dem无效值处修改编码，凑成海拔0

bin/dem2terrain.js

@@ -5,7 +5,7 @@ const path = require('path');
 const version = require('../package.json').version;
 
 // node版本检查
-if(+process.version.substring(1,3)<16){
+if (+process.version.substring(1, 3) < 16) {
   console.error(`node版本>=16，当前版本 ${process.version}`);
   process.exit();
 }
@@ -27,28 +27,32 @@ program
   .option('-g, --epsg <number>', '<可选> Tile适用坐标系，3857 | 4490 | 4326', 3857)
   .option('-c, --clean <number>', '<可选> 是否清空输出目录，0 | 1', 0)
   .option('-z, --zoom <number-number>', '<可选> 指定瓦片的等级生成范围。例如，想生成 7 ~ 12 级的瓦片，则输入 -z 7-12', '5-14')
-  .option('-e, --encoding <string>', '<可选> 指定瓦片的数据编码规则（mapbox 或 terrarium）', 'mapbox');
+  .option('-e, --encoding <string>', '<可选> 指定瓦片的数据编码规则（mapbox 或 terrarium）', 'mapbox')
+  .option('-b, --baseHeight <number>', '<可选> 基准高度，默认0', 0);
 
 // --- 解析参数
 program.parse();
 
 const options = program.opts();
 // 判别是否是配置文件还是命令行配置
 let params;
-if (options['configFile']) 
+if (options['configFile'])
   params = require(options['configFile']);
-else 
+else
   params = options;
 const inputDem = params['input'];
 const outputDir = params['output'];
-if(inputDem===undefined||outputDir===undefined){
+if (inputDem === undefined || outputDir === undefined) {
   console.log('参数缺失: 输入文件路径或输出目录必填');
   process.exit();
 }
 
 const encoding = params['encoding'];
 const epsg = Number(params['epsg']);
 const isClean = Number(params['clean']);
+let baseHeight = Number(params['baseHeight']);
+if (isNaN(baseHeight))
+  baseHeight = 0;
 let zoom = params['zoom'];
 zoom = zoom.split('-');
 const minZoom = Number(zoom[0]);
@@ -73,6 +77,7 @@ const logMsg = `\n>> 开始转换...
 - 瓦片编码: ${encoding === 'mapbox' ? 'mapbox(raster-dem)' : encoding}
 - 瓦片尺寸: 256 px
 - 瓦片等级: ${minZoom} 至 ${maxZoom} 级
+- 基准高度: ${baseHeight}
 `;
 console.log(logMsg);
 
@@ -81,5 +86,6 @@ main(inputDem, outputDir, {
   maxZoom,
   epsg,
   encoding,
-  isClean
+  isClean,
+  baseHeight
 });

package.json

@@ -1,6 +1,6 @@
 {
   "name": "dem2terrain",
-  "version": "2.2.4",
+  "version": "2.2.5",
   "description": "使用 GDAL 制作 DEM 栅格的地形瓦片",
   "main": "index.js",
   "preferGlobal": true,

src/createtile.js

@@ -4,7 +4,7 @@ const { mapboxEncode, terrariumEncode } = require('./dem-encode');
 const path = require('path');
 const fs = require('fs');
 
-let dataset = null, no_data = null, memDriver = null, pngDriver = null;
+let dataset = null, no_data = null, _baseHeight = 0, memDriver = null, pngDriver = null;
 function forEachHeightBuffer(heightBuffer, encode) {
     const channelLength = heightBuffer.length;
     const rBuffer = new Uint8Array(channelLength);
@@ -13,20 +13,15 @@ function forEachHeightBuffer(heightBuffer, encode) {
     const aBuffer = new Uint8Array(channelLength);
     for (let i = 0; i < channelLength; i++) {
         let heightVal = heightBuffer[i];
-        let color, alpha;
-        if (heightVal === no_data) {
-            color = [0, 0, 0];
-            alpha = 0;
-        }
-        else {
-            color = encode(heightVal);
-            alpha = 255;
-        }
-
+        let color;
+        if (heightVal === no_data)
+            color = [1, 134, 160]; // 编码后凑海拔=0，修复地形塌陷产生空白
+        else
+            color = encode(heightVal - _baseHeight);
         rBuffer[i] = color[0];
         gBuffer[i] = color[1];
         bBuffer[i] = color[2];
-        aBuffer[i] = alpha;
+        aBuffer[i] = 255;
     }
     return [rBuffer, gBuffer, bBuffer, aBuffer];
 }
@@ -67,11 +62,12 @@ function writeTerrainTile(overviewInfo, readinfo, writeinfo, encoding) {
 
