Fitting ellipse equations and other geometric shapes to blobs
Frederick M. Waltz · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1992
The standard technique for estimating the size, location, and angle of rotation of an elliptically shaped blob in a binary image requires the calculation of the first and second moments of the blob. This approach requires that the blob be complete. If only part of the blob is present, this approach gives erroneous results. This paper presents techniques for fitting circles and ellipses to partial blobs using least-squares techniques. In the simpler cases, the solutions are in closed form, so that no iteration is required. In the more difficult problems some of the unknown parameters are eliminated, so that iteration is required on only one or two parameters. Partial- outline fitting techniques are also provided for triangles, squares, and hexagons.