geoR (version 1.9-4)

subarea: Selects a Subarea from a Geodata Object

Description

Selects elements of a geodata object wich are within a rectangular (sub)area

Usage

subarea(geodata, xlim, ylim, ...)

Value

Returns an geodata object, subsetting of the original one provided.

Arguments

geodata

an object of the class geodata as defined in as.geodata.

xlim

optional, a vector with selected range of the x-coordinates.

ylim

optional, a vector with selected range of the y-coordinates.

...

further arguments to be passed to zoom.coords.

Author

Paulo Justiniano Ribeiro Jr. ,
Peter J. Diggle .

Details

The function copies the original geodata object and selects values of $coords, $data, $borders, $covariate and $units.m which lies within the selected sub-area. Remaining components of the geodata objects are untouched.

If xlim and/or ylim are not provided the function prompts the user to click 2 points defining an retangle defining the subarea on a existing plot.

See Also

zoom.coords, locator

Examples

foo <- matrix(c(4,6,6,4,2,2,4,4), nc=2)
foo1 <- zoom.coords(foo, 2)
foo1
foo2 <- coords2coords(foo, c(6,10), c(6,10))
foo2
plot(1:10, 1:10, type="n")
polygon(foo)
polygon(foo1, lty=2)
polygon(foo2, lwd=2)
arrows(foo[,1], foo[,2],foo1[,1],foo1[,2], lty=2)
arrows(foo[,1], foo[,2],foo2[,1],foo2[,2])
legend("topleft", c("foo", "foo1 (zoom.coords)", "foo2 (coords2coords)"), 
       lty=c(1,2,1), lwd=c(1,1,2))

## "zooming" part of The Gambia map
gb <- gambia.borders/1000
gd <- gambia[,1:2]/1000
plot(gb, ty="l", asp=1, xlab="W-E (kilometres)", ylab="N-S (kilometres)")
points(gd, pch=19, cex=0.5)
r1b <- gb[gb[,1] < 420,]
rc1 <- rect.coords(r1b, lty=2)

r1bn <- zoom.coords(r1b, 1.8, xoff=90, yoff=-90)
rc2 <- rect.coords(r1bn, xz=1.05)
segments(rc1[c(1,3),1],rc1[c(1,3),2],rc2[c(1,3),1],rc2[c(1,3),2], lty=3)

lines(r1bn)
r1d <- gd[gd[,1] < 420,]
r1dn <- zoom.coords(r1d, 1.7, xlim.o=range(r1b[,1],na.rm=TRUE), ylim.o=range(r1b[,2], na.rm=TRUE), 
                    xoff=90, yoff=-90)
points(r1dn, pch=19, cex=0.5)
text(450,1340, "Western Region", cex=1.5)

#if(require(geoRglm)){
#data(rongelap)
#points(rongelap)
## zooming the western area
#rongwest <- subarea(rongelap, xlim=c(-6300, -4800))
#points(rongwest)
## now zooming in the same plot
#points(rongelap)
#rongwest.z <- zoom.coords(rongwest, xzoom=3, xoff=2000, yoff=3000)
#points(rongwest.z, add=TRUE)
#rect.coords(rongwest$sub, quiet=TRUE)
#rect.coords(rongwest.z$sub, quiet=TRUE)
#}