Relation between the printing scale and the GSD

When the final output has to be printed, the printing scale has to be defined. The typical output to be printed is the orthomosaic as it serves as a map. Common scales for printing an orthomosaic:

  • 1:1000
  • 1:500
  • 1:200
  • 1:100
  • 1:50
  • 1:10 (small objects)
  • 1:5 (small objects)
Example: When the orthomosaic is printed on a scale of 1:200, it means that 1 cm in the paper represents 200 cm in reality.

The printing scale indicates the acceptable error that a printed orthomosaic can have. The acceptable error is based on the smallest difference that a human can distinguish at a drawing, which on a scale of 1:1, is about 0.25 mm. This error should be multiplied by the printing scale to calculate the acceptable error that a printed orthomosaic should have.

Example: For a printing scale of 1:200, the acceptable error is 0.25 * 200 mm = 50 mm = 5 cm.

The acceptable error defines the GSD that should be obtained for the project. The GSD should be at least 3 times smaller than the acceptable error. For more information about the GSD: Ground sampling distance (GSD).

Example: For a printing scale of 1:200 and an acceptable error of 5 cm, the GSD should be 5 / 3 cm = 1.7 cm. There is no problem if the GSD is smaller (1.5 cm, 1 cm, 0.5 cm).