geodesic distance between two points, obtained via an API

Usage

distance_epa_api(
  lat1,
  lon1,
  lat2,
  lon2,
  pts = NULL,
  unit = "miles",
  crs = 4269
)

lat1, lon1: latitude and longitude of point 1
lat2, lon2: latitude and longitude of point 2
pts: Alternative way to specify the two points, as a data.frame of two rows and columns named "lat" and "lon"
unit: can be "miles", the default, or else "meters" to get distance in meters. unit is called distanceUnit in the API: For planar distance, if distanceUnit is not specified, the distance is in the units of the given spatial reference. If distanceUnit is specified, the unit must be compatible with the given spatial reference. That is, if sr is a PCS, distanceUnit must be linear. If sr is a GCS, distanceUnit must be angular. For geodesic distance, If distanceUnit is not specified, the distance is measured in meters. If distanceUnit is specified, the unit must be linear.
crs: default spatial reference is 4269 aka Geodetic CRS NAD83. crs, called sr in the API, specifies the well-known ID (WKID) or a spatial reference JSON object for input geometries. The spatial reference can be either a projected coordinate system (PCS) or a geographic coordinate system (GCS). For a list of valid WKID values, see Using spatial references

a single number, the distance

pts <- testpoints_10[c(3,10),]
distances.all(pts[1,],pts[2,])
d <- distance_epa_api(pts = pts)
print(d)
mapfast(pts, radius = d/2)