I am trying to calculate index based built-up index (IBI) in ArcMap using raster calculator and getting strange values. I downloaded Landsat 8 data and using green, red, NIR and SWIR1 bands for the equation:
IBI = (NDBI - (SAVI + MNDWI) / 2) / (NDBI + (SAVI + MNDWI) / 2)
I followed the equations in this article to get all the indexes needed for IBI https://link.springer.com/article/10.1007%2Fs10708-020-10148-w
My result values for IBI range from -3.10538e+07 to 2.53846e+07, which is rather strange. My NDBI values range from -0.64 to 0.66, SAVI from -0.33 to 1.47, MNDWI from -0.98 to 0.47. All these 3 rasters seem to correct. I can't really get my head around where the mistake is.
Any suggestion? I would be really grateful for any help.
Well I tried setting your variables to their lowest values:
ndbi = -0.64
savi = -0.33
mndwi = -0.98
Then pumped them into your equation and it generate:
ibi = (ndbi - (savi + mndwi)/2)/(ndbi+(savi+mndwi)/2)
ibi = -0.011583011583011595
Which is nothing like your erroneous values, so unless you show us how you ran the tools no one is going to be able to help you.
You must add 1 to the NDBI, SAVI, and MNDWI to have the results of IBI.