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 with in resistance units. See Details.
points	A two-column matrix, data.frame, (including tibble types) with longitude (x) in the first column and latitude (y) in the second, or a SpatVector, 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.

Pre-prepared walking or motorised friction surfaces can be obtained with?get_friction_surface. User can also provide their own friction surface. This surface but must be in resistance units (1/conductance), e.g. minutes/meter. See Van Etten 2017.

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. https://doi:10.1038/nature25181

van Etten, J. (2017). R package gdistance: Distances and routes on geographical grids. Journal of Statistical Software https://doi.org/10.18637/jss.v076.i13

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)

---

Convert extent to matrix

Description

This function allows get_friction_surface() to accept the argument extent as a vector, 2x2 matrix, SpatVector, or SpatRaster and extracts and converts into the annoyingly specific format necessary to download the friction surface. See details in ?get_friction_surface

Usage

ext_matrix(extent)

Arguments

extent

vector of length 4, 2x2 matrix, SpatExtent, SpatVector, or SpatRaster

Value

2x2 matrix with column names "x" and "y" and row names "min" and "max"

Examples

# vector/double
x <- c(111, 112, 0, 1)
ext_matrix(x)

# SpatExtent
y <-  terra::ext(x)
ext_matrix(y)

# SpatRaster
r <- terra::rast(extent = y)
ext_matrix(r)

# SpatVector
v <- terra::vect(y)
ext_matrix(v)

---

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 one of: a numeric vector specifying c(xmin, xmax, ymin, ymax), a terra SpatExtent, SpatVector, or SpatRaster from which the extent will be taken, or 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/.

Here —

• surface = "motor2020" will download "Explorer__2020_motorized_friction_surface", and

• surface = "walk2020" will download "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 formatted and then passed through to malariaAtlas::getRaster() as a 2x2 matrix. It is converted into a matrix using ext_matrix. The matrix format used 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"))). NULL extent downloads (large) global layer.

Troubleshooting: if you get a warning ⁠Failed to connect to MAP geoserver⁠, this is an issue with fetching the friction surface using malariaAtlas::getRaster, and not an issue with traveltime itself. The server may be down or there may be an issue with that package.

Value

SpatRaster

Examples

# for more examples of passing exten types see ?ext_matrix

ext <- c(111, 112, 0, 1)

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

---

Singapore MRT and LRT data

Description

Locations of all MRT and LRT station exits in Singapore.

Usage

stations

Format

stations A data frame with 563 rows and 2 columns:

x

longitude

y

latitude

Source

Land Transport Authority. (2019). LTA MRT Station Exit (GEOJSON) (2024) Dataset. data.gov.sg. Retrieved December 10, 2024 from https://data.gov.sg/datasets/d_b39d3a0871985372d7e1637193335da5/view

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