  Interferometers play an increasingly important role for spatially resolved
observations. If employed at full potential, interferometry can probe an
enormous dynamic range in spatial scale. Interpretation of the observed
visibilities requires the numerical compu- tation of Fourier integrals over the
synthetic model images. To get the correct values of these integrals, the model
images must have the right size and resolution. Insufficient care in these
choices can lead to wrong results. We present a new general-purpose scheme for
the computation of visibilities of radiative transfer images. Our method
requires a model image that is a list of intensities at arbitrarily placed
positions on the image-plane. It creates a triangulated grid from these
vertices, and assumes that the intensity inside each triangle of the grid is a
linear function. The Fourier integral over each triangle is then evaluated with
an analytic expression and the complex visibility of the entire image is then
the sum of all triangles. The result is a robust Fourier trans- form that does
not suffer from aliasing effects due to grid regularities. The method
automatically ensures that all structure contained in the model gets reflected
in the Fourier transform.
