Forum

Author Topic: importing a reflectance calibrated ortomosaic into Matlab  (Read 1525 times)

negreiro

  • Newbie
  • *
  • Posts: 3
    • View Profile
importing a reflectance calibrated ortomosaic into Matlab
« on: December 03, 2018, 06:45:13 AM »
Hello,

We are mapping a winter wheat experiment in an attempt to evaluate several vegetation indexes. We have used a Sequoia camera and followed the documented procedure to generate a reflectance calibrated orthomosaic (www.agisoft.com/pdf/PS_1.4_(IL)_Refelctance_Calibration.pdf). The orthomosaic was saved as a geotiff image without compression.

A similar procedure using the same photos and region of interest was done in pix4dmapper. The pixel values of the  reflectance calibrated map generated by pix4dmapper are recognized as a floating point number (single) between 0 and 1 by geotiffread() when importing data to Matlab. 

The issue we are facing is that the orthomosaic generated by Photoscan must be normalized after importing to Matlab using geotiffread(). However the normalization value is not documented. After importing to Matlab with geotiffread we are getting pixel values in 16 bits unsigned format.

If we divide each 16-bit pixel value by 65536 in order to obtain a reflectance value between 0 and 1, the resulting orthomosaic histogram is quite different (half value) from the one obtained from pix4dmapper.

What is the correct normalization factor in order to convert the 16-bit number associated with a pixel in the calibrated orthomosaic  to a reflectance value between 0 and 1? Thanks.


Alexey Pasumansky

  • Agisoft Technical Support
  • Hero Member
  • *****
  • Posts: 14813
    • View Profile
Re: importing a reflectance calibrated ortomosaic into Matlab
« Reply #1 on: December 03, 2018, 08:13:59 PM »
Hello negreiro,

In PhotoScan we are following MicaSense guidelines for the reflectance calibration of RedEdge / Sequoia cameras imagery:
https://support.micasense.com/hc/en-us/articles/215460518-What-are-the-units-of-the-Atlas-GeoTIFF-output-

You should use 32768 value to normalize the reflectance output from PhotoScan to 0 - 1 range.
Best regards,
Alexey Pasumansky,
Agisoft LLC