Development of a methodology for the reconstruction of the surface of the human foot by videogrammetry

Author(s)

Jose Alberto Provenzano

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Educação Física
• Defense date: 2002-02-26

Examining board members

Ricardo Machado Leite de Barros; Deyse Machado Borges; Sergio Augusto Cunha; René Brenzikofer

• Advisor: Ricardo Machado Leite de Barros

Abstract

The study of the human foot characteristics is an area of great interest in the Biomechanics, the main goal of this study was to develop a methodology for the three-dimensional reconstruction of the points on the surface of the human foot based on videogrammetry. The three-dimensional reconstruction of the human foot, objective of this paper, is performed by starting fiom a structured projection of light on the foot obtaining great density of the points on the surface. Using digital video cameras, the register of the images of the foot is made on this projection. Each marker to be reconstructed was to be registered by at least two cameras, which is a requirement of the three-dimensional reconstruction. For the three-dimensional reconstruction was used the Dvideow software, that developed in the Laboratory of Instrumentation for Biomechanics - UNICAMP. After the image register, it is necessary to know the screen coordinates of alI the points of interest, for this purpose one makes the tracking of the markers in the Dvideo environrnent. The process begins with the definition of algorisms of segmentation of the acquired images. The selection of the algorithms takes place according to the experiments needs end to the images markers size, therefore, may be a variation in the sequence of the algorithm application on the registered images. The algorithms operates in order to alter the intensity of colors, detect the outlines ofthe markers, determine the largest amount ofmarkers for tracking, select the regions of largest contrast of color intensity and select the outlines for the maximum and minimum number of pixels. By executing the automatic tracking of the markers, we obtain the coordinates of the screen (x,y) corresponding to the points on the images. Therefore, we have a pair of images containing the bi-dimensional coordinates of the points. Nevertheless, the order and quantity ofpoints in the sets of data ofboth images are not the same. Then the Matlab software is used to label the points resulting fiom the tracking, that is, in order to let the sets of data which contain the bi-dimensional coordinates have the same amount of points in both sets and also to index the points in the same order. Right after that, in the Dvideow environrnent, the three-dimensional reconstruction of the points is performed on the surface. As a result of the reconstruction, the reconstructed points on the surface of the foot were obtained, whereas, visualization was possible through graphs. Applications of the methodology were made on the feet of three individual and on a model of a foot used as an integrating part of the prothesis of the amputee. Besides that, measurements were made on the mo deI of the foot of distances between points by using the method of videogrammetry and direct measurements between points marked on the surface of the model. For the proposed methodology, the result obtained was: a value for bias of 1.77 mm, for precision of the method of 0.31 mm and an estimated standard error at 1.80 mm. Therefore, conc1uding that the methodology developed in this paper permits a form of three-dimensional reconstruction of the surface of the human foot based on videogrammetry, through which important analytical and biomechanical information is obtained (AU)