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

[Manuel Spínola]

Thank you very much Timothée.

That works.

Manuel

2017-03-06 9:42 GMT-06:00 Timothée Giraud <timothee.giraud at cnrs.fr>:

> 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...
>
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>



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*Manuel Spínola, Ph.D.*
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