Relation between the printing scale and the GSD

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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).
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