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

B-splineThe equation of B-spline with m + 1 knot vector T , the degree p ≡ m − n − 1which must be satisfied from equality property of B-spline since a basis function isrequired for each control points and n + 1 control points P 0 , P 1 , · · · , P n is as [75]C(t) =n∑P i N i,p (t) (2.23)i=owithN i,0 (t) =N i,p (t) ={1 if ti ≤ t ≤ t i+1 and t i < t i+10 otherwiset − t iN i,p−1 (t) +t i+p+1 − tN i+1,p−1 (t)t i+p − t i t i+p+1 − t i+1Each point is defined by control points affected by segments and B-splines are apiecewise curve of degree p for each segment. Advantages of B-splines are to representcomplex shapes with lower degree polynomials while B-splines are drawn closer totheir original control polyline as the degree decreases. B-splines have an inside convexhull property that B-splines are contained in the convex hull presented by its polyline.With an inside convex hull property, the shape of B-splines can be controlled indetail. Although B-splines need more information and more complex algorithm thanother splines, a B-spline provides many important properties than other splines, suchas degree independence for control points.B-splines change the degree of curveswithout changing control points, and control points can be changed without affectingthe shape of whole B-splines. B-splines, however, cannot represent simple constrainedcurves such as straight lines and conic sections.30

2.3.2 Fourier transformFourier series and transform have been widely employed to represent 2D and 3Dcurves as well as 3D surfaces. Fourier series is useful for periodic curves and Fouriertransform is proper for non-periodic free-form lines. Parametric representations ofcurves have been established in many applications. Fourier transform is the generalizationof the complex Fourier series with the infinite limit. Let w be the frequencydomain, then time domain t is described as follow.X(w) = 1 √2π∫ ∞−∞x(t)e −iwt dt (2.24)Discrete Fourier transform (DFT) is commonly employed to solve a sampled signaland partial differential equations. Fast Fourier transform (FFT) which reduces thecomputation complexity for N points from 2N 2 to 2Nlog 2 N improves the efficiencyof DFT. DFT transforms N complex numbers x 0 , · · · , x N−1 into the sequence of Ncomplex number X 0 , · · · , X N−1 .X k =N−1 ∑k=0x n e − 2πiN kn k = 0, · · · , N − 1 (2.25)Shape information can be obtained with the first few coefficients of Fourier transformsince the low frequency covers most shape information. In addition, Fouriertransform can be developed in the smoothing of a 3D free-form line in the objectspace using the convolution theorem with the use of the FFT algorithm.Boundary conditions affect the application of Fourier related transforms especiallywhen solving partial differential equations. In some cases, discontinuities occur dueto the number of Fourier terms used.The fewer terms, the smoother a function.31

2.3.2 Fourier transformFourier series and transform have been widely employed to represent 2D and 3Dcurves as well as 3D surfaces. Fourier series is useful for periodic curves and Fouriertransform is proper for non-periodic free-form lines. Parametric representations ofcurves have been established in many applications. Fourier transform is the generalizationof the complex Fourier series <strong>with</strong> the infinite limit. Let w be the frequencydomain, then time domain t is described as follow.X(w) = 1 √2π∫ ∞−∞x(t)e −iwt dt (2.24)Discrete Fourier transform (DFT) is commonly employed to solve a sampled signaland partial differential equations. Fast Fourier transform (FFT) which reduces thecomputation complexity for N points from 2N 2 to 2Nlog 2 N improves the efficiencyof DFT. DFT transforms N complex numbers x 0 , · · · , x N−1 into the sequence of Ncomplex number X 0 , · · · , X N−1 .X k =N−1 ∑k=0x n e − 2πiN kn k = 0, · · · , N − 1 (2.25)Shape information can be obtained <strong>with</strong> the first few coefficients of Fourier transformsince the low frequency covers most shape information. In addition, Fouriertransform can be developed in the smoothing of a 3D free-form line in the objectspace using the convolution theorem <strong>with</strong> the use of the FFT algorithm.Boundary conditions affect the application of Fourier related transforms especiallywhen solving partial differential equations. In some cases, discontinuities occur dueto the number of Fourier terms used.The fewer terms, the smoother a function.31

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