create neighbourhood (nb) object from grid geometry

`gridIndex2nb(obj, maxdist = sqrt(2), fullMat = TRUE, ...)`

Object of class nb, which is a list.

The nb object follows the convention of nb objects in package spdep; it is a list with each list element corresponding to a grid cell or pixel; the list element contains the indices of neighbours defined as cells less than maxdist away, measured in cell unit (N/S/E/W neighbour has distance 1).

- obj
object of class SpatialGrid or SpatialPixels

- maxdist
maximum distance to be considered (inclusive), expressed in number of grid cell (sqrt(2) results in queen neighbours)

- fullMat
use dist to compute distances from grid (row/col) indices; FALSE avoids forming the full distance matrix, at a large performance cost

- ...
arguments passed on to dist

Edzer Pebesma, edzer.pebesma@uni-muenster.de

plot.nb in package spdep