[GRASS-user] Advice on georectification procedure

[Eric Patton]

Hi list,

What is the best approach to take when georectifying a scanned, projected
map (but the projection is unknown)? Is it necessary to georectify the map
first into a lat-long location and *then* r.proj the map into a target
projection? This is the method I used, using 20 GCPs (reading lat-long
graticule intersections from the map) and a cubic rectification, but there
is still a lot of error (see attached; I overlaid the GSHHG coastline for
comparison).

I'm not sure if I am going about this the correct way.


Thanks for any thoughts,

-- 
Eric Patton <thepattonian at gmail.com>
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