Invariant Skin Coordinate System

Project description

The standardization of human anatomical coordinates as a similarity to terrestrial coordinates does not seem to exist, perhaps due to the variability of the human figure, with sex, age, build, and other factors. Recently new approximate 3D models of the human figure such as SMPL-X have been developed for 3D modeling of the human body from a single image, for pose estimation and to capture the expressiveness of the human body. This is not new because there are techniques for 3D modeling of the human body with great precision. The novelty is in doing it from a single image, which allows the modeling of human bodies from photographs taken at any time in history. This is the case of the company that has contracted this project, which has a database with more than 40000 study cases in over a decade of imaging, and the need to establish a coordinate system that allows tracking of skin markers throughout over years of study. The second novelty is to achieve 3D modeling using a single 3D mesh for all study cases. Actually SMPL-X provides three meshes (male, female and neutral).

SMPL-X is based on thousands of 3D scans to train a new unified 3D model of the human body, which extends SMPL with fully articulated hands and an expressive face (link 1 below). This technology is at an early stage but it can already be used to locate any point on the surface of the human anatomy while preserving certain properties such as invariance.

3D modeling from a single image is a fantastic advance, although it does not solve the problem of depth. Smplify-X (link 1 below) is a regressor that uses an optimization algorithm to generate the 3D model from a single pose. SMPL-X and Smplify-X are both used in this project to obtain a localization system on the surface of the human body with invariance characteristics.

The figure above shows three views of the same SMPL-X model optimized for a case study. SMPLX partitions the human body into 20908 very small cells that can be located using a single cell identifier (1 to 20908).

A point on the body surface, or the center of mass of a skin marker, is associated with a single cell, and cell identification can be used to locate the same point in multiple studies over the years. Additionally, it is possible to add the barycentric coordinates of the point for its precise location within the cell. However, the center and right images of the figure above reveal that the 20,908 cells are a sufficiently fine partition to locate the skin marker with sufficient precision. On the other hand, SMPL-X could be assumed as a standard 3D model for the human figure, because it is invariant even between different studies of the same person and between different modeled people. This project has been developed for a major medical company in the United States.

1. https://smpl-x.is.tue.mpg.de/