footprint

The goal of footprint bin point data at very high resolution, storing a sparse grid. These tools use spatstat.geom and terra packages.

It just exists as the code used in abstraction from the work done in 2015. I’d be happy to collab to extend this to new work.

Installation

You can install the development version of footprint from GitHub with:

# install.packages("pak")
pak::pak("hypertidy/footprint")

We create a massive raster, a fair number of pretty short line segments, then bin those lines and record cell hits of the massive raster (we convert from child raster touched by the line segment). The output is ‘cell’, a pretty massive data frame of cell,prob(ability).

Then, we bin the count of lowest resolution pixels touched by a line into a much lower resolution raster and plot it with the lines.

It still takes a while, a few minutes parallelized and the summary stage takes longer than the rasterizing now, it and perhaps a few other speedups are available.

library(footprint)  
library(terra)
#> terra 1.7.3
library(spatstat.geom)
#> Loading required package: spatstat.data
#> spatstat.geom 3.0-3
#> 
#> Attaching package: 'spatstat.geom'
#> The following objects are masked from 'package:terra':
#> 
#>     area, delaunay, rescale, rotate, shift, where.max, where.min
library(dplyr)
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:terra':
#> 
#>     intersect, union
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union
llproj <- "+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0"
proj <- "+proj=laea +lat_0=-90 +datum=WGS84 +units=m +no_defs +ellps=WGS84 +towgs84=0,0,0"

## very round-a-bout, but works
ex <- ext(project(rast(ext(100, 120, -60, -50), nrow = 100, ncol = 100, crs = llproj), proj))

## parent grid (sparse massive grid with 15m pixels)
g <- buildparent(ex, 15)

print(g)  ## don't ever populate the data of this object :)
#> class       : SpatRaster 
#> dimensions  : 107045, 95862, 1  (nrow, ncol, nlyr)
#> resolution  : 15, 15  (x, y)
#> extent      : 2866380, 4304310, -2180415, -574740  (xmin, xmax, ymin, ymax)
#> coord. ref. :

n <- 1e4
pts0 <- cbind(runif(n, xmin(g) + 3000 , xmax(g) - 3000), runif(n,ymin(g) + 3000, ymax(g) - 3000))
pts1 <- cbind(rnorm(n, pts0[,1], 500), rnorm(n, pts0[,2], 1500))

psegs <- function(x1, x2, add = FALSE) {
  if (!add) plot(rbind(x1, x2), type = "n")
  segments(x1[,1], x1[,2], x2[,1], x2[,2])
}
psegs(pts0, pts1)

diam <- rep(30, nrow(pts0))  ## diameter for density (can be per row )

Kcell <- vector("list", nrow(pts1))
kde <- FALSE

## this could be made a lot faster now 2023-08-07
## --parallelize the loop
## -- (possibly rasterize with terra, can't do kde)
## -- probably can rewrite a fair bit anyway
# for (i in seq(nrow(pts1))) {
#   linp <- bpsp(pts0[i,], pts1[i,], g, diam[i]/2)
#   if (kde) {
#    pix <- density(linp, sigma = diam[i])
#   } else {
#    pix <- pixellate(linp)
#   }
#   rd <- rast(pix)
#   rd[rd < quantile(values(rd)[,1], 0.75)] <- NA_real_
#   
#   vals <- values(rd)
#   Kcell[[i]] <- tibble::tibble(cell = cellFromXY(g, xyFromCell(rd, seq_len(ncell(rd)))[!is.na(vals), ]), 
#         prob = na.omit(vals))  
# if (i %% 50 == 0) print(i)
# }

## this fuction is the old loop above in parallel, which was much harder to do when it was written
## this document is run from the shell via Rscript -e 'rmarkdown::render("README.Rmd")' &
## because, note limitations on future::multicore when run in RStudio
fun_pti <- function(i) {
   linp <- bpsp(pts0[i,], pts1[i,], g, diam[i]/2)
  if (kde) {
   pix <- density(linp, sigma = diam[i])
  } else {
   pix <- pixellate(linp)
  }
  rd <- rast(pix)
  ## values() clashes with future::values 
  rd[rd < quantile(terra::values(rd)[,1], 0.75)] <- NA_real_
  
  vals <- terra::values(rd)
  tibble::tibble(cell = cellFromXY(g, xyFromCell(rd, seq_len(ncell(rd)))[!is.na(vals), ]), 
        prob = na.omit(vals)) 
}

library(furrr)
#> Loading required package: future
#> 
#> Attaching package: 'future'
#> The following object is masked from 'package:terra':
#> 
#>     values
plan(multicore)
Kcell <- future_map(seq_len(nrow(pts1)), fun_pti)
plan(sequential)

## summarize with dplyr
cell <- do.call(bind_rows, Kcell)

ss <- cell %>% group_by(cell) %>% summarize(prob = sum(prob))

rsum <- setValues(rast(ext(g), res = 50000, crs = crs(g)), 0)
ss$foreign <- cellFromXY(rsum, xyFromCell(g, ss$cell))
xsum <- ss %>% group_by(foreign) %>% summarize(prob = sum(prob)) %>% filter(!is.na(foreign))
rsum[xsum$foreign] <- xsum$prob

plot(rsum)
psegs(pts0, pts1, add = TRUE)
ex2 <- ext(3064556.06339375, 3203002.1878131, -925364.448947992, -816064.877037982)
plot(ex2, add = TRUE)

## zoom in
plot(crop(rsum, ex2))
psegs(pts0, pts1, add = TRUE)

Code of Conduct

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