google 地图的小知识点

google map的小知识点
1.Projection的作用
2.在Google Map上绘制直线的方法

绘制路线的步骤
1.确定路线的其实和终止的经纬度坐标；
2.在起点和终点上绘制图标；
3，将经纬度坐标换算成屏幕上的x轴/y轴
4，在起点和终点之间绘制路线；

Projection的作用
1.将地图上的经纬度坐标转化层层屏幕上的x轴和y轴的坐标
android.graphics.Point toPixels(GeoPoint in,android.graphics.Point out)
2.将x轴和y轴的坐标转换成地图上的经纬度坐标
GeoPoint fromPixels(int x,int y)

main.xml

<com.google.android.maps.MapView
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:enabled="true"
android:id="@+id/mapViewId"
android:apiKey=""
/>


//在MapView之上创建一个图层，需要创建一个类，实现Overlay，并生成该类的对象，然后将该队形加到MapView。getOverlay（）
//一个OverlayItem对象就代表了一个在地图上显示的标记
public class FirstOverlay extends ItemizedOverlay<OverlayItem>{
//创建一个List对象，用于持有该图层当中所有的标记对象
private ArrayList<OverlayItem> overlayItems = new ArrayList<OverlayItem>();
private Context context;

//第一个参数用于指定标记所使用的默认图片
public FirstOverlay(Drawable defaultMarker,Context context){
//必须调用父类的构造函数
supper(boundCenterBotton(defaultMarker));
this.context = context;
}

public FirstOverlay(Drawable defaultMarker){
supper(boundCenterBotton(defaultMarker));
}

//用于将生成好的OverlayItem对象添加到List当中
public void addOverlay(OverlayItem overlay){
overlayItems.add(overlay);
populate();
}

//用于创建一个overlayItem对象
@Override
protected OverlayItem createItem(int i){
return overlayItems.get(i);
}

//返回当前的overlay当中所报涵的overlayItem
@Override
public int size(){
return overlayItems.size();
}
//当用户点击标记时，所调用的函数
@Override
public boolean onTap(int index){
OverlayItem item = overlayItems.get(index);
AlterDialog.Builder builder = new AlterDialog.Builder(context);
builder.setTitle(item.getTitle());
builder.setMessage(item.getSnippet());
Dialog dialog = builder.create();
dialog.show();
return true;
}
}



public class MainActivity extends Activity {
    /** Called when the activity is first created. */
private Projection projection;
private List<Overlay> overlays;
private MapController mapContrroller;
private GeoPoint beginGeoPoint;
private GeoPoint endGeoPoint;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
       
        //指定起始和终止位置的经纬度
        beginGeoPoint = new GeoPoint(19240000, -99120000);
        endGeoPoint = new GeoPoint(19340000, -99220000);
       
        MapView mapView = (MapView) findViewById(R.id.mapViewId);
        mapView.setBuiltInZoomControls(true);
       
        //mapContrroller对象只要用于对地图进项控制
        mapContrroller = mapView.getController();
        overlays = mapView.getOverlays();
        projection = mapView.getProjection();
       
        overlays.add(new PointOverlay(beginGeoPoint));
        overlays.add(new PointOverlay(endGeoPoint));
        overlays.add(new LineOverlay(beginGeoPoint, endGeoPoint));
       
        //
        mapContrroller.animateTo(beginGeoPoint);
        mapContrroller.setZoom(12);
    }
   
   
    @Override
    protected boolean isRouteDisplayed(){
    return false;
    }
   
    //该类的对象用于在地图上绘制线条
    class LineOverlay extends Overlay {
    private GeoPoint begin;
    private GeoPoint end;
   
    public LineOverlay(){
   
    }
   
    public LineOverlay(GeoPoint begin, GeoPoint end){
    this.begin = begin;
    this.end = end;
    }
   
    public void draw(Canvas canvas,MapView mapv, boolean shadow){
    super.draw(canvas, mapv, shadow);
    Paint paint = new Paint();
    paint.setColor(Color.BLUE);
    paint.setStyle(Paint.Style.FILL_AND_STROKE);
    paint.setStrokeWidth(2);
    Point beginPoint = new Point();
    Point endPoint = new Point();
    Path path = new Path();
    projection.toPixels(beginGeoPoint,beginPoint);
    projection.toPixels(endGeoPoint,endPoint);
    path.moveTo(endPoint.x, endPoint.y);
    path.lineTo(beginPoint.x, beginPoint.y);
    canvas.drawPath(path, paint);
    }
    }
   
    //该类的对象的作用是在地图上绘制图标
    class PointOverlay extends Overlay{
    private GeoPoint geoPoint;
    public PointOverlay(){
   
    }
   
    public PointOverlay(GeoPoint geoPoint){
    this.geoPoint = geoPoint;
    }
   
    public void draw(Canvas canvas,MapView mapv, boolean shadow){
    super.draw(canvas, mapv, shadow);
    Point point = new Point(); 
    projection.toPixels(geoPoint, point);
    Bitmap bmp = BitmapFactory.decodeResource(getResources(), R.drawable.icon);
    Paint paint = new Paint();
    canvas.drawBitmap(bmp, point.x, point.y-20, paint);
    }
    }
}