Question: Creating NDVI images with PI no ir V2

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macmuzz asked on May 05, 2019 10:42
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So i am new to this and i have not been able to find a lot of info. this question has three parts. firstly i am using a PI No ir V2 camera with a blue filter to map a field. firstly i keep seeing things that say that it need to calibrate it. What am i calibrating and how? secondly secondly i want to take these photos and stitch them together to create a larger map that i can then process with NDVI. So what is the best software for processing NDVI ? i tried the inframgram.org one but i am looking for the one that shows green as healthy and red as not healthy. Can anyone help a noob out ?



4 Comments

These are really good questions.

1) Calibration - Calibration typically involves placing known reference samples in the scene, check out https://publiclab.org/tag/ndvi-calibrate, in particular @nedhorning

2) Image stitching- Image stitching can be done manually using Public lab’s Mapknitter https://mapknitter.org/ (you can stitch images even if they are not taken from above) or as
@cfastie noticed, the free Microsoft ICE(Windows only) will stitch photos into a single image and blend them together.

3) Processing NDVI- Another tool besides infragram is image sequencer , https://sequencer.publiclab.org/examples/#steps= . Image sequencer has more colormaps and histogram correction which also may prove useful.

You could also work processing direct on the Raspberry Pi . This is typically done with python applications. See @petter_mansson1 https://github.com/PiddePannkauga/ndviMachine code or my own code https://github.com/MargaretAN9/Peggy/blob/master/README.md (see examples at https://publiclab.org/profile/MaggPi )

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For calibrating the Raspberry PInoIR camera I wrote a gui application to just play around with till I found a good result. I looked for values that would look as close to a RGB picture as possible but depending on the filter used some colors would look of. The code can be found at https://github.com/PiddePannkauga/PiCameraGui. Run it on the raspberry pi. The image I have provided shows a good calibration in my opinion. This is using a blue filter that came with the PInoIR. The red gain for white balance is higher than the blue gain. All setups require different calibrations depending on how much light is present when capturing an image.

preNDVI_2019-3-29-10-20-5.png

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Where did you get the calibration objects shown in the picture? Do you know the exact spectral properties of the colored squares and that is how you are quantifying how accurate your white balance is?

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I just took some colored pieces of paper I found at the office. The paper squares was only added to show other people that I didnt just re color the image but actiaöly took images of different lightwaves than pne can be used to see from consumer cameras. I also did the calibration by using my gui application where I could manually set the properties of the camera.


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