在Android MapView上画一个圆圈

Question

修复这里是我的解决方案:

编辑:更新以反映robguinness答案.

import com.google.android.maps.GeoPoint;
import com.google.android.maps.MapView;
import com.google.android.maps.Overlay;
import com.google.android.maps.Projection;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Point;

public class CircleOverlay extends Overlay {

Context context;
double mLat;
double mLon;
float mRadius;

public CircleOverlay(Context _context, double _lat, double _lon, float radius ) {
    context = _context;
    mLat = _lat;
    mLon = _lon;
    mRadius = radius;
}

public CircleOverlay(Context _context, double _lat, double _lon, float radius ) {
    context = _context;
    mLat = _lat;
    mLon = _lon;
    mRadius = radius;
}

public void draw(Canvas canvas, MapView mapView, boolean shadow) {
    super.draw(canvas, mapView, shadow); 

    if(shadow) return; // Ignore the shadow layer

    Projection projection = mapView.getProjection();

    Point pt = new Point();

    GeoPoint geo = new GeoPoint((int) (mLat *1e6), (int)(mLon * 1e6));

    projection.toPixels(geo ,pt);
    float circleRadius = projection.metersToEquatorPixels(mRadius) * (1/ FloatMath.cos((float) Math.toRadians(mLat)));

    Paint innerCirclePaint;

    innerCirclePaint = new Paint();
    innerCirclePaint.setColor(Color.BLUE);
    innerCirclePaint.setAlpha(25);
    innerCirclePaint.setAntiAlias(true);

    innerCirclePaint.setStyle(Paint.Style.FILL);

    canvas.drawCircle((float)pt.x, (float)pt.y, circleRadius, innerCirclePaint);
}

}

要"绘制",需要将其添加到地图叠加层

mMapView.getOverlays().add(new CircleOverlay(context, loc.getLatitude(),loc.getLongitude()));

希望这可以帮助.

Answer 1

接受的答案有错误.我试图纠正它,但我的编辑因某些奇怪的原因被拒绝了.无论如何,这是一个更正的答案:

import com.google.android.maps.GeoPoint;
import com.google.android.maps.MapView;
import com.google.android.maps.Overlay;
import com.google.android.maps.Projection;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Point;

public class CircleOverlay extends Overlay {

    Context context;
    double mLat;
    double mLon;
    float mRadius;

    public CircleOverlay(Context _context, double _lat, double _lon, float radius ) {
        context = _context;
        mLat = _lat;
        mLon = _lon;
        mRadius = radius;
    }

    public CircleOverlay(Context _context, double _lat, double _lon, float radius ) {
        context = _context;
        mLat = _lat;
        mLon = _lon;
        mRadius = radius;
    }

    public void draw(Canvas canvas, MapView mapView, boolean shadow) {
        super.draw(canvas, mapView, shadow); 

        if(shadow) return; // Ignore the shadow layer

        Projection projection = mapView.getProjection();

        Point pt = new Point();

        GeoPoint geo = new GeoPoint((int) (mLat *1e6), (int)(mLon * 1e6));

        projection.toPixels(geo ,pt);
        float circleRadius = projection.metersToEquatorPixels(mRadius) * (1/ FloatMath.cos((float) Math.toRadians(mLat)));

        Paint innerCirclePaint;

        innerCirclePaint = new Paint();
        innerCirclePaint.setColor(Color.BLUE);
        innerCirclePaint.setAlpha(25);
        innerCirclePaint.setAntiAlias(true);

        innerCirclePaint.setStyle(Paint.Style.FILL);

        canvas.drawCircle((float)pt.x, (float)pt.y, circleRadius, innerCirclePaint);
    }
}

斯科特答案中的问题是,circleRadius是使用一种方法计算的,该方法可以在赤道上将点从米转换为像素.但是,如果您想要的点不在赤道上,则半径将太小,因为转换不能解释经络在极点处聚集的事实.然而,这可以通过乘以来得到纠正,(1/ FloatMath.cos((float) Math.toRadians(mLat)))这是我对斯科特原始答案所做的唯一改变.

我希望这有助于某人,因为我发现问题的方法很艰难.我住在芬兰,在那里使用原始方法,画出的圆圈比原本要小2倍!

Answer 2

我已经采用了上面的示例并对其进行了扩展,以考虑需要使用地图缩放级别缩放的圆圈(即:相对于地面距离的圆圈).

有些人可能会发现它很有用.

import com.google.android.maps.GeoPoint;
import com.google.android.maps.MapView;
import com.google.android.maps.Overlay;
import com.google.android.maps.Projection;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Point;

public class CircleOverlay extends Overlay {

    Context context;
    double mLat;
    double mLon;
    float mRadius;

     public CircleOverlay(Context _context, double _lat, double _lon, float radius ) {
            context = _context;
            mLat = _lat;
            mLon = _lon;
            mRadius = radius;
     }

     public void draw(Canvas canvas, MapView mapView, boolean shadow) {
         super.draw(canvas, mapView, shadow); 

         if(shadow) return; // Ignore the shadow layer

         Projection projection = mapView.getProjection();

         Point pt = new Point();

         GeoPoint geo = new GeoPoint((int) (mLat *1e6), (int)(mLon * 1e6));

         projection.toPixels(geo ,pt);
         float circleRadius = projection.metersToEquatorPixels(mRadius) * (1/ FloatMath.cos((float) Math.toRadians(mLat)));

         Paint innerCirclePaint;

         innerCirclePaint = new Paint();
         innerCirclePaint.setColor(Color.BLUE);
         innerCirclePaint.setAlpha(25);
         innerCirclePaint.setAntiAlias(true);

         innerCirclePaint.setStyle(Paint.Style.FILL);

         canvas.drawCircle((float)pt.x, (float)pt.y, circleRadius, innerCirclePaint);
    }
}