  The application of orthonormal basis functions such as Prolate Spheroidal
Wave Functions (PSWF) for accurate source modeling in radio astronomy has been
comprehensively studied. They are of great importance for high fidelity, high
dynamic range imaging with new radio telescopes as well as conventional ones.
But the construction of PSWF is computationally expensive compared to other
closed form basis functions. In this paper, we suggest a solution to reduce its
computational cost by more efficient construction of the matrix kernel which
relates the image domain to visibility (or Fourier) domain. Radio astronomical
images are mostly represented using a regular grid of rectangular pixels. This
is required for efficient storage and display purposes and moreover, comes
naturally as a by product of the Fast Fourier Transform (FFT) in imaging. We
propose the use of Delaunay triangulation as opposed to regular gridding of an
image for a finer selection of the region of interest (signal support) during
the PSWF kernel construction. We show that the computational efficiency
improves without loss of information. Once the PSWF basis is constructed using
the irregular grid, we revert back to the regular grid by interpolation and
thereafter, conventional imaging techniques can be applied.
