ISEA Aperture 3 Hexagon (ISEA3H) DGG

Description:

These data were taken from here and contain ISEA discrete global grids (DGGs) generated using the DGGRID software. The available grids below correspond to the Aperture 3 Hexagons. Grids for other ISEA DGG topologies are available from the original website.

Format:

The grids are in ARC/INFO generate format, which is a simple text file format. All vertices are given in longitude and latitude in decimal degrees. Each file contains the cell boundaries for the entire globe at the specified resolution. Since cell boundaries are only true regular polygons in the ISEA projection space 3 additional points were added to each edge to better preserve the true boundary shape after projection into longitude/latitude coordinates.

Usage:

To read the data into R use the following code

library(dplyr)
library(ggplot2)
library(foreach)
library(zoo)

isea3h <- NULL
isea3h <- foreach(j = 0:8,.combine = "rbind") %do% {
    print(paste0("Processing resolution ",j))

    X <- read.table(paste0("isea3h",j,".gen"),
                             sep=" ",
                             fill=T,header=F,
                             col.names = c("id","lon","lat")) 
    X <- filter(X,!(id == "END"))
    X <- mutate(X,res = j,
           id = as.numeric(as.character(id)),
           centroid = as.numeric(!is.na(id)))
    X <- transform(X,id = na.locf(id))
    X
}
save(isea3h,file="./isea3h.rda")
ggplot(subset(isea3h,res==5)) +
          geom_point(aes(lon,lat,colour=centroid)) + 
          coord_map("ortho")

References:

Sahr, K. (2008) Location coding on icosahedral aperture 3 hexagon discrete global grids. Computers, Environment and Urban Systems, 32(3):174-187.