Identify local maxima or minima

Identify local maxima or minima on a raster surface.

peak.cell(attTbl, ngbList, rNumb = FALSE, p_col, p_fun = "max", p_edge = FALSE)

Arguments

attTbl

data.frame, the attribute table returned by the function attTbl.

ngbList

list, the list of neighborhoods returned by the function ngbList.

rNumb

logic, the neighborhoods of the argument ngbList are identified by cell numbers (rNumb=FALSE) or by row numbers (rNumb=TRUE) (see ngbList). It is advised to use row numbers for large rasters.

p_col

character, the column of the attribute table over which maxima or minima are searched.

p_fun

character, if 'max' the function searches for local maxima; if 'min' the function searches for local minima.

p_edge

logic, if false local maxima or minima are not searched on edge cells. Edge cells are considered cells on the edge of the raster and cell neighboring NA-cells.

Value

A classVector with peak cells identified by the numeric class 1. See conditions for more details about class vectors.

Details

• A cell constitutes a local maximum if its elevation value is larger than the values of all the cells in its neighborhood (see ngbList).

• A cell constitutes a local minimum if its elevation value is smaller than the values of all the cells in its neighborhood (see ngbList).

See also

conditions(), attTbl(), ngbList()

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)
################################################################################

# PEAK.CELL
################################################################################
# p_edge = FALSE
pc_a <- peak.cell(attTbl = at, ngbList = nbs, rNumb = FALSE,
                  p_col = "dummy_var", p_fun = "max", p_edge = FALSE)

# p_edge = TRUE
pc_b <- peak.cell(attTbl = at, ngbList = nbs, rNumb = FALSE,
                  p_col = "dummy_var", p_fun = "max", p_edge = TRUE)

# CONVERT THE CLASS VECTORS INTO RASTERS
r_pca <- cv.2.rast(r, at$Cell, classVector = pc_a, plot = FALSE)
r_pcb <- cv.2.rast(r, at$Cell, classVector = pc_b, plot = FALSE)
################################################################################

#PLOTS
###############################################################################
oldpar <- par(mfrow = c(1,2))
m <- c(4, 1, 4, 1)

# PLOT 1 - p_edge = FALSE
plot(r_pca, axes=FALSE, legend=FALSE, asp=NA, mar=m,
     colNA="#818792", col=c("#78b2c4", "#cfad89"))
text(r)
mtext(side=3, line=1, adj=0, cex=1, font=2, "PEAK.CELL")
mtext(side=3, line=0, adj=0, cex=0.9, "p_edge = FALSE")
legend("bottomright", bg = "white",
       legend = c("Peak cell", "Unclassified cells"),
       fill = c("#cfad89", "#818792"))

# PLOT 2 - p_edge = TRUE
plot(r_pcb, axes=FALSE, legend=FALSE, asp=NA, mar=m,
    colNA="#818792", col=c("#78b2c4", "#cfad89"))
text(r)
mtext(side=3, line=1, adj=0, cex=1, font=2, "PEAK.CELL")
mtext(side=3, line=0, adj=0, cex=0.9, "p_edge = TRUE")
legend("bottomright", bg = "white",
       legend = c("Peak cell", "Unclassified cells"),
       fill = c("#cfad89", "#818792"))

par(oldpar)