ios – 计算在“覆盖”图层之外的“过度放大”时,在MapRect中显示的图块

前端之家收集整理的这篇文章主要介绍了ios – 计算在“覆盖”图层之外的“过度放大”时,在MapRect中显示的图块前端之家小编觉得挺不错的,现在分享给大家,也给大家做个参考。
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

原文链接:https://www.f2er.com/iOS/330667.html

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