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Add Nearest Mapsheet Code and Center Coordinates

Source: R/assign_mapsheet.R
assign_mapsheet.Rd

This function takes an existing data frame with coordinate columns and appends:

  1. the nearest mapsheet code (format "E|WDDDN|SDDBB"), and

  2. the center longitude/latitude of that mapsheet.

Usage

assign_mapsheet(
  data,
  x_col = "x",
  y_col = "y",
  cell_size = 1,
  unit = c("deg", "min", "sec", "m")
)

Arguments

data

A data.frame containing at least the coordinate columns.

x_col

Character. Name of the longitude (x) column. Default "x".

y_col

Character. Name of the latitude (y) column. Default "y".

cell_size

Numeric. Cell size: e.g. 1 for 1° cells, 15 for 15′ cells.

unit

Character. Unit of cell_size; one of:

  • "deg" for decimal degrees (default)

  • "min" for arc-minutes

  • "sec" for arc-seconds

  • "m" for metres (projected coords).

Value

The input data with three new columns:

  • mapsheet: the 7-character sheet code

  • center_lon: centre longitude of that sheet

  • center_lat: centre latitude of that sheet

Details

It divides the world into regular grid cells (in degrees, minutes, seconds, or metres), finds which cell each point falls into, and then formats the sheet code based on the cell centre.

Examples

bird_obs = data.frame(
  site_id = 1:6,
  x = c(22.71862, 20.40034, 18.51368, 18.38477, 23.56160, 18.87285),
  y = c(-33.98912, -34.45408, -34.08271, -34.25946, -33.97620, -34.06225),
  species = c("Fulica cristata", "Numida meleagris coronatus",
              "Anas undulata", "Oenanthe familiaris",
              "Cyanomitra veroxii", "Gallinula chloropus"),
  value = rep(1, 6),
  year = c(2023, 2022, 2023, 2016, 2016, 2019),
  month = c(5, 12, 10, 8, 9, 2),
  day = c(12, 4, 3, 1, 4, 21)
)

# For 1° mapsheet cells:
bird_obs2 = assign_mapsheet(bird_obs, cell_size = 1, unit = "deg")
head(bird_obs2)
#>   site_id        x         y                    species value year month day
#> 1       1 22.71862 -33.98912            Fulica cristata     1 2023     5  12
#> 2       2 20.40034 -34.45408 Numida meleagris coronatus     1 2022    12   4
#> 3       3 18.51368 -34.08271              Anas undulata     1 2023    10   3
#> 4       4 18.38477 -34.25946        Oenanthe familiaris     1 2016     8   1
#> 5       5 23.56160 -33.97620         Cyanomitra veroxii     1 2016     9   4
#> 6       6 18.87285 -34.06225        Gallinula chloropus     1 2019     2  21
#>   center_lon center_lat  mapsheet
#> 1       22.5      -33.5 E022S34BB
#> 2       20.5      -34.5 E020S35BB
#> 3       18.5      -34.5 E018S35BB
#> 4       18.5      -34.5 E018S35BB
#> 5       23.5      -33.5 E023S34BB
#> 6       18.5      -34.5 E018S35BB