Pierre Baret Personal Website

DRAWING TRACK

In short

For a school project, I imagined and prototyped with 3 friends a computer assisted drawing system based on an OptiTrack. The idea was to provide a system able to capture a drawing on a computer without changing the artists' favorite tools : paper and pen.

About the project

This project was part of the courses about Post-WIMP interactions at Grenoble INP - ENSIMAG. This courses focuses on Human-Computer interactions other than Windows, Icons, Menus and Pointing device (WIMP).

For this project, we had to chose an interesting subject, do the research and develop a prototype using the availiable tools and materials of the school's fablab.

The software for the prototype was developped under Ubuntu with C++ using the Optitrack SDK, Qt and the Point Cloud Library.

THE PROTOTYPE

Installation

The pen and the support are tracked by 3 optitrack cameras thanks to motion capture markers (forming what we call "rigid bodies"). A video projector is used to project the recorded drawing on the paper.

My main contributions of the project were the making of the support for the paper sheet and the pen and the elaboration of a calibration procedure for the pen rigid body.

Pen Calibration

The calibration procedure was indeed required to get the transformation between the center of the pen rigid body (3D position captured by the optitrack) and the real position of the tip of the pen (that we needed to track the drawing). The idea that I had was to make the pen point to a fixed point on the support, turn the pen around this point without moving the pen tip from the support.

The points thus obtained by the optitrack are scattered along a sphere, whose center is the tip of the pen. Estimating the sphere from the cloud of points obtained gives us its center. Linking the center back to the points gives us the transformation we needed. We estimated the sphere using RANSAC algorithm so that we can eliminate outliers and get a quick and precise estimation of the sphere.