ForestTools (version 0.2.5)

vwf: Variable Window Filter

Description

Implements the variable window filter algorithm (Popescu & Wynne, 2004) for detecting treetops from a canopy height model.

Usage

vwf(
  CHM,
  winFun,
  minHeight = NULL,
  maxWinDiameter = 99,
  minWinNeib = "queen",
  verbose = FALSE
)

Arguments

CHM

Canopy height model. Either in raster format, or a path directing to a raster file. A character vector of multiple paths directing to a tiled raster dataset can also be used.

winFun

function. The function that determines the size of the window at any given location on the canopy. It should take the value of a given CHM pixel as its only argument, and return the desired *radius* of the circular search window when centered on that pixel. Size of the window is in map units.

minHeight

numeric. The minimum height value for a CHM pixel to be considered as a potential treetop. All CHM pixels beneath this value will be masked out.

maxWinDiameter

numeric. Sets a cap on the maximum window diameter (in cells). If an improperly calibrated function is set for winFun, it may produce overly large windows that would perform poorly and significantly slow processing time. This setting can be disabled by setting to NULL.

minWinNeib

character. Define whether the smallest possible search window (3x3) should use a queen or a rook neighborhood.

verbose

logical. Print progress to console if set to TRUE.

Value

SpatialPointsDataFrame. The point locations of detected treetops. The object contains two fields in its data table: height is the height of the tree, as extracted from the CHM, and winRadius is the radius of the search window when the treetop was detected. Note that winRadius does not necessarily correspond to the radius of the tree's crown.

Details

This function uses the resolution of the raster to figure out how many cells the window needs to cover. This means that the raster value (representing height above ground) and the map unit (represented by the raster's resolution), need to be in the _same unit_. This can cause issues if the raster is in lat/long, whereby its resolution is in decimal degrees.

References

Popescu, S. C., & Wynne, R. H. (2004). Seeing the trees in the forest. Photogrammetric Engineering & Remote Sensing, 70(5), 589-604.

See Also

mcws sp_summarise

Examples

# NOT RUN {
# Set function for determining variable window radius
winFunction <- function(x){x * 0.06 + 0.5}

# Set minimum tree height (treetops below this height will not be detected)
minHgt <- 2

# Detect treetops in demo canopy height model
ttops <- vwf(CHMdemo, winFunction, minHgt)

# }