[Qgis-user] Georeferencer

[Richard Duivenvoorde]

On 23/12/2019 09.12, Dave Gardiner wrote:
> Hi Richard
> 
> Thank you for helping. I confirm i followed the process in the webpage
> except for ticking the no projection box. I opened the tif file in a new
> QGIS project and the coords where lat/long = 0.0, 0.0 or there about.
> The coords are correct in the tif.point file. The CRS for both QGIS and
> Referencer were set to WGS84.

Hi Dave,

(please keep the conversation to the list)

Then something went wrong. As I reckon you should have US or EU
coordinates... (not 0.0)..

What did you use as background map to reference your images too?
Are you sure that maps is in WGS84 (as in: you see lat lon coordinates
in the bottom bar of QGIS when you move the mouse?) and you see
EPSG:4326 there?

You can save the GCP file as a small txt file that should should show
you your pixels from your image mapped to the coordinates in your
desired crs. Else can you show that one to here?

Start of with 'Transformation type' Linear: that means no rotation or
warping of your image so if you click one or two coordinates, at least
your map should be in more or less the right position and scale.. If
that succeeds, try the other transformations.

Just to be clear: you will not change your original image. YOu will get
a new (geotiff) file named [originalname]_modified.tif and
[originalname]_modified.tif.points (being the GCP if you checked save
gcp points).

IF you are georeferencing, do you see sane coordinates appear then in
the table below the georefencing map? That is: pixel coordinates
relating to world coordinates?

> For other file formats
> there is a 'world file' created [0]. Did you copy both your world file
> AND the image?
> 
> Where is the World file created, where do i find it and where do I copy
> it to?

Forget about that. I had a look in the plugin, and it always saves the
output in geotiff format.

A world file ALWAYS should sit next to the image it belongs to. If you
want an example, just export the map canvas of QGIS to an image (png),
QGIS will then create an worldfile next to it.
(in the settings there is an option though to always create a world
file, you could check that one and show us here too).

Regards,

Richard Duivenvoorde