Convert equal-area quarter-degree grid cell codes to latitude and longitude

This is a helper function that takes a vector of EQDGC (Equal-Area Quarter-Degree Grid Cell) codes and converts them to their central latitude and longitude coordinates. The function parses the base coordinates and the nested sub-grid codes to precisely locate the center of each grid cell.

Usage

convert_eqdgc_latlong(cellCode)

Arguments

cellCode

A character vector of EQDGC cell codes, which must follow the "direction-base_coord" format (e.g., "W10N34" or "E15S20"). The code can also contain additional letter characters for sub-grids (e.g., "W10N34A").

Value

A matrix with two columns, lat and long, representing the central coordinates of each input grid cell.

Details

The function works by first extracting the base longitude and latitude coordinates from the cell code, accounting for direction (East/West and North/South). It then iteratively processes any sub-grid codes (e.g., A, B, C, D) to refine the coordinates. The final coordinates are the center point of the most specific grid cell.

Examples

# A simple quarter-degree cell
convert_eqdgc_latlong("E10N10")
#>       lat long
#> [1,] 10.5 10.5

# A sub-grid cell
convert_eqdgc_latlong("W-10S34ABCD")
#>            lat      long
#> [1,] -34.21875 -10.65625

# Multiple cell codes
convert_eqdgc_latlong(c("E10N10", "W-10S34DDBA"))
#>            lat      long
#> [1,]  10.50000  10.50000
#> [2,] -34.78125 -10.09375