Context : While Gaia enables to probe in great detail the extended local neighbourhood , the thin disk structure at larger distances remains sparsely explored .

Aims : We aim here to build a non-parametric 3D model of the thin disc structures handling both the extinction and the stellar density simultaneously .

Methods : We developed a Bayesian deconvolution method in two dimensions : extinction and distance .
It uses a reference catalogue which completeness information defines the selection function .
It is designed so that any complementary information from other catalogues can be added .
It has also been designed to be robust to outliers , frequent in crowded fields , and differential extinction .
The prior information is designed to be minimal : only a reference H-R diagram .
We derived for this an empirical H-R diagram of the thin disk using Gaia DR2 data and synthetic isochrone-based H-R diagrams can also be used .

Results : We validated the method on simulations and real fields using 2MASS and UKIDSS data complemented by Gaia DR2 photometry and parallaxes .
We detail the results of two test fields : a 2MASS field centred around the NGC 4815 open cluster which shows an over-density of both extinction and stellar density at the cluster distance , and a UKIDSS field at l = 10 \degr where we recover the position of the Galactic bar .

Conclusions :