distfilter {SDLfilter} | R Documentation |
Filter locations by distance
Description
This function removes locations that are located beyond a specified distance.
Usage
distfilter(sdata, max.dist = 100, method = 1, ia = NA)
Arguments
sdata |
A data frame containing columns with the following headers: "id", "DateTime", "lat", "lon".
See the data |
max.dist |
A numeric value specifying a threshold of distance between successive locations. Default is 100 km. |
method |
An integer specifying how locations should be filtered with max.dist. A location is removed if the distance from a previous and(1)/or(2) to a subsequent location exceeds max.dist. Default is 1 (both way). |
ia |
An integer (0 to 180) specifying an inner angle (in degrees) between consecutive locations, beyond which the locations are considered potential outliers. Default (NA) ignores this option. See details. |
Details
This function removes locations if the distance from a previous and/or to a subsequent location exceeds max.dist and the inner angle is less than ia. If ia is NA (default), inner angles are not considered in the filtering.
Value
The input data is returned without locations identified by this filter. The following columns are added: "pDist", "sDist", 'inAng'. "pDist" and "sDist" are straight distances in kilometres from a previous and to a subsequent fix respectively. "inAng" is the degree between the bearings of lines joining successive location points.
Author(s)
Takahiro Shimada
Examples
#### Load data sets
## Fastloc GPS data obtained from a green turtle
data(turtle)
## A Map for the example site
data(Australia)
data(SandyStrait)
#### Filter temporal and/or spatial duplicates
turtle.dup <- dupfilter(turtle, step.time=1/60, step.dist=0.001)
#### distfilter
turtle.dist <- distfilter(turtle.dup, max.dist = 50, ia = 20)
#### Plot data removed or retained by ddfilter
## Entire area
p1 <- to_map(turtle.dup, bgmap=Australia, point.size = 2, line.size = 0.5, axes.lab.size = 0,
multiplot = FALSE, point.bg = "red",
title.size=15, title="Entire area")[[1]] +
geom_point(aes(x=lon, y=lat), data=turtle.dist, size=2, fill="yellow", shape=21)+
geom_point(aes(x=x, y=y), data=data.frame(x=c(154, 154), y=c(-22, -22.5)),
size=3, fill=c("yellow", "red"), shape=21) +
annotate("text", x=c(154.3, 154.3), y=c(-22, -22.5), label=c("Retained", "Removed"),
colour="black", size=4, hjust = 0)
## Zoomed in
p2 <- to_map(turtle.dup, bgmap=SandyStrait, xlim=c(152.7, 153.2), ylim=(c(-25.75, -25.24)),
axes.lab.size = 0, point.size = 2, point.bg = "red", line.size = 0.5,
multiplot = FALSE, title.size=15, title="Zoomed in")[[1]] +
geom_path(aes(x=lon, y=lat), data=turtle.dist, linewidth=0.5, colour="black", linetype=1) +
geom_point(aes(x=lon, y=lat), data=turtle.dist, size=2, colour="black", shape=21, fill="yellow")
gridExtra::marrangeGrob(list(p1, p2), nrow=1, ncol=2)