This function computes an appropriate observation window on which to perform prediction. Since the FFT grid
must have dimension 2^M by 2^N for some M and N, the window xyt$window, is extended to allow this to be fit in for a given cell width.
# S3 method for stppp
selectObsWindow(xyt, cellwidth, ...)an object of class stppp
size of the grid spacing in chosen units (equivalent to the cell width argument in lgcpPredict)
additional arguments
a resized stppp object together with grid sizes M and N ready for FFT, together with the FFT grid locations, can be useful for estimating lambda(s)
!!NOTE!! that this function also returns the grid ($xvals and $yvals) on which the FFT (and hence MALA) will be performed. It is useful to define spatialAtRiskobjects on this grid to prevent loss of information from the bilinear interpolation that takes place as part of the fitting algorithm.