The fraction of the width of the point pattern by which the box will
surround the point pattern to the left and right.
yfrac
The fraction of the height of the point pattern by which the box will
surround the point pattern to the top and bottom.
Value
A points data set of four points giving the coordinates of the surrounding box
References
Rowlingson, B. and Diggle, P. 1993 Splancs: spatial point pattern analysis
code in S-Plus. Computers and Geosciences, 19, 627-655;
the original sources can be accessed at:
http://www.maths.lancs.ac.uk/~rowlings/Splancs/. See also Bivand, R. and
Gebhardt, A. 2000 Implementing functions for spatial statistical analysis
using the R language. Journal of Geographical Systems, 2, 307-317.