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Bug 774 - umeyama sometimes returns a reflection
Summary: umeyama sometimes returns a reflection
Alias: None
Product: Eigen
Classification: Unclassified
Component: Geometry (show other bugs)
Version: 3.2
Hardware: All All
: Normal Unknown
Assignee: Nobody
Depends on:
Reported: 2014-03-27 20:34 UTC by Charles Karney
Modified: 2016-02-11 14:34 UTC (History)
4 users (show)

Patch to umeyama to address reflection bug (1.07 KB, patch)
2014-03-27 20:34 UTC, Charles Karney
no flags Details | Diff

Description Charles Karney 2014-03-27 20:34:40 UTC
Created attachment 445 [details]
Patch to umeyama to address reflection bug

The following code

    const int m = 3;
    const int n = 3;
    Matrix<double, m, n> x, y;
    x <<
      0, 1,-1,
      0, 0, 0,
      0, 0, 0;
    y <<
      0,-1, 1,
      0, 0, 0,
      0, 0, 0;
    Matrix<double, m+1, m+1> ta = umeyama(x, y, false);

returns a matrix with a determinant of -1.  Umeyama's paper doesn't
properly explain how to deal with this case.  Basically everywhere he
says rank(AB^T) = m - 1, he means to say rank(AB^T) < m.  The attached
patch (against version 3.2.1) fixes this bug.  Note that I don't look at
the sign of determinant of sigma at all.  This is too subject to
Comment 1 totto 2016-02-09 14:27:17 UTC
I had the same problem of an unexpected reflection. Searching for the cause I found this bug report with the attached patch which fixed the issue.
Comment 2 Charles Karney 2016-02-09 16:51:47 UTC
You might be interested in bug 771 where I tried to do this fitting problem in a cleaner and more flexible manner.
Comment 3 Gael Guennebaud 2016-02-11 14:27:01 UTC
hm the original code is indeed very odd, and I agree with the proposed patch. (sorry for looking at it so lately).

Since we are at it, I don't see the point of this vector S full of ones... I'll remove it too.
Comment 4 Gael Guennebaud 2016-02-11 14:34:36 UTC
Summary:     Bug 774: fix a numerical issue producing unwanted reflections.

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