# r.mapcalculator

I am using QGIS 2.18.25. I'm struggling to use r.mapcalc to calculate the ndvi for a workbook project. R.mapcalculator is shown on the workbook I'm using and seems simpler to use. Is there a plug-in to load this onto my version or a more user friendly GRASS tool in the version I'm using

• Could you give more details (formula used, workbook extract/links) ? – gisnside Dec 7 '18 at 13:28

You should have a look at i.vi - Calculates different types of vegetation indices

Installed via QGIS 2.18.25/ Osgeo4W installer and in the toolbox panel (here in french)

One the indices is NDVI

``````arvi: Atmospherically Resistant Vegetation Index
dvi: Difference Vegetation Index
evi: Enhanced Vegetation Index
evi2: Enhanced Vegetation Index 2
gvi: Green Vegetation Index
gari: Green Atmospherically Resistant Vegetation Index
gemi: Global Environmental Monitoring Index
ipvi: Infrared Percentage Vegetation Index
msavi: Modified Soil Adjusted Vegetation Index
msavi2: second Modified Soil Adjusted Vegetation Index
>> ndvi: Normalized Difference Vegetation Index
pvi: Perpendicular Vegetation Index
sr: Simple Ratio
vari: Visible Atmospherically Resistant Index
wdvi: Weighted Difference Vegetation Index
``````

NDVI: Normalized Difference Vegetation Index

``````ndvi( redchan, nirchan )

Satellite specific band numbers ([NIR, Red]):
MSS Bands        = [ 7,  5]
TM1-5,7 Bands    = [ 4,  3]
TM8 Bands        = [ 5,  4]
Sentinel-2 Bands = [ 8,  4]
AVHRR Bands      = [ 2,  1]
SPOT XS Bands    = [ 3,  2]
AVIRIS Bands     = [51, 29]
``````

Formula :

``````NDVI = (NIR - Red) / (NIR + Red)
``````

Calculation of NDVI with GRASS

The calculation of NDVI from the reflectance values is done as follows:

``````g.region raster=band.3 -p
i.vi red=band.3 nir=band.4
viname=ndvi output=ndvi r.univar -e ndvi
``````

For Sean, to check the Osgeo4W install parameters. It seems i have both grass -&7 install on my machine :

• Hi I'm using QGIS 2.18.25. The workbook is Discover QGIS by locate press. Tried looking at i.vi but it's not a GRASS tool in this version of QGIS – Sean Jarrett Dec 9 '18 at 9:00
• Maybe you need to install QGIS via the osgeo4W advanced installer. I have in in my version (i'll update a picture). You're sure you're looked in the toolbox panel ? – gisnside Dec 10 '18 at 10:10
• I did install via osgeo4W advanced installer. Not sure how I can add a screen print to show the GRASS toolbox? – Sean Jarrett Dec 14 '18 at 11:09
• I updated my answer so you can see what lines I ticked on the osgeo4W install – gisnside Dec 15 '18 at 9:48