[Talk-ca] Using ImportImagePlugin in JOSM

[Stewart C. Russell]

Hi Peter,

It's been a while since I hand-rolled a world file. If you can, install
a recent version of QGis, as it has a truly excellent georeferencer. You
click on control points on the bitmap, indicate the coordinates they
represent in the real world, then set the system off transforming the map.


> The map file is called map.jpg and I have created a world file called
> map.wld

I'd call that map.jgw, which is the convention for JPEG world files.
(TIFF has tfw, PNG pgw, and so on.)

> 100.0
> 0.0
> 0.0
> -100.0
> 103.5
> 1.5

Ooh, that can't be right. Lines 1 and 4 are units/pixel; if you're using
geographic coordinates, that's 100°/pixel. This wants to be a small number.


> Can you give me reasonably correct values for my world file?

Lines 1 and 4 might want to be 0.01 and -0.01 respectively for 100
pixels/degree.

> Do I need to create a projection file

It helps, but these are even harder to produce by hand than world files.
I think that QGis can produce them in the georeferencer.

 Stewart