In order to turn a set of [src, dest] coordinate pairs into an affine
transformation, you have to solve a system of linear equations. The
solution is the entries in the require affine transformation matrix. In
order to fully determine an affine transformation you need 3 control
points and their images under the transformation.
I don't know if PostGIS has this functionality available, but if you can
hack Java (so to speak) JTS provides a class called
AffineTransformationBuilder which can do this.
Dylan Beaudette wrote:
I have a problematic TIGER module - i.e. a single county in Ca is really
messed up. I thought that a simple translate() would do the job, but it looks
like there is both a translation and rotation involved. I do not really
understand the postgis manual entry for the affine function.
How would one go about converting a series of coordinate pairs ([good], [bad])
into the terms of the affine transform matrix?
thanks,
--
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022
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