Split SpatialLines components at offset

When recentering a world map, most often from the "Atlantic" view with longitudes with range -180 to 180, to the "pacific" view with longitudes with range 0 to 360, lines crossing the offset (0 for this conversion) get stretched horizonally. This function breaks Line objects at the offset (usually Greenwich), inserting a very small gap, and reassembling the Line objects created as Lines. The rgeos package is required to use this function.

nowrapSpatialLines(obj, offset = 0, eps = rep(.Machine$double.eps^(1/2.5), 2))

Arguments

obj

A Spatial Lines object

offset

default 0, untried for other values

eps

vector of two fuzz values, both default 2.5 root of double.eps

Value

A Spatial Lines object

Author

Roger Bivand

Examples

Sl <- SpatialLines(list(Lines(list(Line(cbind(sin(seq(-4,4,0.4)),
 seq(1,21,1)))), "1")), proj4string=CRS("+proj=longlat +ellps=WGS84"))
summary(Sl)
#> Object of class SpatialLines
#> Coordinates:
#>          min        max
#> x -0.9995736  0.9995736
#> y  1.0000000 21.0000000
#> Is projected: FALSE 
#> proj4string : [+proj=longlat +ellps=WGS84 +no_defs]
if (require(rgeos)) {
nwSL <- nowrapSpatialLines(Sl)
summary(nwSL)
if(require(maps)) {
worldmap <- map("world", plot=FALSE)
worldmapLines <- map2SpatialLines(worldmap, proj4string=CRS("+proj=longlat +datum=WGS84"))
bbox(worldmapLines)
t0 <- nowrapSpatialLines(worldmapLines, offset=180)
bbox(t0)
}
}
#> Warning: GEOS support is provided by the sf and terra packages among others
#> Warning: GEOS support is provided by the sf and terra packages among others
#> Warning: GEOS support is provided by the sf and terra packages among others
#> Warning: GEOS support is provided by the sf and terra packages among others
#> Warning: GEOS support is provided by the sf and terra packages among others
#> Warning: GEOS support is provided by the sf and terra packages among others
#> Warning: GEOS support is provided by the sf and terra packages among others
#> Warning: GEOS support is provided by the sf and terra packages among others
#> Warning: GEOS support is provided by the sf and terra packages among others
#> Warning: GEOS support is provided by the sf and terra packages among others
#> Warning: GEOS support is provided by the sf and terra packages among others
#> Warning: GEOS support is provided by the sf and terra packages among others
#> Warning: GEOS support is provided by the sf and terra packages among others
#> Warning: GEOS support is provided by the sf and terra packages among others
#>          min       max
#> x -180.00000 190.27084
#> y  -85.19218  83.59961