Maths - Conversion Matrix to Axis Angle

By: Vladimir Smutny - smutny
Matrix to Axis Angle slight correction
2006-05-10 11:30

Dear Mr. Baker,
I believe that the Java(?) code on the page
http://www.euclideanspace.com/maths/geometry/rotations/conversions/matrixToAngle/index.htm
does not reflect sign analysis done in the table.
When there is some of the vector component close to zero, then sign of the other components depend on the sign of nondiagonal terms which is not reflected in the code. So the relevant part of the code shall probably read instead of
if (xZero && !yZero && !zZero) y = -y;
else if (yZero && !zZero) z = -z;
else if (zZero) x = -x;

but
if (xZero && !yZero && !zZero)
if (!yzPositive) y = -y;
else if (yZero && !zZero)
if (!xzPositive) z = -z;
else if (zZero)
if (!xyPositive) x = -x;

I am not sure about syntax but I am quite positive about the fact (my implementation is in Matlab, so I cannot copy working code).

Best Regards,
Vladimir Smutny

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