2

I have a mapoverlay in a custom projection which I need to add as a layer to an Openstreet map within a website. Since I was not able to change the projection earlier, I decided to manipulate the raster image in Photoshop in order to make it "fit" onto the Openstreet base map.

Now I have a png file with the "correct" projection. My problem is that I now have to make tiles from this image which can be used as overlay and thus need to set the correct coordinates. I can find out the exact lat/lon values using OSM but how can I tell gdal2tiles where the top-left or bottom-right position of my image is?

My command line so far is:

$gdal2tiles.py -p 'raster' myimage.png

What I am missing is an idea on how to set coordinates. Do I have to use another tool prior to tile-making?

1

You can use QGIS for georeferencing (tutorial), then generate tiles with it (another tutorial). Finally, you should specify layer bounds in Leaflet tile layer with bounds option.

0

If your image uses paletted colours, you have to translate it first to RGB colours:

gdal_translate -expand rgb src_dataset dst_dataset

If your image is not placed correctly when loading into QGIS, use gdal_translate -a_ullr to set the bounds.

Since Openstreetmap uses EPSG:3857, you can directly reproject your image to that projection with

gdalwarp -s_srs ... -t_srs EPSG:3857 surcefile destinationfile

before tiling the destinationfile.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.