I have a 6 channel proprietary camera and I need to create a NDVI map. I created a map from each band, so now I have 6 files each one on a different band width.

How can I proceed now using QGIS?

  • Welcome to GIS StackExchange! What wavelengths does you camera capture? What are the wavelengths per channel? – R.K. Dec 26 '14 at 14:09

To create a NDVI image you need to use the channels for red and near infrared (NIR) reflectance. The red channel is usually in a wavelength range between 0.6-0.7µm and the near infrared channel in a range between 0.7-1.10µm. So if one of your 6 files is in one of these widths you can use it for the calculation.

In QGIS there are two ways to calculate the NDVI:

  1. Use the 'raster calculator'
  2. Use the 'radiometric indices' tool (orfeo toolbox)

--> 1. For the raster calculator way you need to know the NDVI equation: NDVI=(NIR-RED)/(NIR+RED). If you loaded your red and your NIR band file into QGIS they will appear in the 'raster band' content table in the raster calculator. When you chose one band file it will appear in the 'raster calculation expression' field. Use the 'operators' to express the equation. But be careful with the brackets! Following define the output file and go!

--> 2. Within the radiometric indices you don't need to write any equation but this tool can only work with layer stacked files. So you need to create a layer stack that contains all of your 6 bands first. You can do this with the 'merge' tool (raster-->miscellaneus-->merge). Take care that you enable 'layer stack'. The radiometric indices tool is part of the Orfeo Toolbox (OTB) that is part of the Processing framework. Hence OTB have to be installed and the Processing framework have to be configured properly (see --> http://docs.qgis.org/2.6/en/docs/user_manual/processing/3rdParty.html). When you open the Processing Toolbox go to OTB-->Feature Extraction-->Radiometric Indices. The input image is your layer stacked image. Now you have to define the red and the NIR band regarding to your layer stack. Then just choose NDVI at 'available radiometric indices' and go! You also have the opportunity to calculate other vegetation indices - just have a look at the 'help' tab or at http://www.orfeo-toolbox.org/SoftwareGuide/SoftwareGuidech12.html#x38-2060011.

  • Thank you JakobT. But I have a problem on each of the options you gave me. After merging the images, on the OTB parameters there are only 5 channels, and I have 6; after that when I process the following text appears on LOG, "Algorithm Radiometric Indices starting... unsupported operand type(s) for +: 'NoneType' and 'str' Vea el registro para más detalles". Then when I try to use the raster calculator the outcome is blank. I´ll keep trying. – Santiago Escobar Dec 29 '14 at 1:11
  • What wavelength range do you have for each channel? And what was your exact expression in the raster calculator? – JakobT Dec 29 '14 at 19:14
  • Hi, sorry but I´ve been away for some time. The images I have are on 450, 550, 650, 720, 750 and 850nm. – Santiago Escobar Jan 12 '15 at 23:22
  • I upload for Red and NIR images. Then on Raster Calculator it shows 3 channels per image, so there I get lost. And with the OTB, now it tells me that "OTB folder is not configured. Please configure it before running OTB algorithms", and I´m not good at all with configuring softwares and I can´t manage to do it. Thanks for bearing with me... – Santiago Escobar Jan 12 '15 at 23:35

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