Comparing and combining sliding semilandmarks and weighted spherical harmonics for shape analysis

Area of Science:

• Paleoanthropology
• Comparative Anatomy
• Biomedical Engineering

Background:

• Quantifying morphological variation is crucial for anatomical research.
• Three-dimensional geometric morphometrics (3D GM) using landmarks is a common but time-consuming method.
• Weighted spherical harmonics (SPHARM) offers an alternative for shape analysis.

Purpose of the Study:

• To compare sliding semilandmark and SPHARM analyses for calcaneal shape variation.
• To evaluate a novel combined method, SPHARM-sliding.
• To determine if these methods capture comparable levels of shape variation.

Main Methods:

• Sliding semilandmark and SPHARM analyses were performed on calcanei of gorillas, chimpanzees, and humans.
• A combined SPHARM-sliding method was developed, using SPHARM vertices as initial landmarks.
• Shape variation was quantified using principal component analyses and compared using root mean square (RMS) distances.

Main Results:

• All three methods (sliding semilandmark, SPHARM, SPHARM-sliding) provided comparable 3D shape analyses.
• SPHARM is less time-intensive but captures less detail on sharp edges compared to sliding semilandmarks.
• SPHARM-sliding offers the detail of sliding semilandmarks with an expedited setup.

Conclusions:

• SPHARM is a viable alternative to 3D GM for analyzing small, irregular bones like the calcaneus.
• SPHARM-sliding enhances efficiency while retaining detailed shape analysis capabilities.
• The choice of method depends on the specific research needs regarding detail and time investment.