graph.statistics {GeNetIt}

Statistics for edges (lines)

Description

Extracts raster values for each edge and calculates specified statistics

Usage

graph.statistics(x, r, stats = c("min", "mean", "max"), buffer = NULL)

Arguments

x

sp SpatialLinesDataFrame or sf LINE object

r

A terra SpatRast or raster rasterLayer, rasterStack, rasterBrick object

stats

Statistics to calculate. If vectorized, can pass a custom statistic function.

buffer

Buffer distance, radius in projection units. For statistics based on edge buffer distance

Value

data.frame object of statistics

Note

If the buffer argument is specified that, raster values within the specified buffer radius are extracted and included in the derived statistic(s). Else-wise, the statistics are derived from raster values that directly intersect each edge.

Author(s)

Jeffrey S. Evans <[e-mail]> and Melanie A. Murphy <[e-mail]>

Examples

 library(sf)
 library(terra)  

 data(ralu.site)	
 xvars <- rast(system.file("extdata/covariates.tif", package="GeNetIt"))
 
  ( dist.graph <- knn.graph(ralu.site, row.names = ralu.site$SiteName, 
                            max.dist = 1500) )
 
 skew <- function(x, na.rm = TRUE) {  
           if (na.rm) x <- x[!is.na(x)]
           sum( (x - mean(x)) ^ 3) / ( length(x) * sd(x) ^ 3 )  
 		}

# Moments on continuous raster data
 system.time( {		
  stats <- graph.statistics(dist.graph, r = xvars[[-6]],  
              stats = c("min", "median", "max", "var", "skew")) 
 } ) 

# Proportional function on nominal raster data		
p <- function(x) { length(x[x < 52]) / length(x) }	
	
  system.time( {		
   nstats <- graph.statistics(dist.graph, r = xvars[[6]],
               stats = "p") 
  } ) 	

# Based on 500m buffer distance around line(s)
 system.time( {		
  stats <- graph.statistics(dist.graph, r = xvars[[-6]],  
              stats = c("min", "median", "max", "var", "skew"),
			      buffer = 500) 
 } )