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Net.Noise owner news at
Sun Mar 7 00:47:40 EST 1993

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

In <93Mar4.135222ast.68 at> brian at (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       

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