Photogrammetric Three-dimensional Modeling and Printing of Cetacean Skeleton using an Omura's Whale Stranded in Hong Kong Waters as an Example

Summary

The bone morphology of a semi-degreased baleen whale was documented by photogrammetry with a DSLR camera to generate three-dimensional (3D) models by computer, which were 3D printed as half-sized replicas of the original for display and educational purposes.

Abstract

The preparation of cetacean, in particular baleen whale, skeletons presents a great challenge due to their high lipid content and uncommon size. Documentation of the skeletal morphology is important to produce accurate and reliable models for both research and educational purposes. In this paper, we used a 10.8-meter long Omura’s whale stranded in Hong Kong waters in 2014 as an example for the illustration. This rare and enormous specimen was defleshed, macerated, and sun-dried to yield the skeleton for research and public display. Morphology of each bone was then documented by photogrammetry. The complex contour of the skeleton made automated photoshoot inadequate and 3 manual methods were used on bones of different sizes and shapes. The captured photos were processed to generate three-dimensional (3D) models of 166 individual bones. The skeleton was printed half-size with polylactic acid for display purposes, which was easier to maintain than the actual cetacean bones with high residual fat content. The printed bones reflected most anatomical features of the specimen, including the bowing out rostral region and the caudal condylar facet that articulated with Ce1, yet the foramina on the parieto-squamosal suture, which are diagnostic character of Balaenoptera omurai, and an indented groove on the frontal bone at the posterior end of the lateral edge were not clearly presented. Extra photoshoots or 3D surface scanning should be performed on areas with meticulous details to improve precision of the models. The electronic files of the 3D skeleton were published online to reach a global audience and facilitate scientific collaboration among researchers worldwide.

Introduction

Cetacean strandings offer valuable opportunities to learn about their life history, biological health and profile, as well as the effect of anthropogenic actions to the ecosystem. Three-dimensional (3D) representation and modeling allow accurate representation of morphometric measurements that can be used for biomechanical calculations and give insights on various physiological behaviors¹. Morphological adaptations have allowed these animals to survive in the ocean, while some pathologies observed in stranded cetaceans could reveal their biological health and profile, anthropogenic and non-anthropogenic circumstances or cause of death

Protocol

1. Preparation

1. Assemble the semi-degreased whale skeleton.
2. Designate a code for each piece of bone. The code will be used in the photoshoot, 3D model generation, and 3D printing.

2. Photogrammetry

1. Camera and tripod settings
   1. Use a standard lens with focal length of 24-70 mm, diameter of 77-82 mm, and f number of 2.8 L. Avoid wide-angle lenses. Use a compatible tripod with adjustable height of 40-150 cm.
   .......

Discussion

Skeletons for exhibition should be oil-free and odorless. Whale bones are notoriously oily, which makes their preparation exceptionally challenging. A juvenile blue whale stranded in 1998 had its skeletal remains exhibited in the New Bedford Whaling Museum, Massachusetts. Despite tremendous treatment by professionals, the bones remained yellowish with an unpleasant odor, and has been oozing oil continuously for over 20 years²¹. With little experience in handling whales in Hong Kong, great effort w.......

Materials

Name	Company	Catalog Number	Comments
EF 24-70mm 1:2.8 L II USM	Canon	NA	Camera lens
EOS 5DSR	Canon	NA	Camera
ideaMaker 3.6.1	Raise 3D	NA	3D printing software
MVKBFRL-LIVEUS	Manfrotto	NA	Camera tripod
N2 Plus	Raise 3D	NA	3D printer
Agisoft Metashape 1.6.4 (Professional Edition)	Agisoft	NA	3D modeling software
Poly-lactic acid	Raise 3D	NA	3D printing material
Precision 9010 CPU: 2 x Xeon E5-2620 v3	Dell	NA	Computer