How can i access raster calculator (to generate NDVI) in QGIS?
In case this is not a recommended method, is there any other way to generate NDVI in QGIS?
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2It would be very helpful if you tell us what you did so far, what errors occur, what dataset you intend to use and so on. Otherwise we can only give imprecise answers.– CurlewJun 25, 2014 at 7:29
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2 Answers
For Raster calculator see the attached image. I suppose you have a Red-Green-Blue-NIR image as input and NDVI is calculated as (NIR-Red)/(NIR+Red) as in reference http://en.wikipedia.org/wiki/Normalized_Difference_Vegetation_Index
Four-band NIR images have usually band order 1) natural red, 2) natural green, 3) natural blue, 4) near infrared. NDVI formula in this case is
(b4-b1) / (b4+b1)
Three-band color-infrared images use bands 1) near infrared, 2) natural red, 3) natural green and the formula would be
(b1-b2)/(b1+b2)
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can you tell me which image(source) to use and how to proceed further Jun 25, 2014 at 7:44
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Unfortunately I am not expert on this area but I suppose that any image which has bands for these two ranges: "chlorophyll, strongly absorbs visible light (from 0.4 to 0.7 µm) for use in photosynthesis. The cell structure of the leaves, on the other hand, strongly reflects near-infrared light (from 0.7 to 1.1 µm)" Jun 25, 2014 at 7:48
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could you give me the link of any image you know if possible. And do you have any idea what to do after getting the image, like do i need georeferencing or digitization, or go directly with the calculation. Jun 25, 2014 at 7:55
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I have no such images at hand and you are as good as I in using search engines. Search for "false-color infrared" or "color-infrared". If you find 3-band color-infrared images the band order, as I have understood is 1: NIR, 2: natural red, 3: natural green. The formula then would be (b1-b2)/(b1+b2). Jun 25, 2014 at 8:05
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you can take sample images of IKONOS from here satimagingcorp.com/satellite-sensors/ikonos they have 4 bands– dowiJun 25, 2014 at 8:33
with recent version, you can use the OTB built in functionnalities, which include RadiometricIndices or BandMath.