maptools: nowrapRecenter – R documentation

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nowrapRecenter

Break polygons at meridian for recentering

Description

When recentering a world map, say to change an "Atlantic" view with longitude range -180 to 180, to a "Pacific" view, with longitude range 0 to 360, polygons crossed by the new offset, here 0/360, need to be clipped into left and right sub.polygons to avoid horizontal scratches across the map. The nowrapSpatialPolygons function performs this operation using polygon intersection, and nowrapRecenter recenters the output SpatialPolygons object.

Usage

nowrapRecenter(obj, offset = 0, eps = rep(.Machine$double.eps^(1/2.5), 2),
 avoidGEOS = FALSE)
nowrapSpatialPolygons(obj, offset = 0, eps=rep(.Machine$double.eps^(1/2.5), 2),
 avoidGEOS = FALSE)

Arguments

`obj`	A SpatialPolygons object
`offset`	offset from the Greenwich meridian
`eps`	vector of two (left and right) fuzz factors to retract the ring from the offset (2.5 root to accommodate rgeos precision rules)
`avoidGEOS`	default FALSE; use polyclip or gpclib code even if rgeos is available

Value

A SpatialPolygons object

Author(s)

Roger Bivand

Examples

run <- FALSE
if (require(maps)) run <- TRUE
## Not run: 
if (run) {
world <- map("world", fill=TRUE, col="transparent", plot=FALSE)
worldSpP <- map2SpatialPolygons(world, world$names, CRS("+proj=longlat +ellps=WGS84"))
worldSpP <- worldSpP[-grep("Antarctica", row.names(worldSpP)),]
# incomplete polygons
worldSpP <- worldSpP[-grep("Ghana", row.names(worldSpP)),]
# self-intersection mouth of Volta
worldSpP <- worldSpP[-grep("UK:Great Britain", row.names(worldSpP)),]
# self-intersection Humber estuary
worldSpPr <- recenter(worldSpP)
plot(worldSpPr)
title("Pacific view without polygon splitting")
}
if (run) {
worldSpPnr <- nowrapRecenter(worldSpP)
plot(worldSpPnr)
title("Pacific view with polygon splitting")
}

## End(Not run)
if (!rgeosStatus()) run <- FALSE
if (run) {
crds <- matrix(c(-1, 1, 1, -1, 50, 50, 52, 52), ncol=2)
rcrds <- rbind(crds, crds[1,])
SR <- SpatialPolygons(list(Polygons(list(Polygon(rcrds)), ID="r1")),
 proj4string=CRS("+proj=longlat +ellps=WGS84"))
bbox(SR)
}
if (run) {
SRr <- recenter(SR)
bbox(SRr)
}
if (run) {
SRnr <- nowrapRecenter(SR)
bbox(SRnr)
}

maptools

Tools for Handling Spatial Objects

v1.1-1

GPL (>= 2)

Authors

Roger Bivand [cre, aut] (<https://orcid.org/0000-0003-2392-6140>), Nicholas Lewin-Koh [aut], Edzer Pebesma [ctb], Eric Archer [ctb], Adrian Baddeley [ctb], Nick Bearman [ctb], Hans-Jörg Bibiko [ctb], Steven Brey [ctb], Jonathan Callahan [ctb], German Carrillo [ctb], Stéphane Dray [ctb], David Forrest [ctb], Michael Friendly [ctb], Patrick Giraudoux [ctb], Duncan Golicher [ctb], Virgilio Gómez Rubio [ctb], Patrick Hausmann [ctb], Karl Ove Hufthammer [ctb], Thomas Jagger [ctb], Kent Johnson [ctb], Matthew Lewis [ctb] (<https://orcid.org/0000-0003-2244-4078>), Sebastian Luque [ctb], Don MacQueen [ctb], Andrew Niccolai [ctb], Edzer Pebesma [ctb], Oscar Perpiñán Lamigueiro [ctb], Ethan Plunkett [ctb], Ege Rubak [ctb] (<https://orcid.org/0000-0002-6675-533X>), Tom Short [ctb], Greg Snow [ctb], Ben Stabler [ctb], Murray Stokely [ctb], Rolf Turner [ctb]

Initial release

2021-03-14