[GRASS-user] Advice on georectification procedure

[Anna Petrášová]

On Fri, May 13, 2016 at 9:42 AM, Eric Patton <thepattonian at gmail.com> wrote:
> 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.

I don't have too much experience with this, but I think it's a good
approach. But you also need to know the ellipsoid, not sure if that
could cause the misalignment.

Anna

>
>
> Thanks for any thoughts,
>
> --
> Eric Patton <thepattonian at gmail.com>
>
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