Polarised radio sources are conventionally analysed by using rotation-measure synthesis to produce the Faraday spectrum, showing the intensity of the flux that has propagated through different depths of magnetised plasma. An alternative approach is to use a model of the source to determine the expected radio emission and compare this to the measured data, using a technique such as nested sampling to explore the parameter space and find the best-fitting model. At the expense of additional processing power, this makes it possible to achieve a more precise reconstruction of the source, and a more rigorous distinction between different models for its structure. I will describe the implementation and some results of this approach.