OER-3D - Visualization of Sharp Edges

Author: Hubert Mara

Surface based MSII visualization of sharp edges

This cookbook provides the means to visualize the sharpness of cutting edges e.g. from stone tools.

For this task the 2nd MSII feature vector using the surface based integration has to be computed. These filter results relate to mean curvature on dull areas. For angles below 90° there is a jump discontinuity, which correlates with the angle of e.g. a blade. The computation is done with GigaMesh using the commandline.

Citation

This cookbook is best cited by using the initial article about the Multi-Scale Integral Invariant (MSII) filtering:

Mara H, S Krömker, S Jakob, and B Breuckmann (2010). GigaMesh and Gilgamesh 3D Multiscale Integral Invariant Cuneiform Character Extraction. In: VAST: International Symposium on Virtual Reality, Archaeology and Intelligent Cultural Heritage. Ed. by Artusi A, Joly M, Lucet G, Pitzalis D, and Ribes A. The Eurographics Association. ISBN: 978-3-905674-29-3. DOI: 10.2312/VAST/VAST10/131-138

Computation

The required option is the radius for the MSII Filter, which should be 1-2x the width blade grind.

Usefull options are -1 or ---no-volume-integral as we save compute time. Also normals are not needed either --no-normals-file:

gigamesh-featurevectors -1 --no-normals-file -r2.0 10350_GMCF.ply

This will generate three files. One .surface.mat file with the surface based feature vectors and a new plyof the mesh already including these feature vectors. The third file contains technical meta data about the computation as txt.

File import

Open the newly generated ply file containing the MSII feature vector on the command line in the GigaMesh main app: gigamesh 4977_GMOCF_r2.00_n4_v256.surface.ply (or via the GUI).

Alternative: when e.g. both MSII feature vectors were computed and the surface.ply does not exist load the initial file gigamesh 10350_GMCF.ply

Menu File => Import => Feature Vectors (per Vertex) Next choose the file 4977_GMOCF_r2.00_n4_v256.normal.mat

A dialogbox will appear asking Does the first column contain the vertex index? / Recommendation: YES for files computed with gigamesh-featurevectors

Choose Yes

Visualize the feature vectors

Menu Functions => Feature Feature Vector Element Max (or any similar function)

This will show sharp edges as bands next to the edge within the given radius, which is 2.0 in this example.

Improve the rendering

  1. Menu Colorramp => Parula (Jet replacement)
  2. Menu Colorramp => Invert

The image below shows the result. The saturation of the blue color indicates how sharp the edge is. Due to the mathematical properties of the filter the most relevant values are in the orthogonal direction in the distance of the radius from the actual edge.

2nd MSII filter rendering of GdF

Data Source

The stone artifact shown was found in La Grotte De Fumane. The 3D dataset is part of The Open Aurignacian Project and can be downloaded from zenodo.org/doi/10.5281/zenodo.6362149.