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I'm trying for some time to convert a weather radar map (gnomonical projection) to mercator (EPSG_3395) and then layout it onto third-party web map so far unsuccessfully.

The original image: Raw picture

The projection can be defined by: +proj=gnom +lat_0=50.008 +lon_0=14.447 +x_0=0 +y_0=0

I can convert pixel coordinates from origin of the projection with ratio 1:1000 by:

cs2cs +proj=gnom +lat_0=50.008 +lon_0=14.447 +to +init=epsg:4326 -f "%.9f"

which gives me those corner coordinates:

    -301500 +217500 top     left:  10.062746833 51.879564163
    +427500 -310500 bottom  right: 20.076498030 47.082819838

My next step is to add metadata to image:

gdal_translate -a_srs "+proj=gnom +lat_0=50.008 +lon_0=14.447" -a_ullr -301500 +217500 729000 528000
            infile.png translated.png

Finally when I try to reproject whole image by:

gdalwarp -overwrite -s_srs "+proj=gnom +lat_0=50.008 +lon_0=14.447" -t_srs EPSG:3395 translated.png warped.png

I get wrong result. I'm new to GDAL. Where am I wrong and how can I rewrite my commands to make the reprojection go well?

  • Tip: use gdalinfo to see data about your raster files including their location. – Spacedman Sep 9 at 22:03
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gdal_translate needs the coordinates of the corners - I don't know where your " 729000 528000" come from - I guess the width/height? No, it should be the coordinates:

 gdal_translate -a_srs "+proj=gnom +lat_0=50.008 +lon_0=14.447" -a_ullr -301500 +217500 427500 -310500 QQNDR.png located.tiff

Another change I've made is to name the output .tiff since its a TIFF file.

After reprojection it loads perfectly into QGIS in the right location:

gdalwarp -overwrite -s_srs "+proj=gnom +lat_0=50.008 +lon_0=14.447" -t_srs EPSG:3395 located.tiff warped.tiff

enter image description here

  • Thank you, I really assumed the third and the fourth parameter is width and height. Now everything goes well. – W. Smith Sep 10 at 8:41

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