fix and export homedist

[mdsumner]

Updated in master, but add tests and more flexibility to specify what "home" is.

https://stat.ethz.ch/pipermail/r-help/2016-June/439453.html

[mdsumner]

This should be so much better:

#' Return all trip records where the maximum distance the start is reached. 
#' Use argument `home` to specify an arbitrary location, otherwise the individual
#' trip's first location is used. The maximum distance is returned in new column "max_home_dist_".
#' If trip is in longlat, result is in "km", otherwise in the units of `sp::proj4string(x)` (which is probably metres). 
homedist2 <- function (x, home = NULL)  {
        if (!is.null(home)) {
            if (is.numeric(home) & length(home) == 2) {
                home <- matrix(home, ncol = 2)
            }
            else {
                stop("stop, home must be a 2-element numeric")
            }
        }
        tor <- trip::getTORnames(x)
        ids <- unique(x[[tor[2L]]])
        
        
        longlat <- !is.projected(x)
        if (is.na(longlat)) {
            longlat <- TRUE
            warning("coordinate system is NA, assuming longlat . . .")
        }
        out <- vector("list", length(ids))
        for (i in seq_along(ids)) {
            x0 <- coordinates(x[x[[tor[2L]]] == ids[i], ])
            if (is.null(home)) 
                home <- x0[1, , drop = FALSE]
            dists <- spDistsN1(x0, home, longlat = longlat)
            idx <- which.max(dists)
            out[[i]] <- as.data.frame(x0)[idx, , drop = FALSE]
            out[[i]][["max_home_dist_"]] <- dists[idx]
        }
        do.call(rbind, out)
    }


## Example
library(trip)
data("walrus818")
maxdist_rows <- homedist2(walrus818)

plot(walrus818); lines(walrus818)
## this object has odd names for x, y
points(maxdist_rows[, c("X_AED170_70", "Y_AED170_70")], col = "firebrick", pch = 19, cex = 4)

[mdsumner]

See also #9

• some fixes already in post-1.5.0

[mdsumner]

implemented in traipse