Function to select nearest community to a given sampling point (usually the centroid of a square grid for CSAS or of a hexagonal grid for S3M) based on a nearest neighbour algorithm using Euclidean calculations

get_nn(data, x1, y1, query, x2, y2, n, duplicate = FALSE)

Arguments

data	An input data frame or matrix containing longitude and latitude coordinates of village locations from which to find nearest neighbour
x1	A character value specifying the variable name in `data` containing the longitude coordinates
y1	A character value specifying the variable name in `data` containing the latitude coordinates
query	an object of class `SpatialPoints` containing sampling point locations. This is usually the output from applying `spsample()` function from package `gstat` to create an even spatial sample across the entire sampling area
x2	A character value specifying the variable name in `query` containing the longitude coordinates
y2	A character value specifying the variable name in `query` containing the latitude coordinates
n	A numeric value speciyfing the maximum number of nearest neighbours to search for
duplicate	Logical. Specify if duplicate selected villages are to be kept or discarded. Default is FALSE (discard).

Value

A subset data frame of data of selected villages/communities nearest to the sampling points with a new variable d indicating the distance of the village/community to the sampling point (in coordinate units). If duplicate is TRUE, the result has number of rows equal to nrow(query)

Examples

# Use get_nn() with test sampling points in Sennar to find 3 nearest communities
# from the sampling points
sennar <- subset(sudan01, STATE == "Sennar")
samp.points <- sp::spsample(sennar, type = "hexagonal", n = 10)
#> Warning: Discarded datum WGS_1984 in CRS definition,
#>  but +towgs84= values preserved
#> Warning: Discarded datum WGS_1984 in CRS definition,
#>  but +towgs84= values preserved
#> Warning: Discarded datum WGS_1984 in CRS definition,
#>  but +towgs84= values preserved
#> Warning: CRS object has comment, which is lost in output
get_nn(data = sennar_villages, x1 = "x", y1 = "y",
       query = samp.points, x2 = "x", y2 = "y",
       n = 3)
#>      id        x        y              village     locality          d
#> 732 933 33.75706 12.41561 Arab AlBalf (Kockry)    Abu Hijar 0.12172316
#> 244 244 34.79008 12.82597       Um Bagara Garb    Al Dindir 0.56646537
#> 520 520 33.60339 13.17444         Al Kharasabi        Sinja 0.17244608
#> 100 100 34.24214 13.01453              Kamrab     Al Dindir 0.03399852
#> 179 179 34.86331 13.02667             Um Bagaa    Al Dindir 0.01658150
#> 565 565 33.89186 13.57608              Kanbo 7 Sharg Sennar 0.01826824
#> 58   58 34.03142 12.47114                 Tozi    Abu Hijar 0.15822616
#> 126 126 34.79900 12.84908     Om Bagara Sharig    Al Dindir 0.57625866
#> 317 317 33.63758 13.21264           wd salmaan      AlSooki 0.22078325
#> 95   95 34.27258 13.00028           Al Fereesh    Al Dindir 0.06543542
#> 564 564 33.88842 13.55625          Al Mansoora Sharg Sennar 0.03224762
#> 63   63 33.70803 12.59786             Alsahbaa    Abu Hijar 0.23246016
#> 124 124 34.77686 12.85164             Om Sagit    Al Dindir 0.59375885
#> 528 528 33.69922 13.20789 Dar Alsalam Alkurtan        Sinja 0.24909832
#> 101 101 34.23367 13.07678             Khameesa    Al Dindir 0.06949234
#> 563 563 33.83750 13.56875  Mabriika Wa Barakat Sharg Sennar 0.04296518