Source code for Fitting Ellipses

April 2015

We are interested in creating computer-based tools to help design engineers during the first stage
of the design process, known as conceptual design. Hence, we develop Sketch-Based Modelling
(SBM) systems. The first stage in our approach for SBM is converting the input sketch into a line drawing.
At this end, we need to determine whether or not every single stroke depicts an elliptic arc.

Attached is a C++ implementation of the code of the new Fitting Ellipses (FE) algorithm.

You can download the FE code from here.

The input to the FE code is a 2D stroke, which includes
a list of coordinates of points sampled when moving the cursor.
The time interval is also stored (as it is used for some finding corners approaches).

The output is the information of the elliptic arc that better fits the stroke.
The information is stored in an instance of the class CArc, where every Arc instance includes:

double Centre_x, Centre_y
double Radius_a, Radius_b; // The semi-axes lengths
double Rotation; // Counterclockwise angle of rotation from the x-axis to the major axis
double Focus1_x, Focus1_y
double Focus2_x, Focus2_y
double StartAngle; //Relative to the local system. Absolute angle is StrarAngle+Rotation
double EndAngle; //Relative to the local system. Absolute angle is EndAngle+Rotation

The figure of merit of the fitting is also returned (1 is perfect fit and 0 is no fit at all).

The approach is encapsulated into a main class CFitEllipse. Complementary code is also provided.

Reader must note that the fitting ellipses approach includes detection of corner points.
The algorithms used to detect corner are provided as black boxes.

This approach for fitting ellipses is extensively described in:

Company P., Plumed R. and Varley P.A.C. (2015).
A fast approach for perceptually-based fitting strokes into elliptical arcs.
Computer Graphics International 2015, to appear.

To help understanding how the code works, and in order to offer a test environment too, the following main
file is also provided:

· FitEllipseMain.cpp, and its header FitEllipseMain.h.

This main function reads data contained in an example named as “example.stk”.
Other examples are provided in the corresponding folder.

Finally, we must highlight that the code was written to make it readable. Efficiency never was a goal.

********************************************************************************************

The FE code is free software. But if you find it useful for your own research,
please cite our paper:

Company P., Plumed R. and Varley P.A.C. (2015).
A fast approach for perceptually-based fitting strokes into elliptical arcs.
Computer Graphics International 2015, to appear.

********************************************************************************************