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How to use the raster calculator in QGIS?
Open the QGIS project corresponding to this lesson and you will see that it contains several raster layers. Now open the toolbox and open the dialog corresponding to the raster calculator. The interface is different in recent versions. The dialog contains 2 parameters. The layers to use for the analysis.
How to run QGIS with no data values?
For non English users: use always ”.”, not ”,”. Click Run to run the algorithm. You will get a layer that has the same appearance of the input layer, but with different values. The input layer that we used has valid values in all its cells, so the last parameter has no effect at all.
How to calculate no data values in raster calculator?
Open the calculator dialog and select both layers of the project in the input layers field. Enter the following formula in the corresponding field: a refers to the accumulated flow layer (since it is the first one to appear in the list) and b refers to the DEM.
What does the output extent of QGIS do?
However, we did not do anything. QGIS takes care of this situation and automatically resamples input layers when needed. The output extent is the minimum covering extent calculated from the input layers, and the minimum cell size of their cellsizes.
Where do I find the raster bands in QGIS?
The Raster bands list contains all loaded raster layers that can be used. To add a raster to the raster calculator expression field, double click its name in the Fields list. You can then use the operators to construct calculation expressions, or you can just type them into the box.
How to calculate Dem in a raster calculator?
Select the DEM in the layers field and type a * 3.28084 in the formula field. For non English users: use always “.”, not “,”. Click Run to run the algorithm. You will get a layer that has the same appearance of the input layer, but with different values.
How to define output layer in raster calculator?
In the Result layer section, you will need to define an output layer. You can then define the extent of the calculation area based on an input raster layer, or based on X,Y coordinates and on columns and rows, to set the resolution of the output layer.
How to sum up pixel values in QGIS?
This will give you the mean pixel value and the raster size in pixels. You could also get this data from the Properties -> Metadata tab. Then it’s a question of arithmetic: mean value x (height in pixels x width in pixels). Nick.
How to calculate logarithm in the raster calculator?
Using the logarithm of that flow accumulation will yield a much more informative representation. We can calculate that using the raster calculator. Open the algorithm dialog again, select the accflow layer as the only input layer, and enter the following formula: log (a).