Envelope of Geometry

Function calculates the rectangular bounding box for the given geometry

gEnvelope(spgeom, byid=FALSE, id = NULL)

Arguments

spgeom

sp object as defined in package sp

byid

Logical determining if the function should be applied across subgeometries (TRUE) or the entire object (FALSE)

id

Character vector defining id labels for the resulting geometries, if unspecified returned geometries will be labeled based on their parent geometries' labels.

Details

Returns the rectangular bounding box as a SpatialPolygons object. If spgeom is a degenerate case (horizontal/vertical line, single point) then the function may return an object with lower dimension (SpatialLines or SpatialPoints) or an invalid polygon.

Author

Roger Bivand & Colin Rundel

Examples

x = readWKT(paste("POLYGON((0 40,10 50,0 60,40 60,40 100,50 90,60 100,60",
 "60,100 60,90 50,100 40,60 40,60 0,50 10,40 0,40 40,0 40))"))
env = gEnvelope(x)

plot(x,col='blue',border='blue')
plot(env,add=TRUE)


#Degenerate Cases
gEnvelope(readWKT("POINT(1 1)")) #returns SpatialPoints
#> SpatialPoints:
#>   x y
#> 1 1 1
#> Coordinate Reference System (CRS) arguments: NA 
gEnvelope(readWKT("LINESTRING(1 1,1 2)")) #invalid polygon
#> An object of class "SpatialPolygons"
#> Slot "polygons":
#> [[1]]
#> An object of class "Polygons"
#> Slot "Polygons":
#> [[1]]
#> An object of class "Polygon"
#> Slot "labpt":
#> [1] 1.0 1.5
#> 
#> Slot "area":
#> [1] 0
#> 
#> Slot "hole":
#> [1] FALSE
#> 
#> Slot "ringDir":
#> [1] 1
#> 
#> Slot "coords":
#>      x y
#> [1,] 1 1
#> [2,] 1 2
#> [3,] 1 2
#> [4,] 1 1
#> [5,] 1 1
#> 
#> 
#> 
#> Slot "plotOrder":
#> [1] 1
#> 
#> Slot "labpt":
#> [1] 1.0 1.5
#> 
#> Slot "ID":
#> [1] "1"
#> 
#> Slot "area":
#> [1] 0
#> 
#> 
#> 
#> Slot "plotOrder":
#> [1] 1
#> 
#> Slot "bbox":
#>   min max
#> x   1   1
#> y   1   2
#> 
#> Slot "proj4string":
#> Coordinate Reference System:
#> Deprecated Proj.4 representation: NA 
#> 
gEnvelope(readWKT("LINESTRING(1 1,2 1)")) #invalid polygon
#> An object of class "SpatialPolygons"
#> Slot "polygons":
#> [[1]]
#> An object of class "Polygons"
#> Slot "Polygons":
#> [[1]]
#> An object of class "Polygon"
#> Slot "labpt":
#> [1] 1.5 1.0
#> 
#> Slot "area":
#> [1] 0
#> 
#> Slot "hole":
#> [1] FALSE
#> 
#> Slot "ringDir":
#> [1] 1
#> 
#> Slot "coords":
#>      x y
#> [1,] 1 1
#> [2,] 1 1
#> [3,] 2 1
#> [4,] 2 1
#> [5,] 1 1
#> 
#> 
#> 
#> Slot "plotOrder":
#> [1] 1
#> 
#> Slot "labpt":
#> [1] 1.5 1.0
#> 
#> Slot "ID":
#> [1] "1"
#> 
#> Slot "area":
#> [1] 0
#> 
#> 
#> 
#> Slot "plotOrder":
#> [1] 1
#> 
#> Slot "bbox":
#>   min max
#> x   1   2
#> y   1   1
#> 
#> Slot "proj4string":
#> Coordinate Reference System:
#> Deprecated Proj.4 representation: NA 
#>