Segmentation of Change in Surface Geometry Analysis for Cultural Heritage Applications

Abstract

This work proposes a change-based segmentation method for applications to cultural heritage (CH) imaging to perform monitoring and assess changes at each surface point. It can be used as a support or component of the 3D sensors to analyze surface geometry changes. In this research, we proposed a new method to identify surface changes employing segmentation based on 3D geometrical data acquired at different time intervals. The geometrical comparison was performed by calculating point-to-point Euclidean distances for each pair of surface points between the target and source geometry models. Four other methods for local distance measurement were proposed and tested. In the segmentation method, we analyze the local histograms of the distances between the measuring points of the source and target models. Then the parameters of these histograms are determined, and predefined classes are assigned to target surface points. The proposed methodology was evaluated by considering two different case studies of restoration issues on CH surfaces and monitoring them over time. The results were presented with a colormap visualization for each category of the detected change in the analysis. The proposed segmentation method will help in the field of conservation and restoration for the documentation and quantification of geometrical surface change information. This analysis can help in decision-making for the assessment of damage and potential prevention of further damage, and the interpretation of measurement results.

Segmentation in application to deformation analysis of cultural heritage surfaces

“…In this work, we have tested several approaches to assess the global deformation of the object. The traditional approach of geometry comparison was performed using the comparison method of C2C, C2M, M3C2 and the developed technique of P2P_ProjectionAlongNV [5] and the calculated results were compared. But only in the global geometry comparison, the information regarding the deformation was not clear.…”

“…For the further query to check the local geometry change behavior of the supporting hole, we have performed a changedbased segmentation [5], which is a grouping of similarly behaving change points from the surface and represent it using a simple colormap visualization. In this approach, the missing information that the global geometry comparison could not provide (Figure 3) was also assessed.…”

“…Using the Structured Light (SL) method the 3D model of the object was reconstructed prior to any conservation intervention. Using the recorded model and changed-based segmentation [5], the differences to the shape of the upper supportive part of the globe (Figure .1b) and the lower (Figure .1c) were computed and assessed. The upper part was treated as the reference shape (with the assumption that its shape is the ideal), and the deviation between it and the shape of the lower part was calculated.…”

“…The upper part was treated as the reference shape (with the assumption that its shape is the ideal), and the deviation between it and the shape of the lower part was calculated. The applied global geometry comparison of P2P_ProjectionAlongNV [5] approach failed to provide clear information about the deformation on parts of the object due to the lack of finding corresponding surface points from the changed surface, and the results were affected by the cross-time registration error of the two models. To overcome these issues, we have tried the developed changed-based segmentation method [5] to analyze the deformation.…”

“…The method was sensitive to the resolution of the input data or density of the point cloud. In [5], a changed-based segmentation was shown which could identify the changes on the surfaces irrespective of size, resolution, and noise of the input data. Although the method needed a couple of threshold inputs to classifying surface parts into minor and major change, but the method was promising even to get rid of the cross-alignment issue of the two models if a part of the surface was known to be unchanged.…”