从ArrayList获取最近的点<LatLng>

Question

i'm working on a App that has a Google map and a Polyline to specify a route. What i want is that when the user opens the map it automatically put a marker on the nearest point between the user and the polyline.

I've already set up a function that gets the nearest point from the user to the polyline. If the distance is < 600 it puts a marker in that point. But what i want is to take all the Coordinates(of the polyline) that are < 600 meters from the user and choose the closest one... this is my code

polyline ArrayList:

 public ArrayList<LatLng> polylineList(){

    ArrayList<LatLng> coords = new ArrayList<LatLng>();

    coords.add(new LatLng(25.71687391423798,-100.3730825815284));
    coords.add(new LatLng(25.71682182829175,-100.3733097782636));
    coords.add(new LatLng(25.71678126641878,  -100.374090669652));
    coords.add(new LatLng(25.71683201122758, -100.3731781269444));
    coords.add(new LatLng(25.72018196813817, -100.3735084186905));
    coords.add(new LatLng(25.72031604576068,  -100.3736959395207));
    coords.add(new LatLng(25.71998332400039,   -100.3762802484946));
    coords.add(new LatLng(25.71994816609866,   -100.3764646004368));
    coords.add(new LatLng(25.72208094229626,   -100.3773901496331));
    coords.add(new LatLng(25.72139701948525, -100.3784182403878));
    coords.add(new LatLng(25.72088085424743, -100.3792655793197));
    coords.add(new LatLng(25.7211341509678, -100.3796660319109));
    coords.add(new LatLng(25.72119368137114,  -100.3807655073227));
    coords.add(new LatLng(25.72102639768713,  -100.3811907891904));
    coords.add(new LatLng(25.72079498457438,   -100.3810006195533));
    coords.add(new LatLng(25.720670392499,   -100.3799969462212));
    coords.add(new LatLng(25.72062014771428, -100.3798718252661));
    coords.add(new LatLng(25.71970136267208,  -100.3812225396649));
    coords.add(new LatLng(25.71935874972525,   -100.3814558417726));
    coords.add(new LatLng(25.71758071083912,    -100.3839700351668));
    coords.add(new LatLng(25.71722347802044,   -100.3838886540422));
    coords.add(new LatLng(25.71531766471047,    -100.3815788239292));
    coords.add(new LatLng(25.71564916096481,    -100.3804237189767));
    coords.add(new LatLng(25.7159267510913,   -100.3800793191019));
    coords.add(new LatLng(25.71627234185268,   -100.3795543063391));
    coords.add( new LatLng(25.71665021282444,    -100.3790150094068));

return coords; }

Then, i get the user's location and evaluate the coordinates with every ArrayList Index using the HAVERSINE formula, if the distace is <600 it will draw a marker.

 for (int i = 0; i < polylineList().size(); i++) {
                    Double latit = polylineList.get(i).latitude;
                    Double longit = polylineList.get(i).longitude;
                    LatLng newLatLng = new LatLng(latit, longit);
                    Double distance = distanceHaversine(userlatit, latit, userlongit, longit);
                    if (distance < 600) {
                        drawMarker(newLatLng);
                    }
                }

this is working correctly but it draws a lot of markers in the coordinates that are < 600 meters from the user's location. What i want is to draw a marker only in the nearest point of the polyline. Some sort of evaluate all the coords that are < 600 from the user and then choose the closest. Appreciate any help.

Answer 1

find minimum distance from user to available points, get the latlng associated with min distance and draw marker using that

private int minDistance = 0;
    private LatLng closestLatLng = null;
     for (int i = 0; i < polylineList().size(); i++) {
                        Double latit = polylineList.get(i).latitude;
                        Double longit = polylineList.get(i).longitude;
                        LatLng newLatLng = new LatLng(latit, longit);
                        Double distance = distanceHaversine(userlatit, latit, userlongit, longit);
                        if (distance < minDistance) {
                            closestLatLng = newLatLng;
                            minDistance = distance;
                        }
                    }
    if(closestLatLng !=null && minDistance < 600){
        drawMarker(closestLatLng);
    }

Answer 2

There is Map Utils class for map by using that you can find location that is at particular distance from your current location on polyline

if (PolyUtil.isLocationOnPath(start, points, true, 10)) {
      // do your stuf here
}

here start is your current location, points is array of polyline points and last parameter is for range(distance) from your path in meter.

for this you have to add this dependancy into your gradle.

compile 'com.google.maps.android:android-maps-utils:0.5+'

hope this helps you.