Return boundary coordinates for cells intersecting a shapefile

Returns the coordinates constituting the boundary of a set of cells which intersect or are contained by a polygon (or polygons) specified in a shapefile. Note that grid cells are also generated for holes in the shapefile's polygon(s).

Note that coordinates in the shapefile must be rounded to check polygon intersections. Currently this round preserves eight decimal digits of precision.

The eighth decimal place is worth up to 1.1 mm of precision: this is good for charting the motions of tectonic plates and the movements of volcanoes. Permanent, corrected, constantly-running GPS base stations might be able to achieve this level of accuracy.

In other words: you should be just fine with this level of precision.

Usage

dgshptogrid(dggs, shpfname, cellsize = 0.1, ...)

Arguments

dggs: A dggs object from dgconstruct()
shpfname: Either a sf data frame or the file name of the shapefile. Filename should end with '.shp'.
cellsize: Distance, in degrees, between the sample points used to generate the grid. Small values yield long generation times while large values may omit cells.
...: Further arguments passed to dgcellstogrid.

Value

Returns an sf object. If !is.na(savegrid), returns a filename.

Examples

library(dggridR)

dggs <- dgconstruct(spacing=25, metric=FALSE, resround='nearest')
#> Resolution: 9, Area (mi^2): 1610.22194501, Spacing (mi): 31.2406017233859, CLS (mi): 35.6922386250717
south_africa_grid <- dgshptogrid(dggs,dg_shpfname_south_africa())
#> Reading layer `ZAF_adm0' from data source 
#>   `/home/runner/work/_temp/Library/dggridR/extdata' using driver `ESRI Shapefile'
#> Simple feature collection with 1 feature and 1 field
#> Geometry type: MULTIPOLYGON
#> Dimension:     XY
#> Bounding box:  xmin: 16.45802 ymin: -46.93639 xmax: 37.87945 ymax: -22.14108
#> CRS:           NA
head(south_africa_grid)
#> Simple feature collection with 6 features and 1 field
#> Geometry type: POLYGON
#> Dimension:     XY
#> Bounding box:  xmin: 16.05806 ymin: -47.3298 xmax: 20.26694 ymax: -46.41935
#> Geodetic CRS:  WGS 84
#>   seqnum                       geometry
#> 1  57929 POLYGON ((16.69582 -46.4532...
#> 2  58092 POLYGON ((17.3761 -46.73251...
#> 3  58173 POLYGON ((18.00873 -46.5391...
#> 4  58336 POLYGON ((18.69427 -46.8076...
#> 5  58417 POLYGON ((19.3212 -46.60332...
#> 6  58580 POLYGON ((20.01159 -46.8617...