[GRASS-dev] New georectifying module in TclTk

[Glynn Clements]

Michael Barton wrote:

> Shows how little I understand C. This will help to try and follow out the
> various transformations. Mainly I need the affine transformation.
> 
> A question here. Is a single transformation used to generate the projected
> points for RMS error calcuations? Or are different transformations used
> depending on whether 1st, 2nd, or 3rd order is selected?

i.points only understands affine (first-order) transformations, so
that's what the error estimates assume.

The 2nd- and 3rd-order transformations are specific to i.rectify, in
imagery/i.rectify/crs.c.

The problem with higher-order transformations is that you can't
readily invert them, so you can only calculate the error in one
direction.

With regard to your subsequent message:

> > I_compute_georef_equations() and I_georef() are both defined in
> > lib/imagery/georef.c.

-- 
Glynn Clements <glynn at gclements.plus.com>