makeGrid: Make a Grid of Polygons

Description Usage Arguments Details Value Author(s) See Also Examples

Description

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

Usage

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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):

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.

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'.

Author(s)

Nicholas M. Boers, Associate Professor – Computer Science
MacEwan University, 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

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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)
})

PBSmapping documentation built on Jan. 15, 2021, 3:41 p.m.