Calibration-less Anthropometric Scanner Using GPU's

Mario Gazziro, Ph.D.

P. Scotton, H. Bittencourt, A. Osti, F. Cola

University of Sao Paulo - BRAZIL

Anthropometric 3D Scanners Applications

Body Mass Index determinationThe scanner can determine accurately the volume of the patient and (with his weight)could obtain the density d. Using the density value obtained, we can evaluate the percentage of body fat (%BF) using the Siri's equation: %BF = (4.95 / d - 4.50) * 100

d: body density (g/cm3)

Anthropometric 3D Scanners Applications

Postural Analysis AssessmentPostural analysis are used in standing postural measurements in a completely automated way, replacing the symmetry grid by the 3D scanner.

Goals

Developing an Anthropometric 3D Scanner with the following features:

Fast operation, allowing to generate profiles (BMI and Postural Analisys) from large populations in a short time (using GPU acceleration)

Allow it's installation, maintenance and usage by people not specialized in computer graphics (regular technicians from hospitals, clinics and gyms)

Calibration-less challenge

To avoid the usage of calibration patterns in a multi-sensor approach, we try two algorithms to automatic registering the cloud points:

EM-ICP algorithm

Softassign algorithm

Both algorithms could not register point cloud of the human body from different points of view, even with reasonable overlap (about 70 clouds/270o).

Approach: Use only ONE sensor and SLAM techniques to scan the body

* Simultaneous Localization And Mapping

Prototype developed using SLAM

SLAM implementation: KinFu

OpenSource implementation of MicrosofttmKinecttm Fusion API (filters for SLAM)

Supported by PCL pointclouds.org

GPU used to accelerate KinFu

Model: GTX 680

Cuda Cores: 1536

Memory: 2 GB DDR5

PCI Express: 3.0

Architecture: Kepler GK110

NVidia Kepler GK110 Architecture

TSDF Clouds

The cube is subdivided into a set of Voxels. These voxels are equal in size. The default size in meters for the cube is 3 meters per axis. The default voxel size is 512 per axis. Both the number of voxels and the size in meters give the amount of detail of our model.

* pictures and text from from pointclouds.org

TSDF stands for Truncated Surface Distance Function and was first introduced by Brian Curless and Marc Levoy in A Volumetric Method for Building Complex Models from Range Image paper in the Proceedings of SIGGRAPH 1996.

What is the difference between a TSDF cloud and a normal point cloud?

Well, a TSDF cloud is a point cloud. However, the TSDF cloud makes use of how the data is stored within GPU at KinFu runtime.

TSDF Volume Grid in GPU

A representation of the TSDF Volume grid in the GPU. Each element in the grid represents a voxel, and the value inside it represents the TSDF value. The TSDF value is the distance to the nearest isosurface. The TSDF has a positive value whenever we are in front of the surface, whereas it has a negative value when inside the isosurface. The X,Y,Z coordinates for each of the extracted points correspond to the voxel indices with respect to the world model.

Anthropometric Scanner at work

Surface Reconstruction: Poisson

Parameters:Octree Depth factor 10and Solver Divide factor 8

Grid based method,very good automaticresults, but withhuge memory utilization 32 GB RAM in our desktop

Body Mass Index determination

Postural Analysis

* Grant R. Tomkinson *, Linda G. Shaw, Quantification of the postural and technical errors in asymptomatic adultsusing direct 3D whole body scan measurements of standing posture. Gait & Posture, Elsevier, In Press.

Postural Analysis

Jacques Junior, J. et al. Skeleton-based human segmentation in still images. ICIP, 2012.Their algorithm using our skeleton and RGB image to detect posture (red markers)

Conclusions

In december next we will start a protocol with 160 subjects, to evaluate BMI and postural analysis.

The postural analysis will be validatedagainst a specialist visual inspection.

The BMI tests will be validated withrespect to the pletsmography (BOD-POD show in the figure).

Pepper et al. already validate the BMI method with respect to the hidrostatic weighing and DEXA (Dual X-Ray) methods, with an error of 1,5%, usinga 3D scanner from CyberWare and testing 70 subjects.

We will try to improve this results,once our system is faster and have less problems due to breath and movement of the subjects.

Pepper et al., Evaluation of a rotary laser body scanner for body volume and fat assessment. J. Test and Eval, NIH, 2010.

So long and thank you for all the fish!