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Split NODATA values or create matrix for reclassification

Source: R/split_nodata_values.R
split_nodata_values.Rd

Internal functions: split_nodata_values splits the ranges of NODATA saved in the xml product file to a readable vector of NoData values; create_nodata_rcl creates the matrix for the reclassification of NODATA values to be used with raster::reclassify function.

Usage

split_nodata_values(nodata_in, take_all = TRUE)

create_nodata_rcl(nodata_in, nodata_out)

Arguments

nodata_in

Character vector corresponding to input NoData values as saved in the xml product file (one or more values per band).

take_all

Logical: if TRUE (default), all the NoData values are considered; if FALSE, only the last one is taken. See "details" for the meaning of this parameter.

nodata_out

Character vector corresponding to output NoData values as saved in the xml product file (one single value per band).

Value

split_nodata_values returns a list with the same length of nodata_in vector, in which each element is a vector with all the NoData values.

create_nodata_rcl returns a list of matrices in the format specified for parameter rcl in raster::reclassify. The parameter right is intended to be used as right = NA.

Details

MODIS products can have more than one NoData values (sometimes with different meanings, e.g. 255 = "fill" and 254 = "detector saturated" in MOD09A1 product). By setting "Change NoData values" to "Yes" in the GUI, all the NoData values are coerced to one single new NoData value; conversely, setting it to "No" only one value is assumed to be NoData. The parameter take_all is assumed to be used in this way, by using this function with take_all = TRUE with "Change NoData values" = "Yes" and take_all = FALSE with "Change NoData values" = "No".

In the xml product file, NoData ranges are set as:

  • x for products with single NoData values;

  • x,y,z for products with a vector of NoData values;

  • x:y for products with a range of NoData values;

  • x:y,z for a combination of NoData ranges and/or values.

In split_nodata_values NoData values are assumed to be integer: this means that intervals are splitted in integer values (e.g. "250:255" becomes "250 251 252 253 254 255"). Conversely, function create_nodata_rcl creates intervals, so it can also manage float values (in practice, this should not make difference within MODIS products, since NoData values are always integer values).

This function interprets these strings and convert them in vectors with single values. Notice that the first NoData value is the only one which is considered if 'Change NoData values' was set to 'No'.

Author

Luigi Ranghetti, phD (2018)

Examples

MODIStsp:::create_nodata_rcl(c("255","250,254:255"), c("255","255"))
#> [[1]]
#>      from  to becomes
#> [1,]  255 255     255
#> 
#> [[2]]
#>      from  to becomes
#> [1,]  250 250     255
#> [2,]  254 255     255
#>