Date: Wed, 05 Jan 1994 16:57:19 +0100
From: olthof@ecn.nl (H. Olthof)
Subject: Re: i.rectify2
response to:----------------------------------------------------------------------------------------------
... old material deleted
Gerald (Jerry) I. Evenden Internet: gie@charon.er.usgs.gov
----------------------------------------------------------------------------------------------I have both vector data and rasterdata in my lat-lon mapset. I made the
coordinate transformation from ll-->lcc for the vector data with
v.proj. For the raster data I used i.rectify2 as described. Now, if
you make an overlay in the lcc mapset. (the vector map over the raster
data) they don't fit. They are shifted up to tens of kilometers. in
some of the Greek islands, the 'vector island' and the `raster island`
don't even overlap! In order to check my results I have transformed a
vector map (with v.proj) and a raster map which was derived from this
vector map (In the lat-lon mapset, using v.to.rast) I would expect that
both maps would fit exact in the lcc mapset, as they did in the lat-lon
mapset. But no.... So either v.proj is not accurate (but since this is
a coordinate transformation for which the transformation formulas are
known, I have assumed that my vector data are correct) Or, i.rectify2
is not accurate enough. (which I can understand, because the area is
large and i.rectify only makes a fit, for the transformation matrix).
Or, I am missing something and there is an other solution for this
problem.
I suspect that your second supposition is the problem---i.rectify2 .
To check v.proj you are better to compare it to proj of PROJ.4 or
GCTP but not against i.rectify.
The clue also seems buried in the "transformation matrix" but since
I have no experience with i.rectify I can't be of much help other
than to note that it must be *much* more than a simple scale-rotate-
shift operation. That is, i.rectify2 must know all about lcc
to be able to create a complex non-linear transformation.
Any i.rectify2 gurus out there?
Gerald (Jerry) I. Evenden Internet: gie@charon.er.usgs.gov
voice: (508)563-6766 Postal: P.O. Box 1027
fax: (508)457-2310 N.Falmouth, MA 02556-1027