bundle block adjustment with 3d natural cubic splines

bundle block adjustment with 3d natural cubic splines bundle block adjustment with 3d natural cubic splines

13.07.2015 Views

Calculate the maximum distance between the approximated spline and the originalinput dataWhile(the maximum distance > the threshold of the maximum distance)Add break point to the break point set at the location of the maximum distanceCompare the maximum distance with the thresholdThe larger threshold makes the more break points with more accurate spline to theoriginal input data.N piecewise cubic polynomial functions between two adjacent break points aredefined from the N + 1 break points. There is a separate cubic polynomial for eachsegment with its own coefficients.X 0 (t) = a 00 + a 01 t + a 02 t 2 + a 03 t 3 , t ∈ [0, 1]X 1 (t) = a 10 + a 11 t + a 12 t 2 + a 13 t 3 , t ∈ [0, 1]· · · (2.21)X i (t) = a i0 + a i1 t + a i2 t 2 + a i3 t 3 , t ∈ [0, 1]Y i (t) = b i0 + b i1 t + b i2 t 2 + b i3 t 3 , t ∈ [0, 1]Z i (t) = c i0 + c i1 t + c i2 t 2 + c i3 t 3 , t ∈ [0, 1]The strength is that segmented lines represent a free-form line with analytical parameters.The number of break points is reduced and the input error should be absorbedby a mathematical model especially in the expression of points on a straight line. Anatural cubic spline is data independent curve fitting. The disadvantage is that theentire curve shape depends on all of the passing points. Changing any one of themchanges the entire curve.28

Cardinal splineA Cardinal spline is defined by a cubic 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 cubicHermit spline is continuity C 1 that the first derivatives are equal at break points. Adisadvantage of a cubic 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 with 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 withineach segment. The advantage is no need for tangents but the disadvantage is theimprecision of the tangent approximation.29

Calculate the maximum distance between the approximated spline and the originalinput dataWhile(the maximum distance > the threshold of the maximum distance)Add break point to the break point set at the location of the maximum distanceCompare the maximum distance <strong>with</strong> the thresholdThe larger threshold makes the more break points <strong>with</strong> more accurate spline to theoriginal input data.N piecewise <strong>cubic</strong> polynomial functions between two adjacent break points aredefined from the N + 1 break points. There is a separate <strong>cubic</strong> polynomial for eachsegment <strong>with</strong> its own coefficients.X 0 (t) = a 00 + a 01 t + a 02 t 2 + a 03 t 3 , t ∈ [0, 1]X 1 (t) = a 10 + a 11 t + a 12 t 2 + a 13 t 3 , t ∈ [0, 1]· · · (2.21)X i (t) = a i0 + a i1 t + a i2 t 2 + a i3 t 3 , t ∈ [0, 1]Y i (t) = b i0 + b i1 t + b i2 t 2 + b i3 t 3 , t ∈ [0, 1]Z i (t) = c i0 + c i1 t + c i2 t 2 + c i3 t 3 , t ∈ [0, 1]The strength is that segmented lines represent a free-form line <strong>with</strong> analytical parameters.The number of break points is reduced and the input error should be absorbedby a mathematical model especially in the expression of points on a straight line. A<strong>natural</strong> <strong>cubic</strong> spline is data independent curve fitting. The disadvantage is that theentire curve shape depends on all of the passing points. Changing any one of themchanges the entire curve.28

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