[Qgis-developer] Georeferencing headeaches

[Andrew Chapman]

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

Andrew Chapman