Package 'traveltime'

Calculate travel time

Description

Calculate the travel time from a set of points over a friction surface.

Usage

calculate_travel_time(
  friction_surface,
  points,
  filename = NULL,
  overwrite = FALSE
)

Arguments

friction_surface	A SpatRaster friction surface layer. See ?get_friction_surface
points	A two-column data.frame or tibble with longitude (x) in the first column and latitude (y) in the second in the same coordinate reference system as friction_surface
filename	character. Output file name with extension suitable for terra::writeRaster
overwrite	logical. If TRUE filename is overwritten.

Details

Implements methods from Weiss et al. 2018, 2020 to calculate travel time from given locations over a friction surface.

Over large areas this function can require significant RAM and will be slow.

Citations: D. J. Weiss, A. Nelson, C. A. Vargas-Ruiz, K. Gligoric, S., Bavadekar, E. Gabrilovich, A. Bertozzi-Villa, J. Rozier, H. S. Gibson, T., Shekel, C. Kamath, A. Lieber, K. Schulman, Y. Shao, V. Qarkaxhija, A. K. Nandi, S. H. Keddie, S. Rumisha, P. Amratia, R. Arambepola, E. G. Chestnutt, J. J. Millar, T. L. Symons, E. Cameron, K. E. Battle, S. Bhatt, and P. W. Gething. Global maps of travel time to healthcare facilities. (2020) Nature Medicine. https://doi.org/10.1038/s41591-020-1059-1

D. J. Weiss, A. Nelson, H.S. Gibson, W. Temperley, S. Peedell, A. Lieber, M. Hancher, E. Poyart, S. Belchior, N. Fullman, B. Mappin, U. Dalrymple, J. Rozier, T.C.D. Lucas, R.E. Howes, L.S. Tusting, S.Y. Kang, E. Cameron, D. Bisanzio, K.E. Battle, S. Bhatt, and P.W. Gething. A global map of travel time to cities to assess inequalities in accessibility in 2015. (2018). Nature. doi:10.1038/nature25181.

Value

SpatRaster

Examples

ext <- matrix(
  data = c("111", "0", "112", 1),
  nrow = 2,
  ncol = 2,
  dimnames = list(
    c("x", "y"),
    c("min", "max")
   )
 )

 friction_surface <- get_friction_surface(
   surface = "motor2020",
   extent = ext
 )

 from_here <- data.frame(
   x = c(111.2, 111.9),
   y = c(0.2, 0.35)
 )

 calculate_travel_time(
  friction_surface = friction_surface,
  points = from_here
 )

---

Extent from SpatRaster or SpatVector

Description

Formats spatial extent for use in get_friction_surface.

Usage

ext_from_terra(r)

Arguments

r	terra::SpatRaster or terra::SpatVector

Value

2x2 matrix

Examples

library(terra)
r <- terra::rast(
    extent = terra::ext(c(111, 112, 0, 1))
  )

ext_from_terra(r)

---

Extent vector to matrix

Description

Extent vector to matrix

Usage

ext_vect_to_matrix(x)

Arguments

x	numeric length 4, consisting of c(xmin, xmax, ymin, ymax) dimensions of extent

Value

2x2 matrix

Examples

ext_vect_to_matrix(c(111,112,0, 1))

---

Get friction surface

Description

Wrapper function to download friction surfaces via malariaAtlas::getRaster

Usage

get_friction_surface(
  surface = c("motor2020", "walk2020"),
  filename = NULL,
  overwrite = FALSE,
  extent = NULL
)

Arguments

surface	"motor2020" or ⁠"walk2020⁠.
filename	character. File name for output layer.
overwrite	Overwrite filename if exists
extent	Spatial extent as either numeric vector specifying c(xmin, xmax, ymin, ymax), SpatExtent, SpatVector or SpatRaster (from which the extent will be taken), or 2x2 matrix (see details).

Details

Convenience wrapper to malariaAtlas::getRaster to access motorised and walking travel friction layers per Weiss et al. 2020, that adds safety to check existing files before download. Surfaces can be downloaded directly from: https://malariaatlas.org/project-resources/accessibility-to-healthcare/

surface = "motor2020" downloads "Explorer__2020_motorized_friction_surface".

surface = "walk2020" downloads "Explorer__2020_walking_only_friction_surface".

D. J. Weiss, A. Nelson, C. A. Vargas-Ruiz, K. Gligoric, S., Bavadekar, E. Gabrilovich, A. Bertozzi-Villa, J. Rozier, H. S. Gibson, T., Shekel, C. Kamath, A. Lieber, K. Schulman, Y. Shao, V. Qarkaxhija, A. K. Nandi, S. H. Keddie, S. Rumisha, P. Amratia, R. Arambepola, E. G. Chestnutt, J. J. Millar, T. L. Symons, E. Cameron, K. E. Battle, S. Bhatt, and P. W. Gething. Global maps of travel time to healthcare facilities. (2020) Nature Medicine. https://doi.org/10.1038/s41591-020-1059-1

extent is passed through is to pass to malariaAtlas::getRaster as a 2x2 matrix. If passed in as a numeric vector, SpatExtent, SpatVector, or SpatRaster, it is converted into a matrix using ext_vect_to_matrix and ext_from_terra. matrix format is as returned by sf::st_bbox() - the first column has the minimum, the second the maximum values; rows 1 & 2 represent the x & y dimensions respectively (matrix(c("xmin", "ymin","xmax", "ymax"), nrow = 2, ncol = 2, dimnames = list(c("x", "y"), c("min", "max")))) (use either shp OR extent; if neither is specified global raster is returned). NULL extent downloads (large) global layer.

Additional details...

Value

SpatRaster

Examples

ext <- matrix(
  data = c(111, 0, 112, 1),
  nrow = 2,
  ncol = 2,
  dimnames = list(
    c("x", "y"),
    c("min", "max")
   )
 )

 get_friction_surface(
   surface = "motor2020",
   extent = ext
 )

---