 
 function createTile(createInfo, callback) {
-    const { outTileSize, overviewInfo, rb, wb, encoding, dsPath, x, y, z, outputTile } = createInfo;
+    const { outTileSize, overviewInfo, rb, wb, encoding, dsPath, x, y, z, outputTile, baseHeight } = createInfo;
     if (dataset === null) {
         dataset = gdal.open(dsPath, 'r');
         // 查询no_data数值
         no_data = dataset.bands.get(1).noDataValue;
+        _baseHeight = baseHeight;
     }
     // 创建一个mem内存，将读取的像素写入mem
     if (memDriver === null)

src/gdal-util.js

@@ -3,19 +3,19 @@ const gdal = require('gdal-async');
 function getBuildOverviewResampling(resampling) {
   switch (resampling) {
     case 1:
-      return "AVERAGE";
+      return "AVERAGE"; // 加权平均法
     case 2:
-      return "BILINEAR";
+      return "BILINEAR"; // 双线性内插法
     case 3:
-      return "CUBIC";
+      return "CUBIC"; // 三次卷积内插法
     case 4:
-      return "CUBICSPLINE";
+      return "CUBICSPLINE"; // B样条卷积内插法
     case 5:
-      return "LANCZOS";
+      return "LANCZOS"; // Lanczos窗口sinc卷积内插法
     case 6:
-      return "MODE";
+      return "MODE"; // 最常出现值法
     case 7:
-      return "NEAREST";
+      return "NEAREST"; // 最邻近法
     default:
       return "CUBIC";
   }

src/index.js

@@ -177,7 +177,7 @@ async function main(input, output, options) {
   // 计时开始
   const startTime = global.performance.now();
   // 结构可选参数
-  const { minZoom, maxZoom, epsg, encoding, isClean, resampling } = options;
+  const { minZoom, maxZoom, epsg, encoding, isClean, resampling, baseHeight } = options;
   // 固定瓦片尺寸
   const tileSize = 256;
   tileBoundTool = tileBoundMap.get(epsg);
@@ -190,19 +190,15 @@ async function main(input, output, options) {
     outputDir = path.join(os.tmpdir(), uuid());
 
   let stepIndex = 0;
-  //#region 步骤 1 - 高程值转 RGB，重新编码
   if (isClean === 1) {
     if (isSavaMbtiles === true && fs.existsSync(output))
       fs.unlinkSync(output);
     else
       emptyDir(output);
     console.log(`>> 步骤${++stepIndex}: 清空输出文件夹 - 完成`);
   }
-
-  //#endregion
   sourceDs = gdal.open(input, 'r');
   //#region 步骤 1 - 重投影
-
   if (sourceDs.srs.getAuthorityCode() !== epsg) {
     projectPath = project(sourceDs, epsg, resampling);
     projectDs = gdal.open(projectPath, 'r');
@@ -212,6 +208,7 @@ async function main(input, output, options) {
     projectDs = sourceDs;
   }
   sourceDs = null;
+  //#endregion
   //#region 步骤 2 - 建立影像金字塔 由于地形通常是30m 90m精度
   const overViewInfo = buildPyramid(projectDs, minZoom, resampling);
   console.log(`>> 步骤${++stepIndex}: 构建影像金字塔索引 - 完成`);
@@ -308,7 +305,8 @@ async function main(input, output, options) {
           x: j,
           y: i,
           z: tz,
-          outputTile: outputDir
+          outputTile: outputDir,
+          baseHeight
         };
         pileUpCount++;
         if (pileUpCount > 500)

test/app.js

@@ -1,18 +1,19 @@
 const path = require('path');
 const fs = require('fs');
 
-const demPath = path.join(__dirname, 'no_data.tif');
+const demPath = path.join(__dirname, 'DEM.tif');
 const tileDirPath = path.join(__dirname, 'terrain');
 
 const config = {
-    "zoom": "5-13",
+    "zoom": "5-10",
     "epsg": 3857,
     "size": 256,
     "resampling": 3,
     "encoding": "mapbox",
     "input": demPath,
     "output": tileDirPath,
-    "clean": true
+    "clean": true,
+    "baseHeight":2100,
 }
 
 fs.writeFileSync(path.join(__dirname, 'config.json'), JSON.stringify(config));

test/terrain_mapbox.html

@@ -26,7 +26,7 @@
   <div id="map"></div>
   <script>
     // 注意，请写自己的token运行
-    mapboxgl.accessToken = '';
+    mapboxgl.accessToken = 'pk.eyJ1IjoiYm9ibzlvayIsImEiOiJja3cxZjU1Z2UwMnFnMzBvajh4Y29iZTBiIn0.NcOkYbGRCj-C-gm1my6NZg';
 
     const map = new mapboxgl.Map({
       container: 'map',