makeGrid: Make a Grid of Polygons

In PBSmapping: Mapping Fisheries Data and Spatial Analysis Tools

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".

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.

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, 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)
})

PBSmapping documentation built on Sept. 30, 2024, 9:21 a.m.