PVI Algorithm Specification |

### PVI

The Perpendicular Vegetation Index algorithm was first described by Richardson and Wiegand (1977).
This could be considered a generalization of the DVI which allows for soil lines of different slopes.
PVI is quite sensitive to atmospheric variations, (Qi et al., 1994).
Consequently, comparing PVI values for data taken at different dates is hazardous unless an atmospheric correction is performed on the data.

The PVI results from the following equation:

PVI = sin(a) * IR_factor * near_IR - cos(a) * red_factor * red

where: a is the angle between the soil line and the NIR axis, in degrees.

### PVI-Flags

Also the processor computes an additional flags band called 'pvi_flags' with the following bit coding:

Bit Position | Description
--- | ---
Bit 0 | The computed value for PVI is NAN or is Infinite
Bit 1 | The computed value for PVI is less than -1 (minus one)
Bit 2 | The computed value for PVI is greater than 1 (one)