  We suggest a two-dimensional wavelet devised to deduce the large-scale
structure of a physical field (e.g., the Galactic magnetic field) from its
integrals along straight paths from irregularly spaced data points to a fixed
interior point (the observer). The method can be applied to the analysis of
pulsar rotation and dispersion measures in terms of the large-scale Galactic
magnetic field and electron density. The method does not use any 'a priori'
assumptions about the physical field and can be considered as an algorithm of
wavelet differentiation. We argue that a certain combination of the wavelet
transformation with model fitting would be most efficient in the interpretation
of the available pulsar RM data.
