Skip to contents

Extract Main Ridge Lines from dtm

extract_main_ridges.Rd

This function identifies and extracts the main ridge lines based on flow accumulation values from inverted dtm. It selects the top N ridge tributaries by maximum flow accumulation, merges segments within each tributary, and returns the result with ranking information.

Usage

extract_main_ridges(ridges, dtm, nr_main = 2, metrics, plot_result = FALSE)

Arguments

ridges

An sf object containing ridge line network with TRIB_ID attribute. This must be pre-extracted using extract_networks(dtm, type = "ridge", metrics = metrics). This parameter is REQUIRED.

dtm

A SpatRaster object (from terra package) representing the digital elevation model. Used for plotting only.

nr_main

Integer specifying the number of main ridges to extract. Default is 2.

metrics

A list containing pre-calculated geomorphometric metrics from calc_geomorph_metrics(). This parameter is REQUIRED. Must contain flow_acc_inverted for ridge analysis.

plot_result

Logical. Should the result be plotted? Default is FALSE.

Value

An sf object containing main ridge lines with attributes:

  • TRIB_ID: Tributary identifier

  • RANK: Ranking (1 = highest flow accumulation)

  • flow_acc_inverted_max: Maximum flow accumulation value for the tributary

  • geometry: LINESTRING geometry

Details

The function follows this workflow:

  1. Extract flow accumulation values at each ridge segment

  2. Aggregate by TRIB_ID to find maximum flow per tributary

  3. Select top N tributaries by flow accumulation

  4. Merge segments within each selected tributary

  5. Add RANK attribute (1 = highest flow)

Note: Flow accumulation is extracted from individual segments BEFORE merging to ensure accurate values. Some tools may merge first, leading to incorrect results.

Examples

if (FALSE) { # \dontrun{
dtm <- rast("path/to/dtm.tif")

# Calculate metrics (REQUIRED)
metrics <- calc_geomorph_metrics(dtm)

# Extract ridge network (REQUIRED)
ridges <- extract_networks(dtm, type = "ridge", metrics = metrics)

# Extract main ridges
main_ridges <- extract_main_ridges(
  ridges = ridges,
  dtm = dtm,
  nr_main = 2,
  metrics = metrics
)

} # }