[R-sig-Geo] Making an hexagonal grid using spsample

[Timothée Giraud]

Hi,

I understand you find a solution via hextess from spatstat.

However, this is a solution with spsample from sp.

Actually, the cellsize argument of spsample defines the distance between 
the center of consecutives hexagons.
So it is the length of 2 medians of one of the 6 equilateral triangles 
composing the hexagon.

You can obtain the correct cellsize with:
- the formula that calculates the median length for a given equilateral 
triangle length size,
- the formula that calculate the area of an hexagon with a given side 
length.


library(sp)
data(meuse.grid)
gridded(meuse.grid) = ~x+y
plot(meuse.grid)

# targeted area in meters
A <- 10000
# Corresponding cellsize :
CS <- 2 * sqrt(A/((3*sqrt(3)/2))) * sqrt(3)/2

# hexagons
HexPts <-spsample(x = meuse.grid, type = "hexagonal", cellsize = CS)
HexPols <- HexPoints2SpatialPolygons(HexPts)

plot(HexPols, add=TRUE)

# check
rgeos::gArea(HexPols, byid = T)[1:10]




Since you asked me about getGridLayer via PM, this function of the 
cartography package uses spsample with its cellsize argument, maybe I 
should add a "targeted area" argument...