Spatial - Clip (intersect) polygon vector layer with polygon vector layer.

Wrapper for sf::st_intersection, to clip (intersect) polygon vector layer with another polygon vector layer.

Usage

spClipPoly(
  polyv,
  polyv_dsn = NULL,
  clippolyv,
  clippolyv_dsn = NULL,
  clippolyv.filter = NULL,
  buffdist = NULL,
  validate = FALSE,
  showext = FALSE,
  areacalc = FALSE,
  areaunits = "ACRES",
  nolonglat = TRUE,
  exportsp = FALSE,
  savedata_opts = NULL
)

Arguments

polyv: sf R object or String. Polygon data to clip. Can be a spatial polygon object, full pathname to a shapefile, or name of a layer within a database.
polyv_dsn: String. Data source name (dsn; e.g., sqlite or shapefile pathname) of layer to clip. The dsn varies by driver. See gdal OGR vector formats (https://www.gdal.org/ogr_formats.html). Optional if polyv is sf object.
clippolyv: SpatialPolygons class R object or String. Name of the polygon spatial layer to use for clipping.
clippolyv_dsn: String. Data source name (dsn; i.e., pathname or database name) of clippolyv_layer. The dsn varies by driver. See gdal OGR vector formats (https://www.gdal.org/ogr_formats.html). Optional if clippolyv_layer is an R object.
clippolyv.filter: String. Filter to subset clippolyv spatial layer.
buffdist: Number. The distance to buffer the polygon before clipping. Uses sf::st_buffer. The distance is based on units of polygon, st_crs(x)$units.
validate: Logical. If TRUE, validates polyv and clippolyv before clipping. Uses sf::st_make_valid with default parameters (geos_method='valid_structure', geos_keep_collapsed=FALSE).
showext: Logical. If TRUE, layer extents are displayed in plot window.
areacalc: Logical. If TRUE, calculate area of clipped polygons and append to attribute table (See details).
areaunits: String. If TRUE, calculate area of clipped polygons and append to attribute table ("ACRES", "HECTARES", "SQKM"). If NULL, units of polyv.
nolonglat: Logical. If TRUE, and both layer's coordinate system is long/lat, the layers are converted to a projected CRS before clipping.
exportsp: Logical. If TRUE, the spatial clipped object is exported to outfolder (see spExportSpatial for details).
savedata_opts: List. See help(savedata_options()) for a list of options for saving data. If out_layer = NULL, default = 'polyclip'.

Value

sf object of clipped polygon. If polyv and clippolyv have different projections, the projection of returned object will have the same projection as polyv (See note about on-the-fly projection conversion).

If exportsp=TRUE, the sf object will be written to outfolder (See note).

Details

The sf::st_intersection function is used to clip polygons.

areacalc
If areacalc = TRUE and the clipped spatial object is not in a projected coordinate system (i.e., longlat), the object will be reprojected to the Albers Equal Area projection before area is calculated.

Note

On-the-fly projection conversion
The spTransform (sf) method is used for on-the-fly map projection conversion and datum transformation using PROJ.4 arguments. Datum transformation only occurs if the +datum tag is present in the both the from and to PROJ.4 strings. The +towgs84 tag is used when no datum transformation is needed. PROJ.4 transformations assume NAD83 and WGS84 are identical unless other transformation parameters are specified. Be aware, providing inaccurate or incomplete CRS information may lead to erroneous data shifts when reprojecting. See spTransform help documentation for more details.

ESRI Shapefile Driver
If exportsp=TRUE:
The st_write (sf) function is called. If out_fmt="shp", the ESRI Shapefile driver truncates variable names to 10 characters or less. Variable names are changed before export using an internal function (trunc10shp). If sf object has more than 1 record, it will be returned but not exported.

Author

Tracey S. Frescino