GRASS georeferencing a scanned map

GRASS|GRASS

References:


 * Open Source GIS: A GRASS GIS Approach. Third Edition

Version: GRASS GIS 6.4.2

The scanning resolution
The relationship between the distance on the ground and the corresponding length of a raster cell is determined by the scanning resolution.

Assuming a scanning resolution of 300dpi (dots per inch), the equivalent in centimeters is:

118.11 dots per cm (1 inch = 2.54 cm)

Supposing a scale of 1:25000, the on-ground length of a raster cell is:

25000 / 118.11 = 211.6 cm/dot = 2.116 m/dot

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