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I have calculated the NDVI image and overlain GPS coordinates for a pack of wild animals over the top.

I would like to calculate the average NDVI of all the GPS points, and then calculate the average for all of the random points that I have also put over the top. I would like to do this for the entire map, and Zonal Statistics does not seem to be helping.

2 Answers 2

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  1. For getting the NDVI values for the points use Point sampling tool plugin. This plugin generate new point layer (based on input layer) with additional attribute with values taken from raster data.

  2. Then calculate average.

Inside QGIS:

Use Basic statistics for numeric fields from processing toolbox (or menu Vector --> Analysis Tools). This function generates html file with several statistics for given attribute. You can also view the results in menu Processing --> Results Viewer...

or outside QGIS :

Export (right click on layer Save as...) layers as .csv file or copy-paste only their attribute tables with Copy selected rows to clipboard (need to do selection first). Then you can handle your data in some spreadsheet editor.

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  • Is there any way I can get the NDVI values next to the gps coordinates in the attribute table?
    – ALEX
    Mar 22, 2017 at 12:50
  • @ALEX at first, you have to create point layer from your table with coordinates (thought that you already done it :) ). Use Add Delimited Text Layer function for this - see Creating a link between QGIS and a spreadsheet
    – Oto Kaláb
    Mar 22, 2017 at 13:25
  • @ALEX if you mean point surroundings, you have to create buffers and than use zonal statistics
    – Oto Kaláb
    Mar 22, 2017 at 17:08
  • Thank you very much for all of your help so far. It is much appreciated. When I do use the Zonal Statistics plugin I can't see the results...where would I find them ?
    – ALEX
    Mar 22, 2017 at 17:47
  • It would append attribute table of buffer layer
    – Oto Kaláb
    Mar 22, 2017 at 18:28
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Try the following (using QGIS 3.16.9 Hanover): Go to menu "Raster" --> "Miscellaneous" --> "Raster information". For input layer, select your NDVI raster file. Tick the box "Read and display image statistics". Save the file in desired location. Click "Run". Once the process is completed, open the html file and look for mean value.

Hope this helps?

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