Feature Request: line_merge with direction

[latot]

Hi all, actually there is the line_merge which works great, now for some cases we need to preserve the direction of the vectors, at least in the actual version there is no docs about it, so from that is not guarantee to keep the direction of the vectors.

Would be great have a new param on the function which we can select, if the join must preserve the direction of the vectors.

IIRC, preserve has two aspects:

• End/Start points will be keep
• Only joins vectors that keep the right direction, the wrong direction can cause to a vector to not be join
• No idea what happens if there is 4 vectors, 2 in right direction, and other 2 in the right direction

Here some docs: https://postgis.net/docs/ST_LineMerge.html

IIRC geos has an option for that.

Thx!

[edzer]

library(sf)
# Linking to GEOS 3.11.1, GDAL 3.6.4, PROJ 9.1.1; sf_use_s2() is TRUE

(x = st_multilinestring(list(rbind(c(0,0), c(1,0)), rbind(c(2,0), c(1,0)))))
# MULTILINESTRING ((0 0, 1 0), (2 0, 1 0))
st_line_merge(x)
# LINESTRING (0 0, 1 0, 2 0)
st_line_merge(x, directed = FALSE)
# LINESTRING (0 0, 1 0, 2 0)
st_line_merge(x, directed = TRUE)
# MULTILINESTRING ((0 0, 1 0), (2 0, 1 0))