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bundle block adjustment with 3d natural cubic splines

bundle block adjustment with 3d natural cubic splines

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Cardinal splineA Cardinal spline is defined by a <strong>cubic</strong> Hermite spline, a third-degree spline.Hermite form defined by two control points and two control tangents is implied byeach polynomial of a Hermite form. The basic scheme of solving the system of a <strong>cubic</strong>Hermit spline is continuity C 1 that the first derivatives are equal at break points. Adisadvantage of a <strong>cubic</strong> Hermite spline is that tangents are always required while thisinformation is not available for all curves.A Cardinal spline consists of three points before and after a control point and atension parameter. A tangent m i of a cardinal spline is as following <strong>with</strong> given n + 1points, p 0 , · · · , p n .m i = 1 2 (1 − c)(p i+1 − p i−1 ) (2.22)where c is a tension parameter which contributes the length of the tangent. A tensionparameter is between 0 and 1.If tension is 0, a Cardinal spline is referred to asa Catmull-Rom spline[11]. A Catmull-Rom spline is frequently used to interpolatesmoothly between point data in mathematics and between key-frames in computergraphics. A cardinal spline represents the curve from the second point to the lastsecond point of the input point set. The input points are the control points thatdefine a Cardinal spline.A Cardinal spline produces a C 1 continuous curve, nota C 2 continuous curve, and the second derivatives are linearly interpolated <strong>with</strong>ineach segment. The advantage is no need for tangents but the disadvantage is theimprecision of the tangent approximation.29

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