Question

解决这个问题是我的解决方案：

修改：已更新，以反映抢劫案的答案。

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);
}

}

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()));

希望这有帮助。

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);
    }
}

Scott的答案中的问题是，circleRadius是使用一种方法计算的，该方法将米的值转换为像素的点数。但是，如果您想要的点不在赤道上，则半径将太小，因为转换不能说明经络在极点处聚集在一起的事实。但是，这可以通过乘以(1/ FloatMath.cos((float) Math.toRadians(mLat)))来纠正，这是我对斯科特原始答案所做的唯一更改。

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，画出的圆圈比原来的要小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）。

有些人可能觉得它很有用。

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);
    }
}

Answer 3

您要尝试显示的地理位置点（0.1275,51.507222）？这是在索马里沿海的某个地方。
super.draw(..)应该是draw()方法中的第一个语句。

Answer 4

在 onMapReady（）回调中添加以下代码。

Java

map.addCircle(new CircleOptions()
 .center(new LatLng(latitude, longitude))
 .radius(10000.0f)
 .strokeColor(Color.BLUE)
 .fillColor(Color.CYAN));

科特林

map.addCircle(CircleOptions()
 .center(LatLng(latitude, longitude))
 .radius(10000.0f)
 .strokeColor(Color.BLUE)
 .fillColor(Color.CYAN))

在Android MapView上绘制一个圆圈

4 个答案: