mercator-functions.yaml

styles:
    mercator-functions:
        shaders:
            defines:
                EARTH_RADIUS: 6378137.0
                PI: 3.14159265358979323846
                HALF_PI: 1.570796327
                QUARTER_PI: .785398163
                deg2rad(d): (d)*PI/180.0
                rad2deg(d): (d)*180.0/PI
            blocks:
                global: |
                    // http://wiki.openstreetmap.org/wiki/Mercator
                    float y2lat_m (float y) { return rad2deg(2.0*atan(exp((y/EARTH_RADIUS)))-HALF_PI); }
                    float x2lon_m (float x) { return rad2deg(x/EARTH_RADIUS); }

                    float lat2y_m (float lat) { return EARTH_RADIUS*log(tan(QUARTER_PI+ deg2rad(lat)/2.0)); }
                    float lon2x_m (float lon) { return deg2rad(lon)*EARTH_RADIUS; }