[Qgis-developer] Georeferencing headeaches

Andrew Chapman andrew.chapman at donkagen.co.uk
Sun Sep 11 10:52:41 EDT 2011


As far as I can tell, no. I'm aware that there are issues with a previously
georeferenced TIFF, but I'm using a BMP and didn't think that this can store
metadata.

Andrew Chapman
-----Original Message-----
From: Maxim Dubinin [mailto:sim at gis-lab.info] 
Sent: 11 September 2011 15:39
To: Andrew Chapman
Cc: qgis-developer at lists.osgeo.org
Subject: Re: [Qgis-developer] Georeferencing headeaches

Are you trying to georeference a raster that is already georeferenced?

AC> I've used the georeferencer a number of times without difficulty (1.7.0,
AC> Windows) on a number of occasions, but I've run into difficulties a
couple
AC> of times as described below.
AC> I'm trying to georeference a BMP (4804 x 3084 pixels) using four points,
AC> linear nearest neighbour transform and EPSG:27700. The message at the
bottom
AC> of the screen says "Transform:Linear Translation (399639, 182204) Scale
AC> (2.10238e-06, 2.14539e-06) Rotation: 0 Mean error: 1.82928e+06".
AC> The points file contains:
AC> mapX,mapY,pixelX,pixelY,enable
AC>
399725.746871799987275,182064.111945799988462,40058150.943396233022213,-1346
AC> 0679.245283015072346,1
AC>
399773.490492700017057,182058.143993200006662,62315320.754716999828815,-1767
AC> 9358.490566037595272,1
AC>
399756.519127400009893,182072.939542400010396,54779886.792452841997147,-1017
AC> 3018.867924522608519,1
AC>
399763.668237300007604,182090.781233999994583,58678528.301886811852455,-1997
AC> 509.433962255716324,1
AC> The mapX/Y values seem sensible, but the pixelX/Y values are far too
AC> large... and shouldn't they be integers?
AC> It generates the following world file:
AC> 0.000002109413289
AC> 0
AC> 0
AC> -0.000002133093642
AC> 399641.036519734247122
AC> 182094.590552107954863
AC> The raster loads but is about 10mm wide rather than about 200m.
AC> I'm not sure exactly why certain images are a problem, but am starting
to
AC> wonder if it is linked to trying to transform into a relatively small
target
AC> area.
AC> Has anyone else seen this type of problem or is there anyone who can
suggest
AC> where I may be going wrong... or should I just file a bug report?

AC> Andrew Chapman




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