[R-sig-Geo] distances values from a point exhibit a hexagon-like distribution

[Robert J. Hijmans]

Mike,

You are using a more recent version of raster. The "projs" argument in
raster() was, for consistency, replaced by "crs", and gridDistance()
now requires two more arguments, originValue and omitValue.
In Roman's example, this:

rst.grid <- gridDistance(rst.cover)

should be replaced by:

rst.grid <- gridDistance(rst.cover, 1, 0)

Best, Robert

On Tue, Jun 22, 2010 at 1:37 AM, Michael Sumner <mdsumner at gmail.com> wrote:
> Sorry, but it still doesn't work for me. I'm surprised you could get
> passed the first line, since "projs" is not an argument to raster -
> it's not necessary for your example to have that set though, so I
> ignore it.
>
> I had to install igraph package as well, but still this fails at the
> gridDistance line. Can you let us know your OS, R and package versions
> for raster, sp, and igraph?  Use sessionInfo()  please.
>
> library(raster)
> library(sp)
> library(igraph)
>
> rst <- raster(nrow = 200, ncol = 200, xmn = -100, xmx = 100, ymn =
> -100, ymx = 100)
> sample.matrix <- t(matrix(c(50,-50, 50,50, -50,50, -50,-50), 2, 4))
> sample.matrix <- rbind(sample.matrix, sample.matrix[1,])
> sq.polygon <- SpatialPolygons(list(Polygons(list(Polygon(sample.matrix)),
> ID = "effect_dist")))
> rst[] <- runif(ncell(rst))
> xy <- matrix(c(0,0), 1, 2)
>
> rst.poly <- polygonsToRaster(sq.polygon, rst)
> rst.lines <- linesToRaster(sq.polygon, rst)
>
> rst.lines[rst.lines > 0] <- 0
>
> rst.point <- pointsToRaster(rst, xy)
>
> rst.cover <- cover(rst.point, rst.lines)
>
> ## fails at this line
> rst.grid <- gridDistance(rst.cover)
> rst.grid[!is.na(rst.lines)] <- NA
> plot(rst.grid)
>
> sessionInfo()
>
> R version 2.11.1 (2010-05-31)
> x86_64-pc-mingw32
>
> locale:
> [1] LC_COLLATE=English_Australia.1252  LC_CTYPE=English_Australia.1252
>   LC_MONETARY=English_Australia.1252
> [4] LC_NUMERIC=C                       LC_TIME=English_Australia.1252
>
> attached base packages:
> [1] stats     graphics  grDevices utils     datasets  methods   base
>
> other attached packages:
> [1] igraph_0.5.3 raster_1.1.7 sp_0.9-64
>
> loaded via a namespace (and not attached):
> [1] grid_2.11.1    lattice_0.18-8 tools_2.11.1
>
>
> On Tue, Jun 22, 2010 at 6:28 PM, Roman Luštrik <roman.lustrik at gmail.com> wrote:
>> Thank you Michael for taking interest in my problem. Here is the code that
>> should work. The only difference is that here, for a polygon, I use a square
>> instead of a circle (no biggie). I suspect gridDistance may have something
>> to do with the "hexagon".
>>
>> library(raster)
>> library(sp)
>> rst <- raster(nrow = 200, ncol = 200, xmn = -100, xmx = 100, ymn = -100, ymx
>> = 100, projs = "+proj=NA")
>> sample.matrix <- t(matrix(c(50,-50, 50,50, -50,50, -50,-50), 2, 4))
>> sample.matrix <- rbind(sample.matrix, sample.matrix[1,])
>> sq.polygon <- SpatialPolygons(list(Polygons(list(Polygon(sample.matrix)), ID
>> = "effect_dist")))
>> rst[] <- runif(ncell(rst))
>> xy <- matrix(c(0,0), 1, 2)
>>
>> rst.poly <- polygonsToRaster(sq.polygon, rst)
>> rst.lines <- linesToRaster(sq.polygon, rst)
>>
>> rst.lines[rst.lines > 0] <- 0
>> rst.point <- pointsToRaster(rst, xy)
>>
>> rst.cover <- cover(rst.point, rst.lines)
>> rst.grid <- gridDistance(rst.cover)
>> rst.grid[!is.na(rst.lines)] <- NA
>> plot(rst.grid)
>>
>>
>> Cheers,
>> Roman
>>
>>
>>
>>
>> On Tue, Jun 22, 2010 at 9:55 AM, Michael Sumner <mdsumner at gmail.com> wrote:
>>
>>> Could you please provide a reproducible example with useable code?
>>>
>>> Cheers, Mike.
>>>
>>> On Tue, Jun 22, 2010 at 5:36 PM, Roman Luštrik <roman.lustrik at gmail.com>
>>> wrote:
>>> > Can someone explain to me why values of distances from a point are not in
>>> a
>>> > uniform, circle-like fashion, but rather form a hexagon shape (see
>>> > image<http://imagepaste.nullnetwork.net/viewimage.php?id=1075>)?
>>> > Here is the code I'm using to produce this plot (kudos to
>>> > Robert<
>>> http://r-sig-geo.2731867.n2.nabble.com/assigning-raster-cell-values-based-on-predefined-criteria-td4929775.html#a4929775
>>> >).
>>> > Raster projection is "+projs = NA".
>>> >
>>> > rst.poly <- polygonsToRaster(circle.polygon, rst) #circle.polygon is the
>>> > polygon I'm overlaying, rst is the raster
>>> > rst.lines <- linesToRaster(circle.polygon, rst)
>>> > rst.lines[rst.lines > 0] <- 0
>>> > rst.point <- pointsToRaster(rst, xy[[i]][j,]) #xy is the point from where
>>> > the distances are calculated
>>> > rst.cover <- cover(rst.point, rst.lines)
>>> > rst.grid <- gridDistance(rst.cover)
>>> > rst.grid[!is.na(rst.lines)] <- NA
>>> > plot(rst.grid)
>>> >
>>> >
>>> > Cheers,
>>> > Roman
>>> >
>>> >
>>> > --
>>> > In God we trust, all others bring data.
>>> >
>>> >        [[alternative HTML version deleted]]
>>> >
>>> > _______________________________________________
>>> > R-sig-Geo mailing list
>>> > R-sig-Geo at stat.math.ethz.ch
>>> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>> >
>>>
>>
>>
>>
>> --
>> In God we trust, all others bring data.
>>
>>
>>
>> --
>> In God we trust, all others bring data.
>>
>>        [[alternative HTML version deleted]]
>>
>>
>> _______________________________________________
>> R-sig-Geo mailing list
>> R-sig-Geo at stat.math.ethz.ch
>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>
>>
>
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