oblique.yaml

cameras:
    perspective:
        type: perspective
        vanishing_point: [0, -500]
styles:
    stereo:
        lighting: false
        base: polygons
        shaders:
            defines:
                EARTH_RADIUS: 6378137.0 //radius of ellipsoid, WGS84
                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; }

                    float flip(float lat) {
                        if (lat > 0.) return mod(lat + 9455000., 18910000.) - 9455000.;
                        if (lat <= 0.) return mod(lat - 9455000., 18910000.) + 9455000.;
                    }

                    vec2 oblique(float lat, float lon) {
                        float coslat = cos(lat);
                        float coslon = cos(lon);
                        float k = 1. / (1. + coslat * coslon);
                        return vec2(k * coslon * sin(lat), k * sin(lon));
                    }


                position: |
                    // mercator position of the current vertex, u_map_position = center of screen,
                    // position.xy = vertex screen position in meters from the center of the screen
                    vec2 mercator = u_map_position.xy + position.xy;
                    //float lat = y2lat_m(flip(mercator.y + u_map_position.y));
                    //float lat = y2lat_m(mercator.y + u_map_position.y);
                    float lat = y2lat_m(mercator.y);
                    float lon = x2lon_m(mercator.x);

                    // Latitude_Of_Origin
                    float centerlat = y2lat_m(u_map_position.y);
                    // Central_Meridian
                    float centerlon = x2lon_m(u_map_position.x);

                    // position.xy = polar(lat, lon);
                    //position.xy = polar(lat, lon, centerlat, centerlon);
                    position.xy = oblique(deg2rad(lat), deg2rad(lon)) * EARTH_RADIUS;

    stereolines:
        base: lines
        mix: stereo
sources:
    osm:
        type: TopoJSONTiles
        url:  //vector.mapzen.com/osm/all/{z}/{x}/{y}.topojson?api_key=vector-tiles-_vxMzew
layers:
    earth:
        data: { source: osm }
        draw:
            stereolines:
                order: 1
                color: purple
                width: 3px
    water:
        data: { source: osm }
        draw:
            stereolines:
                order: 2
                color: pink
                width: 1px
    boundaries:
        data: { source: osm }
        draw:
            stereolines:
                order: 10
                color: cyan
                width: 10px