Revision as of 15:51, 20 June 2019

Vegetation index using the Raster Calculator

Click the Open Data Source Manager and then Add raster layer and select the file /geodata_lab01/raster/s2/Subset_S2A_MSIL2A_20170619T_MUL.tif.
Check the rank and spectral range of bands in the multiband file (e.g. see table Changing Raster Layer Style).
After clicking Open, the raster layer appears in the QGIS canvas.
Click Raster --> Raster calculator.
A powerful normalization is realized by the normalized difference vegetation index that forms the basis of most vegetation indices $NDVI = (Nir - Red) / (Nir + Red)$. It can be implemented using Raster Calculator as seen in the following screenshot:

Define path and file name of the output layer. OK.
Map visualization: Open the raster layer properties by right-clicking the ndvi raster in the TOC selecting Properties, or by simply double clicking.
Select the Style tab. Under Render type select Singleband pseudocolor.
- Open the In the pulldown menu of Color ramp by clicking on Select All color ramps --> RdYlGn. In the Mode select Equal interval. Set the number of Classes to 10 and click Classify.
- To finish, click Apply (see Fig. A).

A convenient module for calculating one or several spectral indices at the same time can be found in the QGIS processing toolbox.

Type Radiometric into the search field and find the OTB --> Feature Extraction --> Radiometric Indices) tool.
Open it with a double click.
Assign the bands in the multiband file to the correct spectral sensitivity.
in the text field Available Radiometric Indices type:Vegetation:NDVI
Click Run.
Click Helpto find definitions of available spectral indices in three categories (vegetation, water, soil) and relevant channels of the input multiband image.

Figure A: False color composite RGB = 4,3,2	Figure B: Single band NDVI

@@ Line 19: / Line 19: @@
 * in the text field ''Available Radiometric Indices'' type:{{typed|text=Vegetation:NDVI}}
 * Click {{button|text=Run}}.
-* Click {{button|text=Help}}to find an overview on available spectral indices in three categories (vegetation, water, soil) and relevant channels of the input multiband image.
+* Click {{button|text=Help}}to find definitions of available spectral indices in three categories (vegetation, water, soil) and relevant channels of the input multiband image.
 [[File:Qgis_radio_index.png|left|400px]]
 * Display the output single band spectral index image in the canvas ('''Fig. B''').
 {| class="wikitable"
-| style="border: 0pt" | [[file:Qgis_ndvi_pseudo.png|thumb|left|400px|'''Figure A:''' Single band NDVI displayed with color table ''RdYlGn'']]
+| style="border: 0pt" | [[file:Qgis_ndvi_pseudo.png|thumb|left|400px|'''Figure A:''' False color composite ''RGB = 4,3,2'']]
-| style="border: 0pt" | [[file:Qgis_vi_composite.png|thumb|left|400px|'''Figure B:''' Color composite of three spectral indices: RGB=NDVI, BI2, NDWI]]
+| style="border: 0pt" | [[file:Qgis_vi_composite.png|thumb|left|400px|'''Figure B:''' Single band NDVI]]
 |}
 [[Category:Working with Raster Data]]