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Find relationship between number of nodes and threshold area in an OCN

find_area_threshold_OCN.Rd

Function that calculates relationship between threshold area and number of nodes at RN and AG level for a given OCN. It can be used prior to application of aggregate_OCN in order to derive the drainage area threshold that corresponds to the desired number of nodes of the aggregated network. It is intended for use with single outlet OCNs, although its use with multiple outlet OCNs is allowed (provided that max(thrValues) <= min(OCN$CM$A)).

Usage

find_area_threshold_OCN(OCN, thrValues = seq(OCN$cellsize^2,
  min(OCN$CM$A), OCN$cellsize^2), maxReachLength = Inf,
  streamOrderType = "Strahler", displayUpdates = 0)

Arguments

OCN

A river object as produced by landscape_OCN

thrValues

Vector of values of threshold drainage area (in squared planar units) for which the respective number of nodes at the RN and AG levels are computed. Note that it must be max(thrValues) <= min(OCN$CM$A), otherwise the catchment(s) with area lower than max(thrValues) degenerate to a network with zero nodes at the RN/AG level.

maxReachLength

Maximum reach length allowed (in planar units). If the path length between a channel head and the downstream confluence is higher than maxReachLength, the reach starting from the channel head will have a length up to maxReachLength, while the next downstream pixel is considered as a new channel head, from which a new reach departs.

streamOrderType

If "Strahler", Strahler stream order is computed; if "Shreve", Shreve stream order is computed.

displayUpdates

If 1, progress updates are printed in the console while the function is running. If 0, no updates are printed.

Value

A list whose objects are listed below.

thrValues

Copy of the input vector with the same name.

nNodesRN

Vector (of the same length as thrValues) of number of nodes at the RN level resulting from the aggregation process with a threshold area values specified by thrValues.

nNodesAG

Vector (of the same length as thrValues) of number of nodes at the AG level resulting from the aggregation process with a threshold area values specified by thrValues.

drainageDensity

Vector (of the same length as thrValues) of values of drainage density of the river network resulting from the aggregation process with a threshold area values specified by thrValues. Drainage density is calculated as total length of the river network divided by area of the lattice. It is expressed in planar units^(-1).

streamOrder

Vector (of the same length as thrValues) of values of maximum stream order attained by the river network, resulting from the aggregation process with a threshold area values specified by thrValues.

Examples

# 1) derive relationship between threshold area and number of nodes
OCN <- landscape_OCN(OCN_20)
thr <- find_area_threshold_OCN(OCN)
# log-log plot of number of nodes at the AG level versus 
# relative threshold area (as fraction of total drainage area) 
old.par <- par(no.readonly = TRUE)
par(mai = c(1,1,1,1))  
plot(thr$thrValues[thr$nNodesAG > 0]/OCN$CM$A,
    thr$nNodesAG[thr$nNodesAG > 0], log = "xy",
    xlab = "Relative area threshold", ylab = "Number of AG nodes")

par(old.par)