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Ground Pixel Size from Camera Geometry

Estimate ground sampling distance from height above ground, physical sensor width, real focal length and image width in pixels.

  • Formula & worked example
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

At 100 m above ground, a 36 mm-wide sensor, 50 mm lens and 6,000-pixel image width give a nominal ground sampling distance of 1.2 cm per pixel.

GSD = height above ground × sensor width / (focal length × image width in pixels)

Worked example

Enter these known values and leave the other values blank.

Camera height above the ground
100 m
Actual focal length
50 mm
Image width
6000 pixels
Physical sensor width
3.6 cm
Nominal ground distance per pixel
1.2 cm /pixel

Assumptions and limitations

  • This is a nadir-view pinhole-camera estimate over locally flat ground. Off-nadir viewing, lens distortion and terrain variation are excluded.
  • Use height above the imaged ground, not altitude above sea level. Use the actual focal length and physical sensor width, not 35 mm-equivalent values.
  • The pixel width must be a positive whole number. The relevant image and sensor widths must refer to the same image area after any cropping.
  • Ground sampling distance describes nominal pixel spacing. It is not a guarantee of survey accuracy, feature detectability or reconstruction quality.

Common questions

Does halving flight height halve the pixel size?

Within this model, yes: GSD is directly proportional to height with the other inputs fixed.

Should I use the camera’s equivalent focal length?

Use its actual physical focal length with the actual physical sensor width. Mixing an equivalent focal length with a physical sensor width gives an inconsistent result.

References

Bookify requires a whole positive image width while preserving the captured camera-geometry equation and inverse calculations.

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