On Wed, 6 Aug 2014, Daniel Rodolphe Schlaepfer wrote:
Thank you for the suggestion. Unfortunately, this does not work for my
application: I plot the polygon on top of other another plot where I
need the holes of the polygon to be transparent. For instance, I don’t
want the African countries in the following examples to be covered by
white:
library(maps)
map()
plot(polySP, density=10, angle=45, pbg=“white")
Obviously not, these are base graphics, and you have to consider the
plotting order:
plot(polySP, density=10, angle=45, pbg="white", axes=TRUE)
map(add=TRUE)
However, this was not the point that I try to ask about. My point is
that maptools/SpatialPolygons2PolySet does not translate into correct
PolySet objects as illustrated in my previous example.
Since you no longer need PolySet objects, why? Maybe the coercion method
can be fixed, but it is not a priority - patch welcomed.
Roger
Thanks,
Daniel
On Aug 6, 2014, at 12:52 PM, Roger Bivand <roger.biv...@nhh.no> wrote:
On Wed, 6 Aug 2014, Daniel Rodolphe Schlaepfer wrote:
Hello all,
I try to convert a sp SpatialPolygons object with a hole to a PBS PolySet
object - my ultimate goal is to plot the polygon with hatching considering the
hole.
The problem is not that you need a PolySet representation, but that you need to set the
polygon background explicitly to a value other than "transparent" using the
pbg= argument:
plot(polySP, density=10, angle=45, pbg="white")
or adjust par("bg") to suit. When hatching is used, polypath is not used, so
automatic handling of holes in the plot method is not available.
Roger
My problem is that maptools/SpatialPolygons2PolySet only produces PolySet
objects with increasing POS even for polygons with holes; however, the
documentation of PolySet indicates that “We adopt the convention that POS goes
from 1 to n along an outer boundary, but from n to 1 along an inner boundary,
regardless of rotational direction.”
#Create simple doughnut-shaped polygon
library(sp)
library(maptools)
coords1 <- matrix(c(108, -54, -108, -54, -108, 54, 108, 54, 108, -54), ncol=2,
byrow=TRUE)
coords2 <- matrix(c(36, -18, -36, -18, -36, 18, 36, 18, 36, -18), ncol=2,
byrow=TRUE)
polySP <- SpatialPolygons(list(Polygons(list(Polygon(coords1, hole=FALSE),
Polygon(coords2, hole=TRUE)), ID=1)), proj4string=CRS("+proj=longlat
+datum=WGS84"))
#Convert sp-SpatialPolygons to PBS-PolySet with maptools function
polyPBS <- SpatialPolygons2PolySet(polySP)
#-> POS for SID == 2 are increasing and thus do not reflect PBS standards for a
polygon with a hole
PID SID POS X Y
1 1 1 1 108 -54
2 1 1 2 -108 -54
3 1 1 3 -108 54
4 1 1 4 108 54
5 1 1 5 108 -54
6 1 2 1 36 -18
7 1 2 2 36 18
8 1 2 3 -36 18
9 1 2 4 -36 -18
10 1 2 5 36 -18
I believe that it would require only a small change to
maptools/SpatialPolygons2PolySet to produce PolySet objects that meet the PBS
standards also for polygons with holes, i.e., replace the line
POS <- c(POS, 1:k)
with
POS <- if(slot(srs[[j]], "hole")) c(POS, k:1) else c(POS, 1:k)
inside the loops: for (i in 1:n) … for (j in 1:m) …
Sincerely,
Daniel Schlaepfer
My session infos:
sessionInfo()
R version 3.1.1 (2014-07-10)
Platform: x86_64-apple-darwin13.3.0 (64-bit)
locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
attached base packages:
[1] stats graphics grDevices
[4] utils datasets methods
[7] base
other attached packages:
[1] PBSmapping_2.67.60 maptools_0.8-30
[3] sp_1.0-15
loaded via a namespace (and not attached):
[1] foreign_0.8-61 grid_3.1.1
[3] lattice_0.20-29
-------------------------------------------------------
Daniel Schlaepfer, PhD
University of Wyoming
Laramie, WY 82071
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--
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 91 00
e-mail: roger.biv...@nhh.no
--
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 91 00
e-mail: roger.biv...@nhh.no
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