How to draw Uber polyline?

问题

Uber app has a polyline that is curved, and even includes a shadow. The shadow may be just a black with transparent polyline connecting two points. That is easy. But the second polyline with curve, how to accomplish this? Is this a Bezier curve, or a built in function like setGeodesic(true)?

I have looked through the google maps examples and I see a section about circle polylines. Can this be adapted to create semi circles? Code snippet from demo.

PolylineOptions options = new PolylineOptions();
int radius = 5; //What is that?
int numPoints = 100;
double phase = 2 * Math.PI / numPoints;
for (int i = 0; i <= numPoints; i++) {
    options.add(new LatLng(SYDNEY.latitude + radius * Math.sin(i * phase),
            SYDNEY.longitude + radius * Math.cos(i * phase)));
}
int color = Color.RED;
mMap.addPolyline(options
        .color(color)
        .width(2));

回答1:

I was able to achieve this with the following bezier curve calculation

    double cLat = ((start.latitude + end.latitude) / 2);
    double cLon = ((start.longitude + end.longitude) / 2);

    //add skew and arcHeight to move the midPoint
    if(Math.abs(start.longitude - end.longitude) < 0.0001){
        cLon -= 0.0195;
    } else {
        cLat += 0.0195;
    }

    double tDelta = 1.0/50;
    for (double t = 0;  t <= 1.0; t+=tDelta) {
        double oneMinusT = (1.0-t);
        double t2 = Math.pow(t, 2);
        double lon = oneMinusT * oneMinusT * start.longitude
                + 2 * oneMinusT * t * cLon
                + t2 * end.longitude;
        double lat = oneMinusT * oneMinusT * start.latitude
                + 2 * oneMinusT * t * cLat
                + t2 * end.latitude;
        alLatLng.add(new LatLng(lat, lon));
    }

    // draw polyline
    PolylineOptions line = new PolylineOptions();
    line.width(POLYGON_STROKE_WIDTH_PX);
    line.color(Color.RED);
    line.addAll(alLatLng);
    map.addPolyline(line);

来源：https://stackoverflow.com/questions/43661843/how-to-draw-uber-polyline

标签

android

google-maps

polyline