编辑：我相信我的问题是这个代码适用于整数缩放级别,但我希望它适用于浮动缩放级别.

我有一个iOS应用程序,用户可以在基于RouteMe的地图和基于MapKit的地图之间切换.

当他们切换源时,我希望能够在一个中显示完全相同的区域.但是,我无法弄清楚如何使它们匹配,因为RouteMe和MapKit使用不同的数据结构来描述地图边界.

这里有一些代码可以让它有点接近,但并不准确.此代码来自：http://troybrant.net/blog/2010/01/set-the-zoom-level-of-an-mkmapview/

我不确定这段代码是否应该修复,或者我可能忽略了一个更简单的解决方案.代码从列出的最后一个方法开始执行：

#define MERCATOR_OFFSET 268435456
#define MERCATOR_RADIUS 85445659.44705395

#pragma mark -
#pragma mark Map conversion methods

- (double)longitudetoPixelSpaceX:(double)longitude {
  return round(MERCATOR_OFFSET + MERCATOR_RADIUS * longitude * M_PI / 180.0);
}

- (double)latitudetoPixelSpaceY:(double)latitude {
  return round(MERCATOR_OFFSET - MERCATOR_RADIUS * logf((1 + sinf(latitude * M_PI / 180.0)) / (1 - sinf(latitude * M_PI / 180.0))) / 2.0);
}

- (double)pixelSpaceXToLongitude:(double)pixelX {
  return ((round(pixelX) - MERCATOR_OFFSET) / MERCATOR_RADIUS) * 180.0 / M_PI;
}

- (double)pixelSpaceYToLatitude:(double)pixelY {
  return (M_PI / 2.0 - 2.0 * atan(exp((round(pixelY) - MERCATOR_OFFSET) / MERCATOR_RADIUS))) * 180.0 / M_PI;
}


- (MKCoordinateSpan)coordinateSpanWithMapView:(MKMapView *)mapView
                             centerCoordinate:(CLLocationCoordinate2D)centerCoordinate
                                 andZoomLevel:(NSInteger)zoomLevel {
  // convert center coordiate to pixel space
  double centerPixelX = [self longitudetoPixelSpaceX:centerCoordinate.longitude];
  double centerPixelY = [self latitudetoPixelSpaceY:centerCoordinate.latitude];

  // determine the scale value from the zoom level
  NSInteger zoomExponent = 20 - zoomLevel;
  double zoomScale = pow(2,zoomExponent);

  // scale the map’s size in pixel space
  CGSize mapSizeInPixels = mapView.bounds.size;
  double scaledMapWidth = mapSizeInPixels.width * zoomScale;
  double scaledMapHeight = mapSizeInPixels.height * zoomScale;

  // figure out the position of the top-left pixel
  double topLeftPixelX = centerPixelX - (scaledMapWidth / 2);
  double topLeftPixelY = centerPixelY - (scaledMapHeight / 2);

  // find delta between left and right longitudes
  CLLocationdegrees minLng = [self pixelSpaceXToLongitude:topLeftPixelX];
  CLLocationdegrees maxLng = [self pixelSpaceXToLongitude:topLeftPixelX + scaledMapWidth];
  CLLocationdegrees longitudeDelta = maxLng - minLng;

  // find delta between top and bottom latitudes
  CLLocationdegrees minLat = [self pixelSpaceYToLatitude:topLeftPixelY];
  CLLocationdegrees maxLat = [self pixelSpaceYToLatitude:topLeftPixelY + scaledMapHeight];
  CLLocationdegrees latitudeDelta = -1 * (maxLat - minLat);

  // create and return the lat/lng span
  MKCoordinateSpan span = MKCoordinateSpanMake(latitudeDelta,longitudeDelta);
  return span;
}


- (void)setCenterCoordinate:(CLLocationCoordinate2D)centerCoordinate
                    zoomLevel:(NSUInteger)zoomLevel
                     animated:(BOOL)animated {

  // use the zoom level to compute the region
  MKCoordinateSpan span = [self coordinateSpanWithMapView:self       
                               centerCoordinate:centerCoordinate
                                   andZoomLevel:zoomLevel];
  MKCoordinateRegion region = MKCoordinateRegionMake(centerCoordinate,span);

  // set the region like normal
  [self setRegion:region animated:animated];
}

不幸的是,这是 Google Maps API的限制,它只在设置地图的缩放级别时接受整数值：当你设置MKMapView的显示区域时,Apple的MapKit代码调用底层的Google Maps API,结果 – 无论你使用哪种MapKit方法设置区域 – 是一个缩小到最接近的整数缩放级别的地图.

Troy Brant的代码将带您完整的循环,并在MapKit API上方放置一个图层,允许您直接设置缩放级别…但最终您无法精确控制MKMapView显示的区域,除非您想要的缩放级别map恰好是一个整数.

Stack Overflow上出现了这个问题的几个变种(例如,MKMapView setRegion “snaps” to predefined zoom levels?和MKMapView show incorrectly saved region),但到目前为止还没有人想出一种编程方式来制作具有非整数缩放级别的地图,我怀疑它需要合作谷歌与苹果之间的关系永远让它成真.

我在 android位图缩放和采样之间有困惑这里可能有两个代码用于缩放,另一个用于采样任何人都可以帮助我识别这两个代码的工作以及它们之间的主要区别.

缩放：

public static Bitmap getScaleBitmap(Bitmap bitmap,int newWidth,int newHeight) {
    int width = bitmap.getWidth();
    int height = bitmap.getHeight();
    float scaleWidth = ((float) newWidth) / width;
    float scaleHeight = ((float) newHeight) / height;

    Matrix matrix = new Matrix();
    matrix.postScale(scaleWidth,scaleHeight);
    return Bitmap.createBitmap(bitmap,width,height,matrix,false);
}

抽样：

mImageView.setimageBitmap(decodeSampledBitmapFromresource(getResources(),R.id.myimage,100,100));

public static Bitmap decodeSampledBitmapFromresource(Resources res,int resId,int reqWidth,int reqHeight) {

    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeResource(res,resId,options);

    options.inSampleSize = calculateInSampleSize(options,reqWidth,reqHeight);

    options.inJustDecodeBounds = false;
    return BitmapFactory.decodeResource(res,options);
}

public static int calculateInSampleSize(
            BitmapFactory.Options options,int reqHeight) {
    final int height = options.outHeight;
    final int width = options.outWidth;
    int inSampleSize = 1;

    if (height > reqHeight || width > reqWidth) {

        final int halfheight = height / 2;
        final int halfWidth = width / 2;

        while ((halfheight / inSampleSize) >= reqHeight
                && (halfWidth / inSampleSize) >= reqWidth) {
            inSampleSize *= 2;
        }
    }

    return inSampleSize;
}

这里两个代码执行图像调整大小但不同的方式,所以我如何识别哪一个是好的和简单的.

缩放：首先,您在内存中解码整个位图,然后进行缩放.

采样：您可以获得所需的缩放位图,而无需在内存中加载整个位图.