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Bug 1713 - Comparison between two quaternions modulo 2*pi
Summary: Comparison between two quaternions modulo 2*pi
Status: NEW
Alias: None
Product: Eigen
Classification: Unclassified
Component: Geometry (show other bugs)
Version: 3.3 (current stable)
Hardware: All All
: Normal Wrong Result
Assignee: Nobody
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Reported: 2019-05-14 00:56 UTC by Vincent Samy
Modified: 2019-12-04 18:38 UTC (History)
4 users (show)


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Description Vincent Samy 2019-05-14 00:56:12 UTC 
Hello,

So i bumped into a problem with quaternion function `isApprox` that tells whether or not two quaternions are the same. Though, quaternions can represent the same rotation and have different values. Here is the code.

Eigen::Quaterniond q1 = Eigen::Quaterniond::UnitRandom();
Eigen::Quaterniond q2(-q1.w(), -q1.x(), -q1.y(), -q1.z());
q1.isApprox(q2); // return false
q1.angularDistance(q2); // return 0

q1 and q2 represent the same rotation (modulo 2*pi), maybe the function should return true?

Best,

Vincent S.
Comment 1 Nobody 2019-12-04 18:38:22 UTC 
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