[Qgis-user] Georeference png files

[Paolo Cavallini]

You can use a pngw. Try saving your map as an image for an example.
Cheers.

On 22 December 2019 17:52:10 EET, Nicolas Cadieux <nicolas.cadieux at archeotec.ca> wrote:
>Hi,
>
>To my knowledge, and I may be wrong, you cannot insert a geotag in a
>.png.  Try saving as .tif. That should be georeferenced.  If you
>absolutely want to use a .png, you will need to create a world file. 
>To see how they work, just export the map window using .png.  A world
>file will be created and will contain the information you are looking
>for.  The world file is a text file that can be opened with notepad++
>or any text editor.
>
>https://en.wikipedia.org/wiki/World_file
>
>Nicolas
>
>> Le 22 déc. 2019 à 10:16, LE LAMER Romain <rlelamer at hotmail.fr> a
>écrit :
>> 
>> Hi,
>> I have a complete map in tiles of 256 x 256 px in png format not
>georeferenced. (if I open them in QGIS they are superimposed on each
>other)
>> 1024 tiles in Longitude and 512 tiles in Latitude = 524288 tiles.
>> Each tile is named as follows: map_Z_X_Y.png
>> Z => zoom (11).
>> X => from 0 to 1023.
>> Y => from 0 to 511.
>> 
>> # If I say no nonsense, I can, by calculation, know the Longitude and
>Latitude:
>> lonN = (360 * (X / 1024)) - 180.
>> latW = 90 - (180 * (Y / 512)).
>> 
>> In the same principle, I can determine the South East coordinates.
>> I know that the whole map is divided into 1024 tiles of 256px in
>longitude, 1024 x 256 = 262144px for 360 ° so a tile = (256 x 360) /
>262144 = 0.3515625 °
>> Same reflection for the latitude, 512 tiles of 256px or 512 x 256 =
>131 072px for 180 ° so a tile = (256 x 180) / 131 072 = 0.3515625 °
>> 
>> lonE = lonN + 0.3515625
>> latS = latW - 0.3515625
>> 
>> How can I add these coordinates to the png file?
>> 
>> Thanks
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-- 
Please excuse my brevity.
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