R_Calculating Thiessen weights for an area with irregular boundary

Hi R users,

I want to calculate Thiessen weights to compute areal rainfall from number
of point measurements. I am using R and thanks to some previous question in
the same topic, I got to know that I can usedeldir. But the problem is my
boundary polygon is not a rectangle; it's an irregular polygon (it's a
catchment boundary derived using ArcGIS). But in deldir the boundary can
only be a rectangle. Are there any other packages where I can calculate
Thiessen weights of an area covered by an irregular boundary?

Given below are my measurement points (meas_points) and coordinates of a
(simplified) boundary polygon(boundary)

meas_points

X      Y[1,] 415720 432795[2,] 415513 432834[3,] 415325
432740[4,] 415356 432847[5,] 415374 432858[6,] 415426 432774[7,]
415395 432811[8,] 415626 432762

boundary

x      y[1,] 415491 432947[2,] 415269 432919[3,] 415211
432776[4,] 415247 432657[5,] 415533 432657[6,] 415781 432677[7,]
415795 432836[8,] 415746 432937

Any help is really appreciated. Thanks.

cheers,

Mano