[R] Boundaries and deldir

[p_connolly]

Just what is meant by dummy points as referred to by the help for the
deldir() function?  I understood they indicated the boundary beyond
which triangulation would cease.

I thought I would need the x/y elements (as described in the help file
at the end of the description of the use of the dpl argument) to
describe ad hoc dummy points as way to define a polygon or two as a
boundary.  However, it gives this error:

Error in xd[-drop] : only 0's may be mixed with negative subscripts

Something internal is doing the negative subscripting.
I tried ndx/ndy instead of x/y but it evidently refers only to a
rectangle so not what I need.

Am I barking up the wrong tree altogether?  Is the boundary defined
somewhere else entirely?  I need to get that clear before I am able to 
provide
useful example code.

TIA
Patrick