Add function to split a line into n segments or segments of a given length about stplanr HOT 6 CLOSED

#' Find the mid-point of lines
#'
#' This is a wrapper around \code{\link{SpatialLinesMidPoints}} that allows it to find the midpoint
#' of lines that are not projected, which have a lat/long CRS.
#' @inheritParams line2df
#' @export
#' @examples
#' l = routes_fast
line_midpoint = function(l){
  gprojected(l, maptools::SpatialLinesMidPoints)
}

#' Calculate length of lines in geographic CRS
#' @inheritParams line2df
#' @param byid Logical determining whether the length is returned per object (default is true)
#' @export
line_length = function(l, byid = TRUE){
  gprojected(l, rgeos::gLength, byid = byid)
}

#' Divide SpatialLines dataset into regular segments
#' @inheritParams line2df
#' @param n_segments The number of segments to divide the line into
#' @param segment_length The approximate length of segments in the output (overides n_segments if set)
#' @export
#' @examples
#' l = routes_fast[1,]
#' l_seg2 = line_segment(l = l, n_segments = 2)
#' plot(l_seg2, col = l_seg2$group, lwd = 50)
#' l_seg5 = line_segment(l = l, n_segments = 5)
#' plot(l_seg5, col = l_seg5$group, lwd = 30, add = TRUE)
#' l_seg100m = line_segment(l = l, segment_length = 100)
#' plot(l_seg100m, col = l_seg100m$group, lwd = 10, add = TRUE)
#' plot(l, col = "white", add = TRUE)
#' line_segment(l = l, segment_length = 100)
line_segment = function(l, n_segments, segment_length = NA){
  if(!is.na(segment_length)){
    l_length = line_length(l)
    n_segments = round(l_length / segment_length)
  }
  if(n_segments == 2){
    pseg = line_midpoint(l)
  } else {
    pseg = spsample(x = l, n = n_segments - 1, type = "regular")
  }
  l_geom = raster::geom(l)
  l_coords = l_geom[, c("x", "y")]
  knn_res = nabor::knn(data = l_coords, query = coordinates(pseg), k = 1)
  sel_nearest = c(knn_res$nn.idx)
  for(i in 1:(length(sel_nearest) + 1)){
    ids = c(1, sel_nearest, nrow(l))
    if(i == 1){
      l_seg = points2line(l_coords[ids[i]:ids[(i + 1)],])
      spChFIDs(l) = i
    } else if(i == length(sel_nearest) + 1){
      l_temp = points2line(l_coords[ids[i]:nrow(l_coords),])
      spChFIDs(l_temp) = i
      l_seg = maptools::spRbind(l_seg, l_temp)
    } else {
      l_temp = points2line(l_coords[ids[i]:ids[(i + 1)],])
      spChFIDs(l_temp) = i
      l_seg = maptools::spRbind(l_seg, l_temp)
    }
  }
  SpatialLinesDataFrame(l_seg, data.frame(group = 1:i))
}