[Qgis-user] Re: World file and Georeferencer

[Agustin Lobo]

Manuel,
I use world files with rotation to have a fast albeit just
approximately georeferenced display of images
acquired by a little uav. Those that are really interesting are
further georectified, but for a
first overview the world files with rotation are very useful.

In this case the problem is different. We got a geotif image with
wrong georeferencing (including a rotation)
but being at a very high resolution, we did not notice it and went on
digitizing some interesting features over
the raster. In order to avoid repeating the digitizing, we wanted to
create the world file for the raster
and use the same matrix to warp the vector with Geoprocessing/Affine.

Agus

An example here:
https://sites.google.com/site/filestemp2/home/anye0179_1.jpg
https://sites.google.com/site/filestemp2/home/anye0179_2.jpg

On 11/03/2011 10:51 AM, Manuel Massing wrote:
>
> Hi Agus,
>
>
> > I often need a world file including rotation, would it be possible
>
> > that the Georeferencer plugin had the option of writing a world file
>
> > for order 1 polynomial? (perhaps it is possible for Helmert also, as
>
> > the scaling could be done by modifying the resolution?).
>
> >
>
> > Also, what do you understand by Linear? As far as understand, Helmert
>
> > and order 1 polynomial are linear also.
>
>
> yes, 1st order polynonmials and the 2D helmert transform are linear transforms, so this would be possible.
>
>
> World-file export is currently not enabled for helmert+1st order because
>
> rotated world-files are not always well-supported, even by qgis. It would be
>
> quite bad to create files which are not supported by the originating
>
> application.
>
>
> But maybe rotated imagery works better with the new accelerated warping code?
>
>
> bye,
>
>
> Manuel


2011/11/3 Agustin Lobo <alobolistas at gmail.com>:
> Maxim,
>
> I often need a world file including rotation, would it be possible
> that the Georeferencer plugin had the option of writing a world file
> for order 1 polynomial? (perhaps it is possible  for Helmert also, as
> the scaling could be done by modifying the resolution?).
>
> Also, what do you understand by Linear? As far as understand, Helmert
> and order 1 polynomial are linear also.
>
> I've tried with option Linear, but the transformation does not include
> rotation. I do not know if this is intentional (i.e., a narrower
> definition of linear) or perhaps a bug (rotation parameter is not
> correctly saved to the world file). In other words, the image is not
> rotated if I select Linear (both with and without world file) but
> it's rotated if I select order 1 polynomial (but what I need is the
> world file).
>
> Note world files are ready for rotation parameters:
> http://www.omg.unb.ca/~jonnyb/processing/geotiff_tifw_format.html
> http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009t00000028000000
>
> Also, could the pluging output the parameters of the transformations
> (linear or not)?
>
> Thanks!
>
> Agus
>