Merge pull request #58 from geo-engine/bandwise-expression

bandwise expression

src/SUMMARY.md

@@ -33,6 +33,7 @@
 
 - [Operators](./operators/intro.md)
 
+  - [BandwiseExpression](./operators/bandwise-expression.md)
   - [ColumnRangeFilter](./operators/columnrangefilter.md)
   - [Expression](./operators/expression.md)
   - [GdalSource](./operators/gdalsource.md)

src/operators/bandwise-expression.md

@@ -0,0 +1,61 @@
+# Bandwise Raster Expression
+
+The `BandwiseExpression` operator performs a pixel-wise mathematical expression on each band of a raster source.
+For more details on the expression syntax, see the [Expression](/operators/expressions.md) operator.
+Note, that in the `BandwiseExpression` operator, it is only possible to map one pixel value to another and not reference any other pixels or bands.
+The variable name for the pixel value is `x`.
+
+## Parameters
+
+| Parameter    | Type                                             | Description                                                                                                 | Example Value                   |
+| ------------ | ------------------------------------------------ | ----------------------------------------------------------------------------------------------------------- | ------------------------------- |
+| `expression` | `Expression`                                     | Expression script                                                                                           | <pre><code>ln(1/x)</code></pre> |
+| `outputType` | [`RasterDataType`](/datatypes/rasterdatatype.md) | A raster data type for the output                                                                           | <pre><code>U8</code></pre>      |
+| `mapNoData`  | `bool`                                           | Should NO DATA values be mapped with the `expression`? Otherwise, they are mapped automatically to NO DATA. | <pre><code>false</code></pre>   |
+
+## Inputs
+
+The `Expression` operator expects a single raster input .
+
+| Parameter | Type                 |
+| --------- | -------------------- |
+| `source`  | `SingleRasterSource` |
+
+## Errors
+
+The parsing of the expression can fail if there are, e.g., syntax errors.
+
+## Example JSON
+
+```json
+{
+  "type": "BandwiseExpression",
+  "params": {
+    "expression": "ln(1/x)",
+    "outputType": "F32",
+    "mapNoData": false
+  },
+  "sources": {
+    "raster": {
+      "type": "RasterStacker",
+      "params": {},
+      "sources": {
+        "rasters": [
+          {
+            "type": "GdalSource",
+            "params": {
+              "data": "sentinel2-b8"
+            }
+          },
+          {
+            "type": "GdalSource",
+            "params": {
+              "data": "sentinel2-b4"
+            }
+          }
+        ]
+      }
+    }
+  }
+}
+```

src/operators/expression.md

@@ -87,7 +87,7 @@ However, the last expression must be without a semicolon.
 
 ## Inputs
 
-The `Expression` operator expects one rater input with at most 8 bands.
+The `Expression` operator expects one raster input with at most 8 bands.
 
 | Parameter | Type                 |
 | --------- | -------------------- |