[GIS] gdal2tiles generates small picture inside 256×256 tile

coordinate systemgdalgdal2tilesgeotiff-tifftiles

I've used gdal2tiles for generating tiles in number of different polar projections and always experienced the same problem — strange small picture inside normal 256×256 png with the rest of space transparent.
I'm using -p raster option.

That's how one particular tile looks like http://grab.by/uNHw

And here is the whole map view.

how whole map with such tile looks like

Looking for suggestions. Gladly will switch to other utility/program that can generate tiles properly in non-mercator projections.

Source geotiff I use are arctic and antarctic maps:

Sample command I use: gdal2tiles.py -z 3 -p raster ibcso_background_hq.tif

Best Answer

I'm not sure why, but gdal2tiles does not seem to like a combination of -z and -p raster.

So I used call gdal2tiles.bat -p raster ibcso_background_hq.tif

and got the right picture in all zoom levels:

enter image description here

Related Solutions

GDAL2Tiles – Calculate Lat Lon Bounds for Individual Tile

The math is described at:

http://www.maptiler.org/google-maps-coordinates-tile-bounds-projection/

…including the source code for command line utility and an online demonstration.

It is also pretty simple math:

function tile2long(x,z) { return (x/Math.pow(2,z)*360-180); }

function tile2lat(y,z) {
    var n=Math.PI-2*Math.PI*y/Math.pow(2,z);
    return (180/Math.PI*Math.atan(0.5*(Math.exp(n)-Math.exp(-n))));
}

Note the difference between XYZ/Google vs TMS in y axis.

Google Maps API V3 gives you the required functions too via .fromPointToLatLng() of map.getProjection().

[GIS] Raster Image Tiles created using GDAL2Tiles (from GDAL 2.4.2) does not align properly with Open Street Map Tile layer

You are trying to match two different map projections.

The default OpenStreetMap tiles use the EPSG:3857 coordinate reference system, AKA Web Mercator Projection. It looks like this:

On the other hand, the Natural Earth files use the EPSG:4326 coordianate reference system, AKA equirectangular projection. It looks like this:

The issue of map projections, reference ellipsoids and how those combine to form coordinate reference systems is not trivial if you're new to the GIS field. If you're asking yourself "which is the best projection", the answer is "all of them" (each for a different purpose).

In your particular case, you want gdal2tiles to generate epsg:3857 "mercator" tiles from a epsg:4326 raster source, reprojecting the data during the process.

So, tell gdal2tiles that you want mercator tiles with...

-p mercator

...and tell that the source raster is in EPSG:4326 with...

-s epsg:4326

...and everything together should look like:

gdal2tiles.py -z 0-8 -p mercator -s epsg:4326 NE1_LR_LC.tif Natural

Remember to run gdal2tiles.py --help for more info about command-line parameters.

Best Answer

Related Solutions

GDAL2Tiles – Calculate Lat Lon Bounds for Individual Tile

[GIS] Raster Image Tiles created using GDAL2Tiles (from GDAL 2.4.2) does not align properly with Open Street Map Tile layer

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