rel.pi: Relative position index

In scapesClassification: User-Defined Classification of Raster Surfaces

Relative position index

Description

Compute the relative position index of raster objects.

Usage

rel.pi(attTbl, RO, el, type = "s", plot = FALSE, r = NULL)

Arguments

attTbl	data.frame, the attribute table returned by the function attTbl.
RO	column name, the name of the column with the raster object IDs.
el	column name, the name of column with the elevation values on which the relative position index is computed.
type	character, defines if position index values are standardized ("s") or normalized ("n").
plot	logic, plot the results.
r	single or multi-layer raster of the class SpatRaster (see help("rast", terra)) used to compute the attribute table. Required only if plot = TRUE.

Details

Position index values are computed only for cells that belong to a raster object.

• Standardized position index values (type="s") are computed with the formula ( x - mean(x) ) / sd(x);

• Normalized position index values (type="n") are computed with the formula ( x - min(x) ) / ( max(x) - min(x) );

• Variable x represents the elevation values of individual raster object.

Value

The function returns a vector with relative position index values. The vector has length equal to the number of rows of the attribute table. NA values are assigned to cells that do not belong to any raster object.

See Also

attTbl(), ngbList(), pi.add(), pi.sgm()

Examples

# DUMMY DATA
######################################################################################
# LOAD LIBRARIES
library(scapesClassification)
library(terra)

# LOAD THE DUMMY RASTER
r <- list.files(system.file("extdata", package = "scapesClassification"),
                pattern = "dummy_raster\\.tif", full.names = TRUE)
r <- terra::rast(r)

# COMPUTE THE ATTRIBUTE TABLE
at <- attTbl(r, "dummy_var")

# COMPUTE THE LIST OF NEIGBORHOODS
nbs <- ngbList(r, rNumb=TRUE, attTbl=at) # rnumb MUST be true to use obj.nbs

################################################################################
# COMPUTE RASTER OBJECTS
################################################################################
at$RO <- anchor.seed(at, nbs, silent=TRUE, class = NULL, rNumb=TRUE,
                     cond.filter = "dummy_var > 1",
                     cond.seed   = "dummy_var==max(dummy_var)",
                     cond.growth = "dummy_var<dummy_var[]",
                     lag.growth  = 0)

# Convert class vector at$RO to raster and plot
r_RO  <- cv.2.rast(r = r, classVector = at$RO)
terra::plot(r_RO, type="classes", main="Raster objects",
            plg=list(x=1, y=1, cex=0.9))

################################################################################
# STANDARDIZED RELATIVE POSITION INDEX
################################################################################
relPI <- rel.pi(attTbl = at, RO = "RO", el = "dummy_var",
                type = "s",
                plot = TRUE, r = r)

# Annotate relPI
points(terra::xFromCell(r, at$Cell[which(at$RO==1)]),
       terra::yFromCell(r, at$Cell[which(at$RO==1)]) - 0.04,
       pch=20, col="yellow")
points(terra::xFromCell(r, at$Cell[which(at$RO==2)]),
       terra::yFromCell(r, at$Cell[which(at$RO==2)]) - 0.04,
       pch=20, col="darkgreen")
text(xyFromCell(r,at$Cell), as.character(round(relPI,2)))
legend(1.02, 0.4, legend=c("1", "2"), bty = "n", title="RO:", xpd=TRUE,
col=c("#E6E600", "#00A600"), pch=20, cex=0.9, pt.cex = 1.5)

################################################################################
# NORMALIZED RELATIVE POSITION INDEX
################################################################################
# Compute normalized relative position index
relPI <- rel.pi(attTbl = at, RO = "RO", el = "dummy_var",
                type = "n",
                plot = TRUE, r = r)

# Annotate relPI
points(terra::xFromCell(r, at$Cell[which(at$RO==1)]),
       terra::yFromCell(r, at$Cell[which(at$RO==1)]) - 0.04,
       pch=20, col="yellow")
points(terra::xFromCell(r, at$Cell[which(at$RO==2)]),
       terra::yFromCell(r, at$Cell[which(at$RO==2)]) - 0.04,
       pch=20, col="darkgreen")
text(xyFromCell(r,at$Cell), as.character(round(relPI,2)))
legend(1.02, 0.4, legend=c("1", "2"), bty = "n", title="RO:", xpd=TRUE,
col=c("#E6E600", "#00A600"), pch=20, cex=0.9, pt.cex = 1.5)

scapesClassification documentation built on March 18, 2022, 6:32 p.m.