我认为问题可能是由函数本身引起的。当你查看这个函数的代码时,我们可以看到下面的开头部分。
if (class(points) == "SpatialPoints" && missing(withAttrs))
withAttrs = FALSE
if (class(points) == "SpatialPoints" && withAttrs == TRUE)
stop("A SpatialPoints object has no attributes! Please set withAttrs as FALSE.")
有时候,SpatialPointsDataFrame可能被识别为SpatialPoints。因此,该函数将把您的SpatialPointsDataFrame视为SpatialPoints,并不会在函数中保留属性。 您可以按照下面的代码对函数进行一些修改。
snapPointsToLines1 <- function (points, lines, maxDist = NA, withAttrs = TRUE, idField = NA)
{
if (rgeosStatus()) {
if (!requireNamespace("rgeos", quietly = TRUE))
stop("package rgeos required for snapPointsToLines")
}
else stop("rgeos not installed")
if (is(points, "SpatialPointsDataFrame")==FALSE && missing(withAttrs))
withAttrs = FALSE
if (is(points, "SpatialPointsDataFrame")==FALSE && withAttrs == TRUE)
stop("A SpatialPointsDataFrame object is needed! Please set withAttrs as FALSE.")
d = rgeos::gDistance(points, lines, byid = TRUE)
if (!is.na(maxDist)) {
distToLine <- apply(d, 2, min, na.rm = TRUE)
validPoints <- distToLine <= maxDist
distToPoint <- apply(d, 1, min, na.rm = TRUE)
validLines <- distToPoint <= maxDist
points <- points[validPoints, ]
lines = lines[validLines, ]
d = d[validLines, validPoints, drop = FALSE]
distToLine <- distToLine[validPoints]
if (!any(validPoints)) {
if (is.na(idField)) {
idCol = character(0)
}
else {
idCol = lines@data[, idField][0]
}
newCols = data.frame(nearest_line_id = idCol, snap_dist = numeric(0))
if (withAttrs)
df <- cbind(points@data, newCols)
else df <- newCols
res <- SpatialPointsDataFrame(points, data = df,
proj4string = CRS(proj4string(points)), match.ID = FALSE)
return(res)
}
}
else {
distToLine = apply(d, 2, min, na.rm = TRUE)
}
nearest_line_index = apply(d, 2, which.min)
coordsLines = coordinates(lines)
coordsPoints = coordinates(points)
mNewCoords = vapply(1:length(points), function(x) nearestPointOnLine(coordsLines[[nearest_line_index[x]]][[1]],
coordsPoints[x, ]), FUN.VALUE = c(0, 0))
if (!is.na(idField)) {
nearest_line_id = lines@data[, idField][nearest_line_index]
}
else {
nearest_line_id = sapply(slot(lines, "lines"),
function(i) slot(i, "ID"))[nearest_line_index]
}
if (withAttrs)
df = cbind(points@data, data.frame(nearest_line_id, snap_dist = distToLine))
else df = data.frame(nearest_line_id, snap_dist = distToLine,
row.names = names(nearest_line_index))
SpatialPointsDataFrame(coords = t(mNewCoords), data = df,
proj4string = CRS(proj4string(points)))
}
然后,使用这个新函数snapPointsToLines1,你可以获得你想要的属性。