[GRASS-dev] New georectifying module in TclTk

[Hamish]

Maciek Sieczka wrote:

> > > It sounds like most of the issues can be avoided by using
> > > i.rectify -c.
> > 
> > that is my understanding.
> > 
> > > What are the disadvantages of using the -c switch?
> > 
> > you have to restart GRASS in the target location and set up the
> > region by hand. Ok if you knew to project a v.in.region box first
> > and can calculate your target resolution
> 
> Could you say how to calculate it?

1) XY to meters:
see "Introduction to GRASS software" by Markus Neteler, 1998 2nd ed.,
part VI, section 1.1.1 (p.27)


2) lat-lon to meters:
1852m per nautical mile
60 nautical miles per degree lat
width of degree lon goes as cos(lat)

so
dist_m_ns = dist_deg * 1852*60
dist_m_ew = dist_deg * 1852*60 * cos(lat)

and

res_ns = dist/rows
res_ew = dist/cols

see also "g.region -e"


Hamish