ForestGapR (version 0.1.7)

getForestGaps: Forest Canopy Gap Detection

Description

This function detects forest canopy gaps on Airborne Laser Scanning(ALS)-derived Canopy Height Model (CHM).

Usage

getForestGaps(chm_layer, threshold=10, size=c(1,10^4))

Value

Forest Gaps. An object of the class RasterLayer.

Arguments

chm_layer

ALS-derived Canopy Height Model (CHM) (raster::RasterLayer) object. An object of the class raster::RasterLayer.

threshold

Height threshold for gap detection. Default is 10 m.

size

A vector containing the minimum and maximum gap size - area (m2). Gaps with area < size[1] or area > size[2] are not considered. Default is 1 m2 and 1ha.

Author

Carlos Alberto Silva.

Examples

# =======================================================================#
# Importing ALS-derived Canopy Height Model (CHM)
# =======================================================================#
# Loading raster and viridis libraries
library(raster)
library(viridis)


# ALS-derived CHM over Adolpho Ducke Forest Reserve - Brazilian tropical forest
data(ALS_CHM_DUC)

# Plotting chm
plot(ALS_CHM_DUC, col = viridis(10), main = "ALS CHM")
grid()
# =======================================================================#
# Example 1: Forest Gap detection using a fixed canopy height thresholds
# =======================================================================#

# set height thresholds (e.g. 10 meters)
threshold <- 10
size <- c(1, 10^4) # m2

# Detecting forest gaps
gaps_duc <- getForestGaps(chm_layer = ALS_CHM_DUC, threshold = threshold, size = size)

# Ploting gaps
plot(gaps_duc, col = "red", add = TRUE, main = "Forest Canopy Gap", legend = FALSE)

# =======================================================================#
# Example 2: Gap detection using multiple canopy height thresholds
# =======================================================================#

# set the height thresholds
nthresholds <- c(10, 15, 20, 25)
size <- c(1, 10^4) # m2

# creating an empy raster stack to store multiple gaps as RasterLayers
gaps_stack <- stack()

# Gap detection
for (i in nthresholds) {
  gaps_i <- getForestGaps(chm_layer = ALS_CHM_DUC, threshold = i, size = size)
  names(gaps_i) <- paste0("gaps_", i, "m")
  gaps_stack <- stack(gaps_stack, gaps_i)
}

# plot gaps
oldpar <- par(no.readonly = TRUE)
par(mfrow = c(2, 2))
plot(ALS_CHM_DUC, col = viridis(10), main = "Height threshold 10m")
plot(gaps_stack$gaps_10m, col = "red", add = TRUE, legend = FALSE)

plot(ALS_CHM_DUC, col = viridis(10), main = "Height threshold 15m")
plot(gaps_stack$gaps_15m, col = "red", add = TRUE, legend = FALSE)

plot(ALS_CHM_DUC, col = viridis(10), main = "Height threshold 20m")
plot(gaps_stack$gaps_20m, col = "red", add = TRUE, legend = FALSE)

plot(ALS_CHM_DUC, col = viridis(10), main = "Height threshold 25m")
plot(gaps_stack$gaps_25m, col = "red", add = TRUE, legend = FALSE)
par(oldpar)