makeGrid function

Make a Grid of Polygons

Make a grid of polygons, using PIDs and SIDs according to the input arguments.

makeGrid(x, y, byrow=TRUE, addSID=TRUE, 
   projection=NULL, zone = NULL, type="rectangle")

Arguments

• x: numeric -- vector of X-coordinates (of length $m$).

• y: numeric -- vector of Y-coordinates (of length $n$).

• byrow: logical -- if TRUE and type='rectangle', increment PID along X (column-wise);

  -- if TRUE and type='hexagon', create flat-topped hexagons contiguous by column and increment PID by column;

  -- if FALSE and type='hexagon', create pointy-topped hexagons contiguous by row and increment PID by row.

• addSID: logical -- if TRUE, include an SID field in the resulting PolySet , incremented by the alternative dimension used by PID.

• projection: character -- optional projection attribute to add to the PolySet.

• zone: numeric -- optional zone attribute to add to the PolySet.

• type: character -- type of regular tesselation; choices: "rectangle" or "hexagon".

Details

This function makes a grid of polygons, labeling them according to byrow and addSID.

For rectangular tesselations (grid cells), the variables $i$ and $j$

indicate column and row numbers, respectively, where the lower-left cell of the grid is (1, 1):

• byrow $=$ TRUE and addSID $=$

  FALSE implies PID $= i + (j - 1) * (m - 1)$

• byrow $=$ FALSE and addSID $=$

  FALSE implies PID $= j + (i - 1) * (n - 1)$

• byrow $=$ TRUE and addSID $=$

  TRUE implies PID $= i$, SID $= j$

• byrow $=$ FALSE and addSID $=$

  TRUE implies PID $= j$, SID $= i$

For hexagonal tesselations (grid cells), $i$ indicates columns for flat-topped hexagons and rows for pointy-topped hexagons. The reverse is true for $j$. Stemming from their six-sided nature, hexagons will adjoin along a long-edge by row when their orientation is such that one vertex is higher than all the others. Hexagons will adjoin along a long-edge by column when their orientation shows two uppermost vertices.

Returns

PolySet with columns PID, SID

(if addSID=TRUE), POS, X, and Y.

The PolySet is a set of rectangular grid cells when type='rectangle', with vertices:

c("$(x_i, y_j), (x_(i+1), y_j), (x_(i+1), y_(j+1)),\n$", "$(x_i, y_(j+1))$").

The PolySet is a set of hexagonal grid cells when type='hexagon'.

Author(s)

Nicholas M. Boers, Staff Software Engineer

Jobber, Edmonton AB

Rowan Haigh, Program Head -- Offshore Rockfish

Pacific Biological Station (PBS), Fisheries & Oceans Canada (DFO), Nanaimo BC

locus opus: Institute of Ocean Sciences (IOS), Sidney BC

Last modified Rd: 2019-01-04

See Also

addPolys, clipPolys, combineEvents, findCells, findPolys, thickenPolys.

Examples

local(envir=.PBSmapEnv,expr={
  oldpar = par(no.readonly=TRUE)
  ##--- make a 10 x 10 grid
  polyGrid <- makeGrid(x=0:10, y=0:10)
  ##--- plot the grid
  plotPolys(polyGrid, density=0, projection=1)
  par(oldpar)
})