  This study proposes an analytical framework for deriving the surface
brightness profile and geometry of a geometrically-thin axisymmetric disc from
interferometric observation of continuum emission. Such precise modelling
facilitates the exploration of faint non-axisymmetric structures, such as
spirals and circumplanetary discs. As a demonstration, we simulate
interferometric observations of geometrically-thin axisymmetric discs. The
proposed method can reasonably recover the injected axisymmetric structures,
whereas Gaussian fitting of the same data yielded larger errors in disc
orientation estimation. To further test the applicability of the method, it was
applied to the mock data for $m=1,2$ spirals and a point source, which are
embedded in a bright axisymmetric structure. The injected non-axisymmetric
structures were reasonably recovered except for the innermost parts, and the
disc geometric parameter estimations were better than Gasussian fitting. The
method was then applied to the real data of Elias 20 and AS 209, and it
adequately subtracted the axisymmetric component, notably in Elias 20, where
substantial residuals remained without our method. We also applied our method
to continuum data of PDS 70 to demonstrate the effectiveness of the method. We
successfully recovered emission from PDS 70 c consistently with previous
studies, and also tentatively discovered new substructures. The current
formulation can be applied to any data for disc continuum emission, and aids in
the search of spirals and circumplanetary discs, whose detection is still
limited.
