Spatial-temporal moving average

For each event, the mean centre of the span events centred on it in time order (ties in input order), the window shortened at the ends of the series. It traces how the centre of a series of incidents moves over time. It is a descriptive device of the crime-mapping literature with no original paper to cite; the mean centre is that of cgstat().

Usage

stmavg(x, y = NULL, t, span = 5, lonlat = FALSE)

Arguments

x, y

The points: x and y numeric vectors of equal length; or x a matrix or data frame with columns named x and y (or X and Y, as sf::st_coordinates() names them, or lon and lat with lonlat = TRUE) and y NULL; or x an sf or sfc object of POINT geometries, whose coordinate reference system must agree with lonlat. An unnamed two-column matrix is read as x then y; other columns are never taken by position. Vectors given separately (x, y, and w or t where a function takes them) are matched by name when every one is named and no name repeats, as elsewhere in the package; otherwise by position. No missing or infinite values.

t

The time of each event: finite numbers (for dates, as.numeric() of them, in days or seconds).

span

The window: one odd whole number from 1.

lonlat

FALSE (the default) when x and y are planar coordinates in one length unit; TRUE when they are longitude and latitude in degrees, which are then projected to metres by eqproj() about their own centre, and centres are returned in degrees. It is never guessed.

Value

A data frame with one row per event, in input order: mx, my (the window's mean centre, in degrees when lonlat = TRUE) and n (events in the window).

Examples

stmavg(x = 1:7, y = c(1, 1, 2, 3, 5, 8, 13), t = 7:1, span = 3)
#>    mx        my n
#> 1 1.5  1.000000 2
#> 2 2.0  1.333333 3
#> 3 3.0  2.000000 3
#> 4 4.0  3.333333 3
#> 5 5.0  5.333333 3
#> 6 6.0  8.666667 3
#> 7 6.5 10.500000 2