor width, and focal length. Ensuring accurate measurements and accounting for potential errors are crucial for reliable GSD estimations.

How can GSD be improved in aerial surveying?

GSD can be improved by using high-quality cameras with larger sensors and longer focal lengths, flying at lower altitudes, and ensuring the camera is properly calibrated. Additionally, using drones with stable flight capabilities can reduce blurring and enhance image quality, further improving GSD.

Why is GSD important in drone mapping and surveying?

GSD is a critical metric in drone mapping and surveying as it determines the spatial resolution of the images captured. A lower GSD value means higher image detail, allowing for more precise measurements and analysis. This is essential for applications requiring detailed geographic information, such as agriculture, construction, and environmental monitoring.