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Newsgroups: info.grass.user
Path: zorro.cecer.army.mil!shapiro
From: shapiro at zorro.cecer.army.mil (Michael Shapiro)
Subject: Re: rectification
Message-ID: <C3I83F.9rD at news.cecer.army.mil>
Sender: news at news.cecer.army.mil (Net.Noise owner)
Organization: US Army Corps of Engineers Construction Engineering Research Labs
References: <93Mar4.135222ast.68 at ug.cs.dal.ca>
Date: Sun, 7 Mar 1993 05:47:39 GMT
Lines: 22

In <93Mar4.135222ast.68 at ug.cs.dal.ca> brian at ug.cs.dal.ca (Brian  Kierstead) writes:

Affine transformation:
	x' = ax + by +c
	y' = Ax + Bt +C

The a,b,c,A,B,C are determined by least squares regresion based on the
control points entered.  This transformation applies scaling, translation
and rotation. It is NOT a general prupose rubber-sheeting, nor is it
ortho-photo rectification using a DEM, not second order polynomial, etc.
It will really only works well if (1) you have geometrically correct images
and (2) the terrain or camera distortion effects can be ignored.

>	This may not be an appropriate question, it's more math, but how does
>i.rectify work? I realize it's a matrix transformation but what is the theory 
>behind this?
>						-brian
-- 


Michael Shapiro U.S. Army CERL
Environmental Division