T2TA	Track-to-track association
T2TASB	Track-to-track association with sensor bias
LTGP	Local track geometry preservation
GMM	Gaussian mixture model
EM	Expectation-maximization
NN	Nearest neighbor
GNN	Global nearest neighbor
ML	Maximum likelihood
OSPA	Optimal sub-pattern assignment
CPD	Coherent point drift
${\mathbf{X}}_k^s$	Local tracks from sensor s at time k
K	Total number of discrete time steps
$N_k^s$	Number of tracks at time k by sensor s
${\mathbf{x}}_{t,k}^1$	t-th data from sensor 1 at time k
${\mathbf{x}}_{l,k}^2$	Centroid of the l-th component from sensor 2 at time k
$\mathcal{N}$	Gaussian distribution
${\sigma }_k^2$	Equal isotropic covariance at time k
f	Nonrigid transformation
$\mathbf{I}$	Identity matrix
D	Size of a local track vector
${\pi }_{t,l}^k$	Membership probability of t-th row and l-th column element in ${\pi }^k$ at time k
${\pi }^k$	Membership probability matrix at time k
${\mathbf{Z}}^k$	Indicator matrix
${\mathbf{z}}_t^k$	a $1\times N_k^1$ binary vector for $l=1,2,\dots N_k^2$ at time k
$z_{t,l}^k$	t-th row and l-th column element in ${\mathbf{z}}_t^k$ at time k
${\mathbf{W}}_k$	an $N_k^2\times D$ dimensional weight matrix of the Gaussian kernel
${\mathbf{G}}_k$	an $N_k^2\times N_k^2$ Gaussian kernel matrix
$g_{ij}$	an i-th row and j-th column element in ${\mathbf{G}}_k$
$\beta$	the width parameter in the smoothing Gaussian filter
$\mathbf{Tr}(.)$	Trace of a matrix
$\mathbf{L}$	$N_k^2\times N_k^2$ weighted matrix
$L_{lj}$	a l-th row and j-th column element in $\mathbf{L}$
${\mathbf{G}}_k(i,.)$	i-th row of ${\mathbf{G}}_k$
$\gamma$	Trade-off parameter controlling between Q and $E\left(\mathbf{L}\right)$
${\mathbf{R}}_k$	an $N_k^1\times N_k^2$ matrix
${\mathbf{C}}^k$	Cost matrix of T2TASB at time k as an $N_k^1\times (N_k^2+1)$ matrix
$[x_{t,k}^1,y_{t,k}^1]$	x-axis and y-axis positions of target ${\mathbf{x}}_{t,k}^1$
$[x_{j,k}^1,y_{j,k}^2]$	x-axis and y-axis positions of target ${\mathbf{x}}_{j,k}^2$