Gridded affine transformation and rubber-sheeting algorithm with FORTRAN program for calibrating scanned hydrographic survey maps

A FORTRAN program is presented for transforming from digitized pixel locations in a scanned map to actual geographic coordinates based upon an affine transformation with rubber-sheeting corrections applied to the digitized nx by ny node grid. The program was developed and successfully applied to over four hundred hydrographic fairsheets and sounding charts from which depth soundings were being read. In addition to correcting for the effects of copying and scanning, the transformations can directly extract geographic coordinates with minimal error from large-scale maps using geographic projections such as Mercator, Gnomonic, and Lambert Conformal. (C) 1997 Elsevier Science Ltd.