get_barrier_intersect: Get distance between points taking into account barriers
In mrc-ide/PlasmoMAPI: Mapping Plasmodium Spatial Connectivity from Genetic Data

Given a set of lat/lon coordinates and a list of barriers in the form of polygons, returns the "distance" between points where distance is equal to the great-circle distance with a penalty applied if the line intersects a barrier. The exact way in which barriers modify distances can be varied (see barrier_method argument).

get_barrier_intersect(
  node_long,
  node_lat,
  barrier_list = list(),
  barrier_penalty = numeric(),
  barrier_method = 1,
  max_barrier_range = Inf,
  eccentricity = 0.9,
  n_ell = 20
)

`node_long`	longitudes of nodes.
`node_lat`	latitudes of nodes.
`barrier_list`	list of polygons representing barriers. Each element of the list must be a dataframe with columns `long` and `lat` specifying the coordinates of points that make up the polygon. Polygons must be complete rings, meaning the final row of the dataframe must equal the first row.
`barrier_penalty`	penalty values of each barrier. If a single value is provided then this value will be used for all barriers.
`barrier_method`	the method by which penalties are applied: compare pairwise lines to barriers. If the line intersects then add a fixed `barrier_penalty` to the spatial distance. compare pairwise lines to barriers. Calculate the intersection of the two, multiply this by the `barrier_penalty` and add to the spatial distance. For example, a `barrier_penalty` of 1 would mean there is double the "friction" when moving through a barrier. compare pairwise ellipses to barriers. Calculate the intersection area of the two, multiply this by the `barrier_penalty` and add to the spatial distance.
`max_barrier_range`	edges that are longer than this distance are unaffected by any barriers. Makes it possible to model barriers that only apply locally.
`eccentricity`	eccentricity of ellipses (only used under `barrier_method = 3`).
`n_ell`	number of points that make up an ellipse (only used under `barrier_method = 3`).