Calculates distances between locations and sampling sites based on detection range.

Determine de euclidean distance from each occurrence to each survey (point), and mantain only the distances to each survey unit for occurrences inside a limiting distance of detection

pointSample(sites, occ, radius)

Arguments

sites

Data.frame with position (x, y) for each point survey (in rows).

occ

Data.frame with position (x, y) for each occurrence (in rows).

radius

A numeric value indicating the maximum distance of detection of the occurrence point in the survey.

Details

Value

Returns a list with a matrix with occ (rows) x sites (cols) with values of distance if less than radius, otherwise NA.

References

Author

Note

See also

Examples

set.seed(1234)

# Generate random occurrences and sampling sites
obs <- data.frame(x=runif(1000, 0, 100), y=runif(1000, 0, 100))
sites <- randomSamp(25, c(0, 100), c(0, 100), 20)

#Get the distance matrix from a point sampling procedure with detection radius of 5 units
detrange <- 5
psamp <- pointSample(sites, obs, radius = detrange)

plot(obs, cex=0.3, asp=1)
points(sites, cex=0.6, pch=3, col='red')
points(sites, cex=detrange, pch=21, col='red', bg = NULL)

for (i in 1:nrow(sites)) {
  d <- psamp$distance[,i]
  msk <- !is.na(d)
  col <- as.integer(cut(d[msk], seq(0, detrange, length.out=5)))
  points(obs[msk,], pch=16, cex=1, col=rainbow(10)[col]) 
}