Remove multi-source restrictions and fix alpha

examples/cog-math-multisource.html

@@ -6,7 +6,8 @@ docs: >
   The GeoTIFF layer in this example calculates the Normalized Difference Vegetation Index (NDVI)
   and Normalized Difference Water Index (NDWI) from two cloud-optimized Sentinel 2 GeoTIFFs: one
   with 10 m resolution and red and a near infrared bands, and one with 60 m resolution and a short
-  wave infrared channel. The NDVI is shown as green, the NDWI as blue.
+  wave infrared channel. The NDVI is shown as green, the NDWI as blue. The 4th band is the alpha
+  band, which gets added when a source has a `nodata` value configured.
 tags: "cog, ndvi, ndwi, sentinel, geotiff"
 ---
 <div id="map" class="map"></div>

examples/cog-math-multisource.js

@@ -7,17 +7,16 @@ const source = new GeoTIFF({
   sources: [
     {
       url: 'https://s2downloads.eox.at/demo/Sentinel-2/3857/R10m.tif',
-      samples: [2],
+      bands: [2, 3],
-      max: 65535,
+      min: 0,
-    },
+      nodata: 0,
-    {
-      url: 'https://s2downloads.eox.at/demo/Sentinel-2/3857/R10m.tif',
-      samples: [3],
       max: 65535,
     },
     {
       url: 'https://s2downloads.eox.at/demo/Sentinel-2/3857/R60m.tif',
-      samples: [8],
+      bands: [8],
+      min: 0,
+      nodata: 0,
       max: 65535,
     },
   ],
@@ -51,6 +50,8 @@ const map = new Map({
           ['*', 255, ndvi],
           // blue: NDWI
           ['*', 255, ndwi],
+          // alpha
+          ['band', 4],
         ],
       },
       source,

src/ol/source/GeoTIFF.js

@@ -18,9 +18,10 @@ import {toSize} from '../size.js';
  * the configured min and max.
  * @property {number} [max] The maximum source data value.  Rendered values are scaled from 0 to 1 based on
  * the configured min and max.
- * @property {number} [nodata] Values to discard.
+ * @property {number} [nodata] Values to discard. When provided, an additional band (alpha) will be added
- * @property {Array<number>} [samples] Indices of the samples to be read from. If not provided, all samples
+ * to the data.
- * will be read.
+ * @property {Array<number>} [bands] Indices of the bands to be read from. If not provided, all bands will
+ * be read.
  */
 
 let workerPool;
@@ -179,7 +180,7 @@ class GeoTIFFSource extends DataTile {
     this.resolutionFactors_ = new Array(numSources);
 
     /**
-     * @type {number}
+     * @type {Array<number>}
      * @private
      */
     this.samplesPerPixel_;
@@ -239,7 +240,7 @@ class GeoTIFFSource extends DataTile {
     let origin;
     let tileSizes;
     let resolutions;
-    let samplesPerPixel;
+    const samplesPerPixel = new Array(sources.length);
     let minZoom = 0;
 
     const sourceCount = sources.length;
@@ -254,16 +255,10 @@ class GeoTIFFSource extends DataTile {
 
       for (let imageIndex = 0; imageIndex < imageCount; ++imageIndex) {
         const image = images[imageIndex];
-        const wantedSamples = this.sourceInfo_[sourceIndex].samples;
+        const wantedSamples = this.sourceInfo_[sourceIndex].bands;
-        const imageSamplesPerPixel = wantedSamples
+        samplesPerPixel[sourceIndex] = wantedSamples
           ? wantedSamples.length
           : image.getSamplesPerPixel();
-        if (!samplesPerPixel) {
-          samplesPerPixel = imageSamplesPerPixel;
-        } else {
-          const message = `Band count mismatch for source ${sourceIndex}, got ${imageSamplesPerPixel} but expected ${samplesPerPixel}`;
-          assertEqual(samplesPerPixel, imageSamplesPerPixel, 0, message);
-        }
         const level = imageCount - (imageIndex + 1);
 
         if (!sourceExtent) {
@@ -347,12 +342,6 @@ class GeoTIFFSource extends DataTile {
       }
     }
 
-    if (sourceCount > 1 && samplesPerPixel !== 1) {
-      throw new Error(
-        'Expected single band GeoTIFFs when using multiple sources'
-      );
-    }
-
     this.samplesPerPixel_ = samplesPerPixel;
     const sourceInfo = this.sourceInfo_;
     for (let sourceIndex = 0; sourceIndex < sourceCount; ++sourceIndex) {
@@ -361,15 +350,12 @@ class GeoTIFFSource extends DataTile {
         break;
       }
     }
-    let additionalBands = 0;
+    const additionalBands = this.addAlpha_ ? 1 : 0;
-    if (this.addAlpha_) {
+    this.bandCount =
-      if (sourceCount === 2 && samplesPerPixel === 1) {
+      samplesPerPixel.reduce((accumulator, value) => {
-        additionalBands = 2;
+        accumulator += value;
-      } else {
+        return accumulator;
-        additionalBands = 1;
+      }, 0) + additionalBands;
-      }
-    }
-    this.bandCount = samplesPerPixel * sourceCount + additionalBands;
 
     const tileGrid = new TileGrid({
       extent: extent,
@@ -408,7 +394,8 @@ class GeoTIFFSource extends DataTile {
         window: pixelBounds,
         width: size[0],
         height: size[1],
-        samples: source.samples,
+        samples: source.bands,
+        fillValue: source.nodata,
         pool: getWorkerPool(),
       });
     }
@@ -418,9 +405,9 @@ class GeoTIFFSource extends DataTile {
 
     return Promise.all(requests).then(function (sourceSamples) {
       const data = new Uint8ClampedArray(dataLength);
+      let dataIndex = 0;
       for (let pixelIndex = 0; pixelIndex < pixelCount; ++pixelIndex) {
         let transparent = addAlpha;
-        const sourceOffset = pixelIndex * bandCount;
         for (let sourceIndex = 0; sourceIndex < sourceCount; ++sourceIndex) {
           const source = sourceInfo[sourceIndex];
           let min = source.min;
@@ -437,10 +424,9 @@ class GeoTIFFSource extends DataTile {
 
           const nodata = source.nodata;
 
-          const sampleOffset = sourceOffset + sourceIndex * samplesPerPixel;
           for (
             let sampleIndex = 0;
-            sampleIndex < samplesPerPixel;
+            sampleIndex < samplesPerPixel[sourceIndex];
             ++sampleIndex
           ) {
             const sourceValue =
@@ -448,18 +434,21 @@ class GeoTIFFSource extends DataTile {
 
             const value = gain * sourceValue + bias;
             if (!addAlpha) {
-              data[sampleOffset + sampleIndex] = value;
+              data[dataIndex] = value;
             } else {
               if (sourceValue !== nodata) {
                 transparent = false;
-                data[sampleOffset + sampleIndex] = value;
+                data[dataIndex] = value;
               }
             }
+            dataIndex++;
           }
-
-          if (addAlpha && !transparent) {
-            data[sampleOffset + samplesPerPixel] = 255;
         }
+        if (addAlpha) {
+          if (!transparent) {
+            data[dataIndex] = 255;
+          }
+          dataIndex++;
         }
       }