## Photogrammetry, Inventory and Model( FOR 4360 )## Scale DeterminationA common task in Aerial Photogrammetry is to determine the scale of an image. This method can be applied to aerial photographs or photocopies maps that may have changed scale from the original.
Scale is a function of two factors first is the focal length
The scale formula is usually expressed as: $$ S= \frac{f}{H-h} $$ Where This information is not always available. An alternative using similar triangles is to use: Where Scale is usually expressed as a fraction such as 1:24,000 the scale of a USGS 7.5 minute topographic map. If you applied the above formula to the USGS 7.5 minute topographic map you would get 0.000042 which is the decimal equivalent of 1:24,000. to make it easier to produce the fraction we usually calculate the Photo Scale Reciprocal (PSR). |