vegIndex: Vegetation indices from surface reflectance

In adamlilith/fasterRaster: Faster Raster and Spatial Vector Processing Using 'GRASS GIS'

Vegetation indices from surface reflectance

Description

This function calculates one of many types of vegetation indices from a raster with four bands representing blue (B), green (G), red (R), and near infrared (NIR), plus possibly channels 5 and 7. The function requires rasters that represent surface reflectance, so should have values that fall in the range 0 to 1, unless they are digital number rasters (e.g., integers in the range 0 to 255). If digital number format is used, then the bits argument should be defined.

Usage

## S4 method for signature 'GRaster'
vegIndex(
  x,
  index = "NDVI",
  r = NULL,
  g = NULL,
  b = NULL,
  nir = NULL,
  b5 = NULL,
  b7 = NULL,
  soilSlope = NULL,
  soilIntercept = NULL,
  soilNR = 0.08,
  bits = NULL
)

Arguments

x	A GRaster with one layer per required band. Values should be between 0 and 1.
index	Character or character vector: The vegetation index or indices to calculate. You can find a list of available indices using fastData("vegIndices") (also see vegIndices). The first column, "index" provides the name of the index, and these are the values that this argument will accept (e.g., "NDVI", "EVI2"). Partial matching is used, and case is ignored. You can also use these shortcuts: "*": Calculate all indices "RNIR": Calculate all indices that use R and NIR channels (but not other channels). "NotSoil": Calculate all indices that use any channels but do not require soilSlope or soilIntercept. Note: A near-comprehensive table of indices can be found on the Index Database: A Database for Remote Sensing Indices.
r, g, b, nir	Numeric or character: Index or names() of the layers in x that represent the red, green, blue, and near infrared channels. Values must be in the range from 0 to 1 or integers.
b5, b7	Numeric or character: Index of names of the layers representing bands 5 and 7. These are used only for GVI and PVI. Values must be in the range from 0 to 1 or integers.
soilSlope, soilIntercept, soilNR	Numeric: Values of the soil slope, intercept, and soil noise reduction factor (0.08, by default). Used only for calculation of MSAVI.
bits	Either NULL (default) or numeric integer or integer with a value of 7, 8, 10, or 16: If the rasters are represented by integers (so do not fall in the range of 0 to 1), then the number of bits can be supplied using bits. If this is the case, then they will range from 0 to 2^n, where n is 7, 8, 10, or 16. If bit rasters are supplied, they must be of datatype() "integer". If raster values are in the range from 0 to 1, then bits should be NULL (default).

Value

A GRaster.

See Also

GRASS manual page for module i.vi (see grassHelp("i.vi"))

Examples

if (grassStarted()) {

# Setup
library(terra)

# Elevation raster, rivers vector
madLANDSAT <- fastData("madLANDSAT")

# Convert a SpatRaster to a GRaster:
landsat <- fast(madLANDSAT)

# See available vegetation indices:
vegIndices

# Normalized Difference Vegetation Index and Enhanced Vegetation Index:
indices <- c("ndvi", "evi")
vi <- vegIndex(landsat, index = indices, r = 1, b = 3, nir = 4, bits = 8)
plot(vi)

# All indices using R and NIR:
rnir <- vegIndex(landsat, index = "rnir", r = 1, nir = 4, bits = 8)

# Note: Some values are highly skewed, likely due to cloud cover and other
# anomalies that should be corrected.
plot(rnir)

}

adamlilith/fasterRaster documentation built on Oct. 26, 2024, 4:06 p.m.