Openlayers 3 可以用鼠标从ol.source.raster获取像素值吗

基于ol3和mapbox global terrain中的海平面高度，我们进行了类似的设置，将高程值放入平铺中，并使用ol.source.raster进行设置

            var elevation = new ol.source.TileImage({
                url: penetrationUrls[this.designator.toLowerCase()],
                projection: newProj,// "EPSG:27700", 
                crossOrigin: 'anonymous',
                tileGrid: tilegrid
            });
            var raster = new ol.source.Raster({
                sources: [elevation],
                operation: penetrates
            });

现在-

1） 当鼠标悬停在上方查询像素值以显示高程的工具提示时，是否有任何明智的方法来显示该高程？

---

2） 如果想要查询线串或其他东西后面的高度，是否有一种聪明的方法可以重用已加载的平铺？

我们不渲染层，下面的代码就是我最终使用的代码。跳过了正在操作高程源的光栅图层

如果对此有所改进，我会在平铺缓存上添加一个LRU缓存，也许可以挂接到ols平铺缓存中

            var elevation = new ol.source.TileImage({
                url: options.template,
                projection: elevationGridProjection,
                crossOrigin: 'anonymous',
                tileGrid: tilegrid
            });

            let tiles: { [key: string]: HTMLImageElement } = {};
            elevation.on("tileloadend", (e) => {
                let coord = e.tile.getTileCoord();
                tiles[coord.join('-')] = e.tile.getImage();

            });

            this.map.on('pointermove', (evt) => {
                // When user was dragging map, then coordinates didn't change and there's
                // no need to continue
                if (evt.dragging) {
                    return;
                }



                let coordinate = ol.proj.transform(evt.coordinate, this.map.getView().getProjection(), elevationGridProjection);

                let tileCoord = tilegrid.getTileCoordForCoordAndResolution(coordinate, this.map.getView().getResolution());
                let key = tileCoord.join('-');
                if (key in tiles) {

                    let origin = tilegrid.getOrigin(tileCoord[0]);
                    let res = tilegrid.getResolution(tileCoord[0]);
                    let tileSize = tilegrid.getTileSize(tileCoord[0]);
                    let w = Math.floor(((coordinate[0] - origin[0]) / res) % (tileSize[0] | tileSize as number));
                    let h = Math.floor(((origin[1] - coordinate[1]) / res) % (tileSize[1] | tileSize as number));

                    var canvas = document.createElement("canvas");
                    canvas.width = tiles[key].width;
                    canvas.height = tiles[key].height;

                    // Copy the image contents to the canvas
                    var ctx = canvas.getContext("2d");
                    ctx.drawImage(tiles[key], 0, 0);

                    let img = ctx.getImageData(0, 0, canvas.width, canvas.height);
                    let imgData = img.data;
                    let index = (w + h * 256) * 4;
                    let pixel = [imgData[index + 0], imgData[index + 1], imgData[index + 2], imgData[index + 3]];
                    let height = (-10000 + ((pixel[0] * 256 * 256 + pixel[1] * 256 + pixel[2]) * 0.01))

                    console.log(`HEIGHT: ${height}, ${w},${h},${img.width}, ${img.height},${img.data.length} ,${index}, [${pixel.join(',')}]`);

                }

            });

---

我们不渲染层，下面的代码就是我最终使用的代码。跳过了正在操作高程源的光栅图层

如果对此有所改进，我会在平铺缓存上添加一个LRU缓存，也许可以挂接到ols平铺缓存中

            var elevation = new ol.source.TileImage({
                url: options.template,
                projection: elevationGridProjection,
                crossOrigin: 'anonymous',
                tileGrid: tilegrid
            });

            let tiles: { [key: string]: HTMLImageElement } = {};
            elevation.on("tileloadend", (e) => {
                let coord = e.tile.getTileCoord();
                tiles[coord.join('-')] = e.tile.getImage();

            });

            this.map.on('pointermove', (evt) => {
                // When user was dragging map, then coordinates didn't change and there's
                // no need to continue
                if (evt.dragging) {
                    return;
                }



                let coordinate = ol.proj.transform(evt.coordinate, this.map.getView().getProjection(), elevationGridProjection);

                let tileCoord = tilegrid.getTileCoordForCoordAndResolution(coordinate, this.map.getView().getResolution());
                let key = tileCoord.join('-');
                if (key in tiles) {

                    let origin = tilegrid.getOrigin(tileCoord[0]);
                    let res = tilegrid.getResolution(tileCoord[0]);
                    let tileSize = tilegrid.getTileSize(tileCoord[0]);
                    let w = Math.floor(((coordinate[0] - origin[0]) / res) % (tileSize[0] | tileSize as number));
                    let h = Math.floor(((origin[1] - coordinate[1]) / res) % (tileSize[1] | tileSize as number));

                    var canvas = document.createElement("canvas");
                    canvas.width = tiles[key].width;
                    canvas.height = tiles[key].height;

                    // Copy the image contents to the canvas
                    var ctx = canvas.getContext("2d");
                    ctx.drawImage(tiles[key], 0, 0);

                    let img = ctx.getImageData(0, 0, canvas.width, canvas.height);
                    let imgData = img.data;
                    let index = (w + h * 256) * 4;
                    let pixel = [imgData[index + 0], imgData[index + 1], imgData[index + 2], imgData[index + 3]];
                    let height = (-10000 + ((pixel[0] * 256 * 256 + pixel[1] * 256 + pixel[2]) * 0.01))

                    console.log(`HEIGHT: ${height}, ${w},${h},${img.width}, ${img.height},${img.data.length} ,${index}, [${pixel.join(',')}]`);

                }

            });

---

如果还将光栅源中的内容渲染为图层，则有一种更容易获取像素数据的方法-使用

Map\forEachLayerAtPixel

。大概是这样的：

map.on('pointermove', function(evt) {
  map.forEachLayerAtPixel(evt.pixel, function(layer, pixel) {
    let height = (-10000 + ((pixel[0] * 256 * 256 + pixel[1] * 256 + pixel[2]) * 0.01));
    console.log(height);
  }, undefined, function(layer) {
    return layer.getSource() == raster;
  });
});

---

如果还将光栅源中的内容渲染为图层，则有一种更容易获取像素数据的方法-使用

Map\forEachLayerAtPixel

。大概是这样的：

map.on('pointermove', function(evt) {
  map.forEachLayerAtPixel(evt.pixel, function(layer, pixel) {
    let height = (-10000 + ((pixel[0] * 256 * 256 + pixel[1] * 256 + pixel[2]) * 0.01));
    console.log(height);
  }, undefined, function(layer) {
    return layer.getSource() == raster;
  });
});

---

谢谢：）我不知道像素。我想我们可以把立面图层添加到地图上并隐藏起来。我用一种更详细的解决方案更新了我的答案，这种解决方案允许更多的自由，但可能会改用这种方法。当你不使用该源渲染层时，这种方法不起作用，并且该层也可能不会被隐藏。这也是我理解你答案的原因——我最终使用了作为答案发布的示例。考虑把它打包成可重复使用的东西。谢谢：）我不知道像素。我想我们可以把立面图层添加到地图上并隐藏起来。我用一种更详细的解决方案更新了我的答案，这种解决方案允许更多的自由，但可能会改用这种方法。当你不使用该源渲染层时，这种方法不起作用，并且该层也可能不会被隐藏。这也是我理解你答案的原因——我最终使用了作为答案发布的示例。考虑把它打包成可重用的东西。