PBSmapping (version 2.72.1)

makeGrid: Make a Grid of Polygons

Description

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

Usage

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".

Value

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: \((x_{i}, y_{j}), (x_{i+1}, y_{j}), (x_{i+1}, y_{j+1}), (x_{i}, y_{j+1})\). The PolySet is a set of hexagonal grid cells when type='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 \(= i + (j - 1) \times (m - 1)\)

• byrow \(=\) FALSE and addSID \(=\) FALSE implies PID \(= j + (i - 1) \times (n - 1)\)

• 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.

See Also

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

Examples

# NOT RUN {
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)
})
# }