Forum

Author Topic: Generating an Ortophoto to calculate NDVI  (Read 7830 times)

dionybell

  • Newbie
  • *
  • Posts: 1
    • View Profile
Generating an Ortophoto to calculate NDVI
« on: August 20, 2014, 03:37:25 AM »
Hello, I'm about to start working with Photoscan, NIR aerial images and a UAV to calculate NDVI for Agricultre. But I have so many doubts.

When I generate a Orthophoto with NIR Images, instead of a RGB I'm getting a NIRGB, where NIR replaces Red.

But the formula for calculating NDVI is NIR-R/NIR+R. So how do I get NIR and R in separate bands to make the calculation?

I've noticed that Photoscan generates a 4 band Orthophoto, is the NIR placed in Band 4? Or it's left empty. I have noticed on regular RGB mosaics that the band 4 is empty, so I thought maybe Photoscan extracts the NIR and place it on Band 4. That would solve my problem.

Thanks in advance, looking forward for an answer.

uavmap

  • Newbie
  • *
  • Posts: 2
    • View Profile
Re: Generating an Ortophoto to calculate NDVI
« Reply #1 on: August 20, 2014, 07:24:13 AM »
Seeing as you don't have a red band in your captured data you cannot use red in the calculation. The only way to do this would be to fly the area again with RGB and then combine the bands accordingly.

Normally I would just use the blue band for the NDVI calculation instead of the red.

So (in your case) you would just do :

Band1 - Band3 / Band1 + Band3

There are lots of articles on the net about using different bands etc. One I found useful is http://agribotix.com/blog/2014/6/10/misconceptions-about-uav-collected-ndvi-imagery-and-the-agribotix-experience-in-ground-truthing-these-images-for-agriculture

jbosorio

  • Newbie
  • *
  • Posts: 1
    • View Profile
Re: Generating an Ortophoto to calculate NDVI
« Reply #2 on: March 18, 2018, 01:22:08 AM »
I've prepared a orthomosaic photo with 4 scales palette (black, red, yellow and green) and I would like to know how can I measure each color area.