aggRasterPoly: function to accumulate or calculate average polygon values...
In nickbond/catchstats: Tools for manipulating nested catchment datasets

Description Usage Arguments Value Note Examples

function to accumulate or calculate average polygon values within a set of upstream catchment polygons.

aggRasterPoly(
  shpfile,
  rast = NULL,
  catid_col,
  nextds_col,
  nextds2_col = NULL,
  catarea_col,
  reporting_cats = NULL,
  start = 1,
  end = nrow(shpfile),
  loc_cat_df = NULL,
  fun = NULL
)

`shpfile`	The shapefile to be used to intersect with the raster layers (optional)
`rast`	The raster layer(s) to be intersected
`catid_col`	The field in the shapefile with the catchment ID values (e.g. 'site', 'SEGMENTNO')
`nextds_col`	The field in the shapefile indicating the next downstream catchment. Required for identifying catchments to aggregate.
`nextds2_col`	A second field in the shapefile indicating altnerative next downstream catchment for anabranches. Required for identifying catchments to aggregate.
`catarea_col`	The field containing the catchment areas. This is used for calculating the relative contributing area for weighting values when fun #' ='average'.
`reporting_cats`	A vector of 'sites' etc. to calculate values for. Otherwise defaults to all fields in catid_col. See optional start and end for #'alternative subsetting approach.
`start`	the first polygon in the shapefile to be used for intersection Defaults to a value of 1 (the first row).
`end`	The last polygon in the shapfile to be intersected.
`loc_cat_df`	A dataframe containing values for individual subcatchments to aggreagte - produced by running aggRasterPoly. If provided, there is no need to specify the raster layer, although the shapefile is still required to produce the catchment hierarchy.
`fun`	The aggregation function - 'average', 'accumulate', 'area_sum'. The former would typically be used for variables such as rainfall, whereas number of survey sites might be summed ('accumulate'), while runoff might be accumulated as runoff volume (mm/km^2 * catchment area) by taking into account sub-catchment areas using 'area_sum'.

a dataframe of area-weighted or summed values derived from all sub-catchments contributing to each catchment.

The function can be used to extract values from a raster layer (or stack) or be applied ot existing dataframe of polygon values. For extraction the shapefile and raster stack must be projected in the same projection.