alibi_query: alibi_query

In markvregel/STPtrajectories: Space-time prism trajectories

Description

This function tests wether there was a possible meeting between two individuals or other moving objects. If the individuals of two trajecories could have met, is tested by applying the alibi query to segments that overlap in time. The alibi query is a Boolean query that checks whether two moving individuals, that are given by two samples of space-time points and speed limitations, could have met each other. The query tests if two space-time prisms intersect. Kuijpers et al. (2011) provide the analytical solution for the alibi query that is used by this function.

Usage

alibi_query(STP_track1, STP_track2, stop_if_true = TRUE, return_PIA = FALSE,
  time_interval = 5)

Arguments

STP_track1	STP_track1
STP_track2	STP_track2
stop_if_true	logigal:Stop if intersection is found. Default=TRUE
return_PIA	logigal:Return potential meeting time and Potential Intersection Area(PIA). Default=FALSE
time_interval	Accuracy in seconds of Potential Intersection Area(PIA) and time period that individuals could have been at the same location. Default is 5 seconds, meaning that time period and PIA are based on PPAs calculated for every 5 seconds.

Value

If an intersection is found, the method returns a vector with space-time point of intersecting STPs. If return_PIA is True, the method returns the Potential Intersection Area(PIA) and the time period that the individuals could have been at the same location. If no intersection is found, the methods returns FALSE.

Author(s)

Mark ten Vregelaar

References

- Kuijpers, B., Grimson, R., & Othman, W. (2011). An analytic solution to the alibi query in the space-time prisms model for moving object data. International Journal of Geographical Information Science, 25(2), 293-322.

Examples

library(spacetime)
library(sp)

## create 2 STP_tracks
# time
t1 <- strptime("01/01/2017 00:00:00", "%m/%d/%Y %H:%M:%S")
t2 <- t1+5*60*60 # 5 hours after t1
time1<-seq(t1,t2,30*60)
time2<-time1+0.25*60*60
# spatial coordinates
x1=c(seq(0,25,5),seq(27.5,37.5,2.5))
y1=sample(-2:2, 11,replace = TRUE)
x2=c(seq(0,25,5),seq(27.5,37.5,2.5))
y2=sample(-2:2, 11,replace = TRUE)

n = length(x1)
crs_NL = CRS("+init=epsg:28992")

# create class STIDF
stidf1 = STIDF(SpatialPoints(cbind(x1,y1),crs_NL), time1, data.frame(co2 = rnorm(n),O2=rnorm(n)))
stidf2 = STIDF(SpatialPoints(cbind(x2,y2),crs_NL), time2, data.frame(co2 = rnorm(n),O2=rnorm(n)))

# Track-class {trajectories}
my_track1<-Track(stidf1)
my_track2<-Track(stidf2)
# set maximum speed
v1<-getVmaxtrack(my_track1)+0.00015
v2<-getVmaxtrack(my_track2)+0.00030
# STP_track class
STP_track1<-STP_Track(my_track1,v1)
STP_track2<-STP_Track(my_track2,v2)

## the alibi query
alibi_query(STP_track1,STP_track2) # now only finds first intersection

markvregel/STPtrajectories documentation built on May 21, 2019, 12:25 p.m.