  We report on the spatial response characterization of large LaCl$_{3}$(Ce)
monolithic crystals optically coupled to 8$\times$8 pixel silicon
photomultiplier (SiPM) sensors. A systematic study has been carried out for 511
keV $\gamma$-rays using three different crystal thicknesses of 10 mm, 20 mm and
30 mm, all of them with planar geometry and a base size of 50$\times$50 mm$^2$.
In this work we investigate and compare two different approaches for the
determination of the main $\gamma$-ray hit location. On one hand, methods based
on the fit of an analytical model for the scintillation light distribution
provide the best results in terms of linearity and field of view, with spatial
resolutions close to $\sim$1 mm FWHM. On the other hand, position
reconstruction techniques based on neural networks provide similar linearity
and field-of-view, becoming the attainable spatial resolution $\sim$3 mm FWHM.
For the third space coordinate $z$ or depth-of-interaction we have implemented
an inverse linear calibration approach based on the cross-section of the
measured scintillation-light distribution at a certain height. The detectors
characterized in this work are intended for the development of so-called Total
Energy Detectors with Compton imaging capability (i-TED), aimed at enhanced
sensitivity and selectivity measurements of neutron capture cross sections via
the time-of-flight (TOF) technique.
