This is the accepted version of the paper.This version of the publication may differ from the final published version. trauma, and exposure to damaging noise, the most common treatment is a hearing aid. Since a patient typically uses a hearing aid for many hours during the day, it must be comfortable to wear. Permanent repository linkHearing aids are typically custom-made to match the three-dimensional (3D) geometry of the patient's ear in order to achieve a comfortable fit.This article presents a software-based approach to interactive 3D shape modeling for geometric design of hearing instruments. We review various shape modeling operations that transform a raw impression to the final shape of the hearing aid device. In addition, we present state-of-the-art methods for automating the design process. HEARING AIDS Anatomical PerspectiveWhen designing a hearing aid, surface manipulations are often carried out with respect to anatomical features of the ear. In Figure 1 (a) and (b), we simultaneously an image of a right ear along with an impression (described below) to show the major relevant features. The canal is topmost portion of the surface and is the part that goes inside the ear canal. The aperture is a plane that separates the inner ear and the outer ear. The tragus is the small flap of cartilage near the aperture. Across from the tragus is the anti-tragus. The tragus and anti-tragus are protrusions of the ear geometry so they appear as indentations on the impression. Between the tragus and antitragus is the notch. Also near the aperture, the concha is the bowl-shaped cavity that appears as a hump on the impression. The crus is a ridge of cartilage on the ear and appears as a valley on the impression. The cymba is an indented region next to the crus, while the anti-cymba is the flap of cartilage above the cymba in the picture of the ear. On the impression, the cymba is a protrusion and the anti-cymba is an indentation. Please see Gray's anatomy [1] for more details.

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Abstract. We propose a shape descriptor for 3D ear impressions, derived from a comprehensive set of anatomical features. Motivated by hearing aid (HA) manufacturing, the selection of the anatomical features is carried out according to their uniqueness and importance in HA design. This leads to a canonical ear signature that is highly distinctive and potentially well suited for classification. First, the anatomical features are characterized into generic topological and geometric features, namely concavities, elbows, ridges, peaks, and bumps on the surface of the ear. Fast and robust algorithms are then developed for their detection. This indirect approach ensures the generality of the algorithms with potential applications in biomedicine, biometrics, and reverse engineering.