Calculate ground sample distance (GSD) or a missing camera value from altitude, sensor dimension, focal length, and image size in pixels.

GSD Calculator

Enter any 4 values to calculate the missing variable






GSD Formula

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

GSD = ( A * SH) / ( FL * IH)
  • Where GSD is the ground sample distance (distance per pixel)
  • A is the altitude above the ground
  • SH is the sensor width/height (a physical sensor dimension)
  • FL is the focal length of the camera
  • IH is the corresponding image width/height in pixels (px)

To calculate the ground sample distance, divide the product of the altitude and sensor dimension by the product of the focal length and the corresponding image dimension (in pixels).

What is GSD (Ground Sample Distance) ?

GSD, short for ground sample distance, is a metric used with drone mapping and surveying to relate camera height above the ground, camera/lens parameters, and image resolution to the real-world ground distance represented by a single pixel.

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 (cm/px).

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 120 meters above the ground.

Next, determine the relevant sensor dimension (width or height) for the direction you are computing GSD. In this example, the sensor width is 13.2 mm.

Next, determine the focal length of the camera. The focal length for this example is 8.8 mm.

Next, determine the corresponding image dimension in pixels (width in pixels if you used sensor width, or height in pixels if you used sensor height). In this example, the image width is 5472 px.

Finally, calculate the GSD using the formula above:

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

GSD = (120 m * 13.2 mm) / (8.8 mm * 5472 px)

GSD ≈ 0.0329 m/px (≈ 3.29 cm/px)

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.