vrcd: variable-resolution costDistance

In matthewkling/windscape: Landscape connectivity by wind

variable-resolution costDistance

Description

Increasing the spatial resolution of a wind data set (e.g. by interpolation using downscale) can greatly improve wind connectivity estimates among nearby sites, but can make it computationally impossible to model connectivity over large geographic regions, a trade-off that presents problems for studies that include both nearby and distant site pairs. This function gets around this issue with a hybrid approach, using a broad-scale coarse-resolution wind grid to model wind cost-distance among distant sites, and a separate local-scale high-resolution interpolated grid to model connectivity between each pair of nearby sites.

Usage

vrcd(
  rose,
  ll,
  threshold_km = 30,
  pad = 1,
  max_nodes = 1e+06,
  direction = "downwind",
  method = "bilinear"
)

Arguments

rose	wind_rose.
ll	longitude and latitude of site locations, as a two-column matrix.
threshold_km	a positive number representing the distance threshold, in kilometers. Site pairs closer together than this distance will get a separate local high-resolution connectivity model, while pairs farther apart will be modeled at the resolution of rose.
pad	a positive number indicating how far beyond a pair of sites the modeling domain should extend for local models. This is an expansion factor giving the padding as a fraction of the maximum latitudinal or longitudinal distance between the two sites. The default of 1 is reasonable in most cases; smaller values will increase computational speed but may fail to account for wind routes beyond the bounding box encompassing the site pair.
max_nodes	an integer representing how finely to interpolate wind grids for local site pairs. This represents the number of cells in the high-resolution interpolated grid for each site pair; larger values remove artifacts of the discrete coarse grid more effectively, but have increased computational cost.
direction	either "downwind" or "upwind", indicating whether outbound or inbound connectivity should be computed. In this context, changing this parameter is equivalent to transposing the resulting wind distance matrix.
method	disaggregation method; either "near" or "bilinear'; see disagg for details.

Value

A list of square matrices:

wind_dist

Wind cost-distances between site pairs, in hours if rose has a p = 1. Computed using costDistance.

wind_dist_coarse

Wind cost-distances using the coarse input wind grid (rose); this will differ from wind_dist only for site pairs closer than threshold_km. This is provided for reference, to judge how higher-resolution models impact results relative to the coarse grid.

point_dist

Distances between sites, in km.

cell_dist

Distances between the centroids of the grid cells used to model wind connectivity, in km. For site pairs where this distance deviates from point_dist by a substantial percentage, wind_dist estimates may contain nontrivial rounding noise resulting from the discrete grid.

cell_dist_coarse

Distances between the cell centroids in the coarse-resolution input wind dataset (rose), in km. This is provided for reference, to judge improvements relative to cell_dist.

matthewkling/windscape documentation built on Sept. 26, 2024, 4:22 p.m.