This is an example of architectural true-othoimage with re-lighting capabilities.

The whole process is achieved departing only from photographs. Several snapshots of the door where taken using a calibrated digital camera with some particular settings (fixed focus and focal lenght, manual exposure, low ISO, etc...).

A basic three-dimensional dense geometry reconstruction is performed by means of dense stereo and SfM methods. This provides depth information to an scale in the millimeter range.

A few more photographs where taken within a few hours interval with varying environmental lighting conditions, including sunlight and overcast. Using this information an illumination model is built and some properties of the BSDF (Bidirectional Scattering Distribution Function) of the surfaces are deduced from the different lighting settings. This allows to produce an specially built bi-directional shader function to reproduce any new lighting condition including arbitrary new angles for sun incidence.

Additionally fine details in the surface relief are revealed by a normal map produced by a simplified photometric stereo reconstruction method. Direct and indirect shadows, as well as Indirect light scattering are also modeled providing a high degree of realism to the final render.

This is quite practical to provide unified and convenient illumination conditions to complex ortho-image documents and to enhance depth perception and to provide the volumetric information in the representation that is often missing from planar orthoimages.

Antonio Martos, Advision 2013

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