rectification problems

[Nick Cahill]

We are having problems rectifying rasterized contour maps. 
The raster maps consist of one-pixel-wide contour lines, and 
we are rectifying them into a UTM coordinate system; we 
then want to run r.surf.contour on the rectified map. We 
have found, however, that when we rectify, the contour lines 
become discontinuous -- occasionally pixels drop out, 
leading to problems with r.surf.contour. Does anyone know 
a way either to ensure that pixels do not drop out in 
rectification, or to fix slightly discontinuous lines in a 
contour map without editing them by hand (the maps are 
large, > 5k x 5k). Unfortunately it is probably impossible to 
import them as vectors and then rasterize them in GRASS; 
we would much rather import the large raster files. Any help 
would be greatly appreciated. Thanks --

Nick Cahill
Perseus Project
nick at ikaros.harvard.edu