我正在使用一个使用MKOverlay视图的应用程序,在Google基础地图上叠加自己的自定义地图.我一直在使用苹果的优秀的TileMap示例代码(来自WWDC 2010)作为指导.
我的问题 – 当“过度缩放”到比我生成的图块集更深的细节水平时,代码不显示,因为在计算的Z级别没有可用的图块.
我想要的行为 – 当“超缩”应用程序应该只是继续放大最深层次的瓷砖.这是一个很好的用户体验叠加层变得模糊 – 这是一个非常糟糕的体验,使覆盖消失.
这里是返回绘制图块的代码 – 我需要弄清楚如何修改它以覆盖Z深度,而不会破坏为叠加图块计算的帧的缩放.有什么想法吗？？？
- (NSArray *)tilesInMapRect:(MKMapRect)rect zoomScale:(MKZoomScale)scale
{
NSInteger z = zoomScaleToZoomLevel(scale);
// PROBLEM: I need to find a way to cap z at my maximum tile directory depth.
// Number of tiles wide or high (but not wide * high)
NSInteger tilesAtZ = pow(2,z);
NSInteger minX = floor((MKMapRectGetMinX(rect) * scale) / TILE_SIZE);
NSInteger maxX = floor((MKMapRectGetMaxX(rect) * scale) / TILE_SIZE);
NSInteger minY = floor((MKMapRectGetMinY(rect) * scale) / TILE_SIZE);
NSInteger maxY = floor((MKMapRectGetMaxY(rect) * scale) / TILE_SIZE);
NSMutableArray *tiles = nil;
for (NSInteger x = minX; x <= maxX; x++) {
for (NSInteger y = minY; y <= maxY; y++) {
// As in initWithTilePath,need to flip y index
// to match the gdal2tiles.py convention.
NSInteger flippedY = abs(y + 1 - tilesAtZ);
NSString *tileKey = [[NSString alloc]
initWithFormat:@"%d/%d/%d",z,x,flippedY];
if ([tilePaths containsObject:tileKey]) {
if (!tiles) {
tiles = [NSMutableArray array];
}
MKMapRect frame = MKMapRectMake((double)(x * TILE_SIZE) / scale,(double)(y * TILE_SIZE) / scale,TILE_SIZE / scale,TILE_SIZE / scale);
NSString *path = [[NSString alloc] initWithFormat:@"%@/%@.png",tileBase,tileKey];
ImageTile *tile = [[ImageTile alloc] initWithFrame:frame path:path];
[path release];
[tiles addObject:tile];
[tile release];
}
[tileKey release];
}
}
return tiles;
}
FYI,这里是有人问过的zoomScaleToZoomLevel帮助器函数：
// Convert an MKZoomScale to a zoom level where level 0 contains 4 256px square tiles,// which is the convention used by gdal2tiles.py.
static NSInteger zoomScaleToZoomLevel(MKZoomScale scale) {
double numTilesAt1_0 = MKMapSizeWorld.width / TILE_SIZE;
NSInteger zoomLevelAt1_0 = log2(numTilesAt1_0); // add 1 because the convention skips a virtual level with 1 tile.
NSInteger zoomLevel = MAX(0,zoomLevelAt1_0 + floor(log2f(scale) + 0.5));
return zoomLevel;
}
解决方法
想象一下,覆盖层是云覆盖 – 或者在我们的情况下,是蜂窝信号覆盖.在深度放大时可能不会“看起来很好”,但覆盖层仍然向用户传达必要的信息.
我已经解决了这个问题,添加了一个OverZoom模式来增强Apple的TileMap示例代码.
这是TileOverlay.m中的新TileInMapRect函数：
- (NSArray *)tilesInMapRect:(MKMapRect)rect zoomScale:(MKZoomScale)scale
{
NSInteger z = zoomScaleToZoomLevel(scale);
// OverZoom Mode - Detect when we are zoomed beyond the tile set.
