Removed TGI plant health equation

[rion-saeon]

I realised the TGI equation may be erroneous thus I removed it. I am surprised that no one questioned it before so hopefully it was not used much.

[Saijin-Naib]

Oooh, interesting. Do you have any literature or examples?

Is our implementation flawed, or is the index itself flawed?

[rion-saeon]

@Saijin-Naib the index I added are presumably flawed (from a source I cannot recall). Here is a correct version when camera wavelengths are unknown (a typical scenario for drone, kite etc. pilots). If someone could implement these equations (2-4 from this paper), it would be great because TGI seems to be a gold standard these days when it comes to veg' health indices produced from RGB sensors.

[rion-saeon]

I could not replicate the n-TGI equation with results. It may be safer to use this (which performs as expected): A visible band index for remote sensing leaf chlorophyll content at the canopy scale