UpslopeDEM: Calculate upslope polygon from DEM
In ECCC-MSC/Basin-Delineation: Finds upstream area and upstream stations

Create a drainage basin shapefile using a DEM and a 'pour point'. The polygon is

UpslopeDEM(point, DEM_path, DEM_source = "NTS", saga_env, outdir,
  pointbuffer = 50, clip_size = 50000, projected.CRS, iterate_to = 150,
  iterate_incr = 50, iterate_thres = 0.4, method = "D8",
  upstr_threshold = 35000, ...)

`point`	a SpatialPointsDataFrame corresponding to a hydrometric station. Must be in same coordinates system as DEM and coordinate system must be projected (not lat/long). Must have longitude and latitude attributes.
`DEM_path`	One of: (1) a file path to a directory containing DEM files either in the the format n tiles will be downloaded (if DEM_source='CDEM', 'CDED' etc.), (2) a file path to a dem file in SAGA format. The DEM should be in a projected coordinate system and the coordinatesystem should match that of the point (e.g. Canada Albers Conformal Conic) @param clip_size How big (in m) a clip should be generated from the original DEM (too big doesn't work and is slower) @param projected.CRS character vector (proj4) specifying "working" CRS in which area and distance calculations are to be done
`DEM_source`	character, one of: c('CDED', 'NED', 'CDEM, CDSM', 'SHEDS'). Ignored if a DEM file is supplied to DEM_path
`saga_env`	an rsaga environment object
`outdir`	Directory to output final upslope shapefile
`pointbuffer`	numeric, how much should the point be buffered (calculates upslope basin of buffered area)
`iterate_to`	numeric, if greater than pointbuffer, checks that the calculated upslope area is at least 0.5 sq. km larger than the
`iterate_incr`	numeric, by how much should the buffer be grown each iteration (ignored if iterate_to is equal to pointbuffer) @param iterate_thres numeric, how many square kilometers difference between the calculated area and initial point buffer should be required to trigger another iteration (ignored if iterate_to is equal to pointbuffer)
`method`	character, one of ('D8', 'DINF'), specifying the hydrological pathing model
`upstr_threshold`	integer, number of upstream cells required to initiate channel growth. A smaller number will yield more channels and will snap to smaller streams. Larger numbers will produce only major channel branches. For a 50k DEM, numbers between 20,000 and 50,000 are appropriate to reproduce the main channel network without many small branches. @return A list containing diagnostic information and and a character string naming the recently created upstream area polygon
`...`	optional arguments to rsaga.geoprocessor including 'verbose' (toggles SAGA console output)