Validation of a photogrammetric approach for the objective study of ancient bowed instruments

TL;DR

This paper presents a validated photogrammetric method for objectively analyzing ancient bowed instruments, enabling differentiation between reduced and unreduced violins through geometric analysis of 3D meshes with high accuracy.

Contribution

It introduces a novel photogrammetric approach validated against medical imaging, allowing automatic extraction of features to distinguish instrument modifications.

Findings

Achieved sub-millimetre accuracy in mesh validation.

Successfully extracted geometric features to differentiate instrument states.

Demonstrated the method's effectiveness in highlighting morphological differences.

Abstract

Some early violins have been reduced during their history to fit imposed morphological standards, while more recent ones have been built directly to these standards. We propose an objective photogrammetric approach to differentiate between a reduced and an unreduced instrument, whereby a three-dimensional mesh is studied geometrically by examining 2D slices. Our contribution is twofold. First, we validate the quality of the photogrammetric mesh through a comparison with reference images obtained by medical imaging, and conclude that a sub-millimetre accuracy is achieved. Then, we show how quantitative and qualitative features such as contour lines, channel of minima and a measure of asymmetry between the upper and lower surfaces of a violin can be automatically extracted from the validated photogrammetric meshes, allowing to successfully highlight differences between instruments.