shp <- sf::read_sf("/vsicurl/https://github.com/wmgeolab/geoBoundaries/raw/main/releaseData/CGAZ/geoBoundariesCGAZ_ADM0.gpkg")
r <- controlledburn:::burn_polygon(shp, ext <- c(-180, 180, -90, 90), dm <- c(360, 180) * 4000)
## our index is triplets of start,end,line where the polygon edge was detected -
## this essentially an rle by scanline of start,end polygon coverage
index <- matrix(unlist(r, use.names = F), ncol = 4L, byrow = TRUE) + 1 ## plus one because 0-index internally
## plot just the start and ends of each scanline detected
xy0 <- vaster::xy_from_cell(dm, ext, vaster::cell_from_row_col(dm, t(index[,c(3, 3)]), t(index[,1:2])))
plot(xy0, pch = ".")
xy1 <- xy0[seq(1, nrow(xy0), by = 2), ]
xy2 <- xy0[seq(2, nrow(xy0), by = 2), ]
segments(xy1[,1], xy1[,2], xy2[,1], xy2[,2], col = palr::d_pal(rep(index[,4], each = 1)))
plot(xy0, pch = ".", xlim = c(140, 155), ylim = c(-20, 0))
segments(xy1[,1], xy1[,2], xy2[,1], xy2[,2], col = palr::d_pal(rep(index[,4], each = 1)))
plot(xy0, pch = ".", xlim = c(151, 151.2), ylim = c(-8.8, -8.3))
segments(xy1[,1], xy1[,2], xy2[,1], xy2[,2], col = palr::d_pal(rep(index[,4], each = 1)))
plot(shp, add = T)
cr <- do.call(rbind, apply(index, 1,\(.x) cbind(seq(.x[1], .x[2]), .x[3], .x[4])))
xy <- vaster::xy_from_cell(dm, ext, vaster::cell_from_row_col(dm, cr[,2], cr[,1]))
plot(xy, pch = 19, cex = .3, col = palr::d_pal(cr[,3]))
## how would we use cells?
## 1) area_from_row determine area (easy for longlat)
## 2) group up values (like area weighting)
## 3) values from other datasets (the one we rasterized from its definition)
## 4) efficient plotting of the scan lines
## 5) efficient conversion to polygon regions from raster
## 6) ability to crop
## 7) ability to farm out the job (but that's easy, just loop over chunks)
area_from_row <- function(dm, ext, row) {
SCALE <- 1852 * 60
lat <- vaster::y_from_row(dm, ext, row)
size <- vaster::x_res(dm, ext) * cos(lat * pi/180) * vaster::x_res(dm, ext) * SCALE
size
}
a <- area_from_row(dm, ext, cr[,2])
plot(xy, pch = 19, cex = .3, col = palr::d_pal(a))
