I have a script using the R package 'concaveman', but due to issues on the ubuntu platform that I need to run the code on I cannot install this package (it has taken me three days trying to solve it). So I am looking for an alternative.
I have a random set of points ranging from 3 to 1000s of points. I want to draw a convex hull/polygon around the outer most points (step after would be to rasterize). I have been trying to do it by converting the points to a raster, then use rastertopolygons, but in rare occasions points would be in the same raster cell resulting in only two unique points. Convaveman would make this into a linear polygon (which is what I want, without using concaveman). Here is the input data that would be problematic:
x <- structure(list(x = c(166.867, 166.867, 167.117, 166.8667), y = c(-20.6333,
-20.633, -20.833, -20.6333)), row.names = c(NA, -4L), class = c("tbl_df",
"tbl", "data.frame"))
This is what I tried not (with the error I get):
SP_pt <- SpatialPoints(x, proj4string=crs("+proj=longlat +ellps=WGS84 `+towgs84=0,0,0,0,0,0,0 +no_defs"))`
gridded(SP_pt) <- T
SP_pt_R <- raster(SP_pt)
SP_poly <- rasterToPolygons(SP_pt_R, dissolve = T)
suggested tolerance minimum: 0.333333
Error in points2grid(points, tolerance, round) :
dimension 1 : coordinate intervals are not constant
You can use chull in base R:
sp::Polygon(x[c(chull(x), chull(x)[1]), ])
#> An object of class "Polygon"
#> Slot "labpt":
#> [1] 166.95023 -20.69977
#>
#> Slot "area":
#> [1] 6.75e-05
#>
#> Slot "hole":
#> [1] FALSE
#>
#> Slot "ringDir":
#> [1] 1
#>
#> Slot "coords":
#> x y
#> [1,] 167.1170 -20.8330
#> [2,] 166.8667 -20.6333
#> [3,] 166.8670 -20.6330
#> [4,] 167.1170 -20.8330
Or if you want to use the sf package:
sf::st_polygon(list(as.matrix(x[c(chull(x), chull(x)[1]),])))
#> POLYGON ((167.117 -20.833, 166.8667 -20.6333, 166.867 -20.633, 167.117 -20.833))