A device and a method of using the device to determine a user-specific head-related transfer function (HRTF), are described. The device can determine first geometric data corresponding to visible features of a pinna of a user in an image, and second geometric data corresponding to hidden features of the pinna obfuscated by the visible features in the image. The first geometric data and the second geometric data are combined in a geometric model that describes a shape of the pinna, and the user-specific HRTF is determined based on the geometric model. The user-specific HRTF is used to render spatial audio to the user. Other aspects are also described and claimed.