README.md

In kbvernon/hiker: Model Hiking Paths Over Costly Terrains

hiker

The hiker package aids in the modeling of specifically human movement across a landscape. Much of its code was inspired by Jacob van Etten’s (2017) gdistance package, though it works with more modern spatial tools, specifically sf and terra.

Installation

The hiker package is not currently on CRAN, though that will hopefully change soon enough. In the meantime, you can download and install the development version using:

install.packages("remotes")
remotes::install_github("kbvernon/hiker")

Example

Consider the Red Butte Canyon Research Natural Area in the Wasatch Foothills above the University of Utah. If I wanted to hike up this canyon in the shortest time possible, what route should I take?

library(hiker)
library(sf)
library(terra)
library(viridis)

fn <- system.file("extdata/red_butte_dem.tif", package = "hiker")
red_butte_dem <- rast(fn)

from <- st_sf(
  geometry = st_sfc(st_point(c(432000, 4513100))),
  crs = 26912
)

to <- st_sf(
  geometry = st_sfc(st_point(c(436750, 4518500))),
  crs = 26912
)

To figure out the “shortest” path from start to end, we need to have some sense of the time it would take to move through any particular location in the canyon. This cost surface is the terrain we are hiking in R.

(terrain <- hf_terrain(red_butte_dem))
#> class       : terrain 
#> dimensions  : 268, 260, 69680 (nrow, ncol, ncell)
#> resolution  : 26.48, 26.48 (x, y)
#> extent      : 430567.2 437451.2 4512415 4519511 (xmin, xmax, ymin, ymax)
#> coord.ref   : EPSG 26912 
#> min cost    : 9.98 
#> max cost    : 75.86

# to adjust legend (plg) and axis (pax) text size
pax <- list(cex.axis = 0.65)
plg <- list(cex = 0.65)

plot(terrain, 
     col = viridis(50), 
     pax = pax, 
     plg = plg)

title(main = "Travel Cost (sec)", adj = 0, line = 0.3)

The next step is to simply pass the start and end point, along with the cost surface, to one of our three path functions. For instance, hf_hike() computes shortest paths and returns them as sf objects.

short_path <- hf_hike(terrain, from, to)

short_path
#> Simple feature collection with 1 feature and 2 fields
#> Geometry type: LINESTRING
#> Dimension:     XY
#> Bounding box:  xmin: 432010.2 ymin: 4513090 xmax: 436749.6 ymax: 4518492
#> Projected CRS: NAD83 / UTM zone 12N
#>   from to                       geometry
#> 1    1  1 LINESTRING (432010.2 451309...

Now we can visualize this short_path.

plot(red_butte_dem, 
     col = viridis(50),
     pax = pax, 
     plg = plg)

title(main = "Path over Elevation (m)", adj = 0, line = 0.3)

plot(st_geometry(short_path),
     col = "white",
     lwd = 1.5,
     add = TRUE)

plot(st_geometry(from), 
     pch = 21, 
     cex = 1.3, 
     bg = "red2", 
     col = "white", 
     add = TRUE)

plot(st_geometry(to), 
     pch = 21, 
     cex = 1.3, 
     bg = "dodgerblue3", 
     col = "white", 
     add = TRUE)

Alternative packages

I am aware of three packages that offer similar functionality:

• leastcostpath,
• movecost, and
• marmap

The hiker package differs from these packages in the following ways:

1. hiker is simple. The package is somewhat singular in purpose and many arguably reasonable assumptions come baked in. This makes for much simpler code and a more user-friendly API.
2. hiker is tidy (or tries to be). As much as possible, code is written to comport with the tidyverse style guide, mostly thanks to usethis::use_tidy_style(), and development largely follows the guidelines described in Wickham and Bryan’s R Packages.
3. hiker uses sf rather than its predecessor sp.
4. hiker uses terra instead of its predecessor raster.

References

Campbell, Michael J., Philip E. Dennison, Bret W. Butler, and Wesley G. Page (2019). “Using crowdsourced fitness tracker data to model the relationship between slope and travel rates. Applied Geography 106, 93-107. https://doi.org/10.1016/j.apgeog.2019.03.008

Tobler, Waldo R. (1993). “Three Presentations on Geographical Analysis and Modeling: Non-Isotropic Geographic Modeling, Speculations on the Geometry of Geography, and Global Spatial Analysis.” National Center for Geographic Information and Analysis, Technical Report 93-1.

van Etten, Jacob (2017). “R package gdistance: Distances and routes on geographical grids.” Journal of Statistical Software, 76(1), 1–21. https://doi.org/10.18637/jss.v076.i13

Code of Conduct

Please note that the hiker project is released with a Contributor Code of Conduct. By contributing to this project, you agree to abide by its terms.

kbvernon/hiker documentation built on Dec. 9, 2022, 11:16 p.m.