[R-sig-Geo] Parse EWKT Polygon/MultiLineString/MultiPolygon Text

[Phillip Allen]

Hi all,

Years ago I wrote a short function (below) that parses a Extended Well Know
Text (EWKT) LineString field from PostGIS.  The code is below.  Unlike the
normal R sp functions this has XYZM values.

My problem is it was written for a simple linestring as seen below:
SRID=32611;LINESTRING(0 0 0 0,1 1 1 1,1 2 2 2 )

But now I need to parse multiLineString/multiPolygons, and Polygons all of
which have double & triple parentheses.
SRID=32611;POLYGON((0 0 0 0,4 0 0 1,4 4 2 3,0 4 2 4,0 0 3 5),(1 1 0 0, 2 1
2 2, 2 2 2 3, 1 2 3 4,1 1 0 5))
SRID=32611;MULTILINESTRING((0 0 0 0,1 1 0 1,1 2 2 2),(2 3 2 0,3 2 2 1,5 4 3
3))
SRID=32611;MULTIPOLYGON(((0 0 0 0,4 0 1 0,4 4 1 0,0 4 1 0,0 0 1 0),(1 1 1
0,2 1 1 0,2 2 1 0,1 2 1 0,1 1 0 0)), ((-1 -1 1 0,-1 -2 1 0,-2 -2 1 0,-2 -1
1 0,-1 -1 1 0)))

For the life of me I cannot think of an elegant way to parse it out without
a complicated for-each loop.  Does anyone have an idea of how to parse ewkt
(xyzm)?

I am using these to plot up vertical geological cross-sections in rgl's
plot3d/segments3d with bore-hole data such as this:
>segments3d(ewkt.xyzm2matrix(xsecD$gewkt) )

I hope one day soon sp can handle 2.5D data.

regards,
Phil

ewkt.xyzm2matrix <- function(t) {
# Converts Extented-Well-Know-Text Coordinates to XYZ Coordinate matrix
    t <- gsub("SRID=32611;LINESTRING", "", t)
    t <- unlist(substr(t, 2, nchar(t)-1 ))

    c <- 4
    r <-  length(unlist(strsplit(t,",")))

    t <- gsub(',', ' ', t)
    t <- as.double(unlist(strsplit(t," ")))

    tmat <- matrix(t, r, c, byrow=TRUE)
    tmat <- tmat[, 1:3]
return(tmat)
}

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