### How to use Landsat Images ( Free ) with QGis 2.8 for NDVI

In the previous two articles, we have discussed ( How
to use Landsat images (free) with ArcGIS (ArcMap) for NDVI
, How
to use Landsat images (free) with ArcGIS Pro for NDVI
) the calculation and
display of NDVI with ArcMap and ArcGis Pro. In this article we will
discuss how to achieve this
operation
with QGis.
To
this
article: How
to use Landsat Images ( Free ) in

Here we will use the raster calculator to calculate the NDVI
, then we will discuss how to create and use a specific colour

If you work with a Landsat 7 image,
you will load in QGis the bands 3 (red) and
4 (infra-red). If you work
with a Landsat 8 image you will load the bands 4 (red)
and 5 (infra-red).

To
open the raster calculator , click on the Raster-> Raster Calculator menu

We will return the formula

NDVI = PIR – R / PIR + R

Where PIR is
the near infrared band and R is the red band

In our example:

(“LE72020272014184ASN00_B4
@ 1″ – “LE72020272014184ASN00_B3 @ 1”) –
(“LE72020272014184ASN00_B4 @ 1” + “LE72020272014184ASN00_B3 @
1″)

The result displays as :

You can work
directly
using this result but it is
to refer to a standard symbology .
We
are used to represent NDVI in a complete scale from -1 to +1
( here the result expands from -0.5 to +0.506),
to represent the negative values, which do not correspond to vegetation , by a
gradient of blue, and the positive values , which correspond to vegetation , by
a gradient from green to red passing through the yellow .

is
not available in   QGis
as such.

To create it , open notepad and type the following text:

<? xml version = “1.0” encoding =
“UTF-8”?>

<svg xmlns =
“http://www.w3.org/2000/svg” version = “1.1” width =
“300px” height = “45px”
viewBox = “0 0
300 45″>

<g>
< defs >
= “pad” x1 = “0%” x2 = “100%” y1 =
“0%” y2 = “0%”>

<stop offset = “0.00%” stop- color
= “ rgb (0,0,255)” stop-opacity = “1.0000”
/>

<stop offset = “49.90%” stop- color
= “ rgb (190,210,255)” stop-opacity =
“1.0000” />

<stop offset = “50.00%” stop- color
= “ rgb (56,168,0)” stop-opacity =
“1.0000” />

<stop offset = “66.60%” stop- color
= “ rgb (255,255,0)” stop-opacity =
“1.0000” />

<stop offset = “100.00%” stop- color
= “ rgb (255,0,0)” stop-opacity = “1.0000”
/>

</ defs >
< rect fill = “ url (#NDVI)”
x = “4” y = “4” width = “292” height =
“37” stroke = “black” stroke-width = “1” />

</ g>
<creator name = “ nasca
version = “1.0” />

<created date = “Mon Mar 23 22:38:20 2015”
/>

</ svg>

Register
this
file
with the name NDVI.svg in the \ Program Files \
QGIS Wien \ apps \ qgis \ resources \
cpt -City-qgis-min \ cb
\ div

Now we are going apply this gradient to the resulting raster of the NDVI calculation: Double click on the legend of the raster to open the Properties window
In the Style tab , change the rendering type to “Pseudo colour single band”
Change the values from Min =-1 and from Max = 1.

In the drop down  list of colour palette, go to  the last line and click New color palette

In the Color Palette Type , select
-City cpt and
click
OK

The palette cpt -City opens

Open “Diverging” item and select cb/ div to find the ndvi palette that you have created .
Click on one of these, then click OK. Leave the default name and click OK
In Mode select equal intervals .
In Class select , for example , 20 .
Click the Sort button
You will see the scale to be applied to the raster.

Click
OK to close the properties layer window and see the final result :

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