NSInteger overZoom = 1;
NSInteger zoomCap = MAX_ZOOM; // A constant set to the max tile set depth.
if (z > zoomCap) {
// overZoom progression: 1,2,4,8,etc...
overZoom = pow(2,(z - zoomCap));
z = zoomCap;
}
// When we are zoomed in beyond the tile set,use the tiles
// from the maximum z-depth,but render them larger.
NSInteger adjustedTileSize = overZoom * TILE_SIZE;
// Number of tiles wide or high (but not wide * high)
NSInteger tilesAtZ = pow(2,z);
NSInteger minX = floor((MKMapRectGetMinX(rect) * scale) / adjustedTileSize);
NSInteger maxX = floor((MKMapRectGetMaxX(rect) * scale) / adjustedTileSize);
NSInteger minY = floor((MKMapRectGetMinY(rect) * scale) / adjustedTileSize);
NSInteger maxY = floor((MKMapRectGetMaxY(rect) * scale) / adjustedTileSize);
NSMutableArray *tiles = nil;
for (NSInteger x = minX; x <= maxX; x++) {
for (NSInteger y = minY; y <= maxY; y++) {
// As in initWithTilePath,need to flip y index to match the gdal2tiles.py convention.
NSInteger flippedY = abs(y + 1 - tilesAtZ);
NSString *tileKey = [[NSString alloc] initWithFormat:@"%d/%d/%d",flippedY];
if ([tilePaths containsObject:tileKey]) {
if (!tiles) {
tiles = [NSMutableArray array];
}
MKMapRect frame = MKMapRectMake((double)(x * adjustedTileSize) / scale,(double)(y * adjustedTileSize) / scale,adjustedTileSize / scale,adjustedTileSize / scale);
NSString *path = [[NSString alloc] initWithFormat:@"%@/%@.png",tileKey];
ImageTile *tile = [[ImageTile alloc] initWithFrame:frame path:path];
[path release];
[tiles addObject:tile];
[tile release];
}
[tileKey release];
}
}
return tiles;
}
这里是TileOverlayView.m中的新的drawMapRect：
- (void)drawMapRect:(MKMapRect)mapRect
zoomScale:(MKZoomScale)zoomScale
inContext:(CGContextRef)context
{
// OverZoom Mode - Detect when we are zoomed beyond the tile set.
NSInteger z = zoomScaleToZoomLevel(zoomScale);
NSInteger overZoom = 1;
NSInteger zoomCap = MAX_ZOOM;
if (z > zoomCap) {
// overZoom progression: 1,(z - zoomCap));
}
TileOverlay *tileOverlay = (TileOverlay *)self.overlay;
// Get the list of tile images from the model object for this mapRect. The
// list may be 1 or more images (but not 0 because canDrawMapRect would have
// returned NO in that case).
NSArray *tilesInRect = [tileOverlay tilesInMapRect:mapRect zoomScale:zoomScale];
CGContextSetAlpha(context,tileAlpha);
for (ImageTile *tile in tilesInRect) {
// For each image tile,draw it in its corresponding MKMapRect frame
CGRect rect = [self rectForMapRect:tile.frame];
UIImage *image = [[UIImage alloc] initWithContentsOfFile:tile.imagePath];
CGContextSaveGState(context);
CGContextTranslateCTM(context,CGRectGetMinX(rect),CGRectGetMinY(rect));
// OverZoom mode - 1 when using tiles as is,8 etc when overzoomed.
CGContextScaleCTM(context,overZoom/zoomScale,overZoom/zoomScale);
CGContextTranslateCTM(context,image.size.height);
CGContextScaleCTM(context,1,-1);
CGContextDrawImage(context,CGRectMake(0,image.size.width,image.size.height),[image CGImage]);
CGContextRestoreGState(context);
// Added release here because "Analyze" was reporting a potential leak. Bug in Apple's sample code?
[image release];
}
}
似乎现在工作很好
BTW – 我认为TileMap示例代码缺少一个[映像版本],并且正在泄漏内存.注意我在上面的代码中添加了它.
我希望这有助于其他一些同样的问题.
干杯,
>克里斯
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