Create a Sentinel Hub API Evalscript

Generates a JavaScript evaluation script for calculating a spectral index for Sentinel-1, Sentinel-2 or Landsat-8/9 imagery.

Usage

MakeEvalScript(
  x,
  ...,
  constellation = c("sentinel-1", "sentinel-2", "landsat")
)

Arguments

x

A character string with the short_name of a spectral index from rsi::spectral_indices() or a single-row data.frame (or list) with the elements bands, formula, platforms, and optionally long_name.

...

Named arguments providing values for any constants required by the index's formula. The function will stop if a required constant is missing and warn if unused arguments are provided.

constellation

character indicating the constellation for which the script should be generated. Must be one of "sentinel-1", "sentinel-2", or "landsat".

Value

A `character` vector containing the JavaScript evalscript. It can be used as `script` argument in functions that require one as shown here:

..., script = paste(MakeEvalScript("NDVI"), collapse = "\n"), ....

It can also be saved to a file for later use or further modifications.

Details

This function takes a spectral index definition and creates a JavaScript evaluation script compatible with the Sentinel Hub API. The index can be specified by its short name from the rsi package's spectral index database (see rsi::spectral_indices()) or as a custom list or data.frame.

The function automatically maps common band names (e.g., `N`, `R`, `G`, `B`) to the corresponding Sentinel-1, Sentinel-2 or Landsat-8/9 band names required by the API, based on the value of the constellation argument. Any constants in the index formula (e.g., the soil adjustment factor `L` in SAVI) must be provided as named arguments.

Examples

if (FALSE) { # \dontrun{

# NDVI
si <- rsi::spectral_indices() # retrieves spectral indices
ndvi <- subset(si, short_name == "NDVI") # creates one-row data.frame
ndvi_script <- MakeEvalScript(ndvi, constellation = "sentinel-2") # generates the script
cat(ndvi_script, sep = "\n")

# SAVI, which requires the constant L
cat(MakeEvalScript("SAVI", L = 0.5), sep = "\n", file = "SAVI.js")

# Using a custom index definition as a data.frame
custom_index <- data.frame(
  short_name = "GNDVI",
  long_name = "Green Normalized Difference Vegetation Index",
  platforms = I(list("Sentinel-2")),
  bands = I(list(c("N", "G"))),
  formula = "(N - G) / (N + G)"
)
cat(MakeEvalScript(custom_index, constellation = "landsat"))
} # }