Gate the grid crosswalk

What must hold for grid_crosswalk to be the map between the two grids: every previous cell appears, every current cell appears, no pair repeats, every key is a cell of its grid, and no previous cell's shares sum to more than one (they would only if two current cells overlapped, and the current grid is a partition).

Usage

check_grid_crosswalk(
  con,
  grid_prev = calcofi4r::cc_grid_v1,
  tbl = "grid_crosswalk",
  grid_tbl = "grid",
  min_cover = 0.95,
  tol = 1e-06,
  halt = TRUE
)

Arguments

con

a DuckDB connection holding tbl and grid_tbl

grid_prev

the previous grid (default calcofi4r::cc_grid_v1); only its keys are read

tbl, grid_tbl

the crosswalk and the current grid tables

min_cover

the smallest summed share a cell may have (default 0.95; measured on the rebuilt grid: 0.978 for a previous cell, 0.982 for a current one)

tol

tolerance on a sum differing from one (default 1e-6)

halt

stop on a failure (default TRUE); FALSE returns the report regardless

Value

a data frame, one row per cell of either grid: side ("prev" or "grid"), grid_key, n (cells of the other grid it overlaps), frac (summed share), main_key (the other grid's cell holding its largest share), main_frac and status ("ok", "partial", "overlapped", or a failure: "no overlap", "under min_cover", "over one")

Details

Three things are reported rather than failed, because they are facts about the two grids and not errors in the map. A cell whose shares sum to less than one, down to min_cover, is "partial": the remainder is area the other grid does not cover (the previous cells were clipped by a coarser coastline, so part of one can be land now). Below min_cover it fails, since a cell most of which has no counterpart is a hole. A current cell whose shares sum to more than one is "overlapped": previous cells overlap each other there (the previous grid was assembled in +proj=calcofi and glued by hand along line 93.3, and is not an exact partition in longitude/latitude; seven current cells either side of that boundary are covered twice over at most 1e-4 of their area).