pgirmess (version 1.6.9)

pave: Provide square polygons or their node coordinates along a segment

Description

Provide a user-defined cell grid of polygon squares (or square node points) along a segment. This can be used to define a sampling grid for spatial analysis.

Usage

pave(cordseg, yc, xc, fix.edge=NULL, ydown = TRUE, output = "list")

Arguments

cordseg

the segment coordinates. This can be a vector c(x1,y1,x2,y2), a 2 x 2 matrix or a data.frame (each line a coordinate)

yc

the number of segment divisions (y cells)

xc

the number of columns (x cells)

fix.edge

the edge length of a cell (user specified, default to NULL)

ydown

if TRUE (default) squares are computed decreasing y

output

a character string indicating which output is required. One of "list", "points" or "spdf". Partial match allowed

Value

According to the output selected, a list of polygon coordinates, a 2 column matrix with the nodes coordinates or a SpatialPolygonsDataFrame.

Details

The segment must have x1 < x2. If not, it is automatically reordered. When "spdf" is selected the output is an object of class SpatialPolygonsDataFrame. The value of the edge length of a cell can passed with the argument fix.edge. In this case, the coordinates of the segment right top are re-computed to adjust the cell edge to an user defined fixed value.

See Also

SpatialPolygonsDataFrame-class, readShapePoly, readOGR,over, diag2edge

Examples

# NOT RUN {
# segment sloping up
coord<-matrix(c(20,20,90,90),nr=2,byrow=TRUE)
plot(coord,type="n",xlim=c(0,100),ylim=c(0,110),asp=1)
lines(coord)
# point grids
gr<-pave(coord,20,4,output="points") # y decreasing
points(gr)
gr<-pave(coord,20,4,output="points",ydown=FALSE) # y increasing
points(gr,col="blue")
# square polygon grids
gr<-pave(coord,20,4) # y decreasing
for (i in 1:length(gr)) polygon(gr[[i]])
gr<-pave(coord,20,4,ydown=FALSE) # y increasing
for (i in 1:length(gr)) polygon(gr[[i]],border="blue")

# segment sloping down
coord<-matrix(c(20,90,90,20),nr=2,byrow=TRUE)
plot(coord,type="n",xlim=c(0,100),ylim=c(0,110),asp=1)
lines(coord)

# point grids
gr<-pave(coord,20,4,output="points")  # y decreasing
points(gr)
gr<-pave(coord,20,4,output="points",ydown=FALSE) # y increasing
points(gr,col="blue")

# fixed edge
plot(coord,type="n",xlim=c(0,100),ylim=c(0,110),asp=1)
lines(coord)
gr<-pave(coord,20,4,fix.edge=4,output="points")
points(gr,col="blue")

plot(coord,type="n",xlim=c(0,100),ylim=c(0,110),asp=1)
lines(coord)
gr<-pave(coord,20,4,fix.edge=5.5,output="points")
points(gr,col="red")

# square polygon grids
coord<-matrix(c(20,90,90,20),nr=2,byrow=TRUE)
plot(coord,type="n",xlim=c(0,100),ylim=c(0,110),asp=1)
lines(coord,lwd=2)
gr<-pave(coord,20,4)# y decreasing
for (i in 1:length(gr)) polygon(gr[[i]]) 
gr<-pave(coord,20,4,ydown=FALSE) # y increasing
for (i in 1:length(gr)) polygon(gr[[i]],border="blue")

# }
# NOT RUN {
# Writing a polygon shapefile
gr<-pave(coord,20,4,output="spdf") # y decreasing
library(maptools)
writePolyShape(gr, "myshapefilename")
# }
# NOT RUN {
# }