Convert a .png file to a GeoTIFF while knowing the boundings

Question

Disclaimer: I've already found this link Convert PNG to GeoTiff using GDAL - but it was of no help.

Actually I've got a .png file of a hand-drawn map (I also got it in the .svg format in case this may help). I currently know the exact boundings of this file:

   {
     ne: { lat: 48.506161, lng: -1.714582 },
     sw: { lat: 48.477861, lng: -1.742703 }
   }

It's located in the north of France.

So here's the command I tried so far with gdal_translate:

 gdal_translate -of GTiff -a_srs '+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs'
 -a_ullr 48.506161 -1.714582 48.477861 -1.742703 myfile.png output.tif

My final goal is to serve this file under a tiles system (x/y/z.png) for Leaflet or OpenLayers. So I used gdal2tiles to convert the output.tif file:

sudo gdal2tiles.py -p mercator output.tif  result/

But my problem is that the generated tiles are geolocated in the north of Madagascar instead of France. Any clue on this?

Answer 1

The fact that your map appears at Madagascar and not France is the clue here. It means that your axes are swapped (Madagascar is about as far south as France is West). So you need to switch round the order of the coordinates in your bounding box (and I would use the shorter EPSG:4326 instead of the proj4 string).

So your command becomes

gdal_translate -of GTiff -a_srs EPSG:4326 -a_ullr -1.714582 48.506161 -1.742703 48.477861 myfile.png output.tif