Combined Dynamic Virtual Spatiotemporal Graph Mapping for Traffic Prediction Yingming Pu Westlake University China

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Combined Dynamic Virtual Spatiotemporal Graph Mapping for Traffic Prediction
Yingming Pu
Westlake University, China
puyingming@westlake.edu.cn
Abstract
The continuous expansion of the urban construc-
tion scale has recently contributed to the demand
for the dynamics of traffic intersections that are
managed, making adaptive modellings become a
hot topic. Existing deep learning methods are pow-
erful to fit complex heterogeneous graphs. How-
ever, they still have drawbacks, which can be
roughly classified into two categories, 1) spatiotem-
poral async-modelling approaches separately con-
sider temporal and spatial dependencies, resulting
in weak generalization and large instability while
aggregating; 2) spatiotemporal sync-modelling is
hard to capture long-term temporal dependen-
cies because of the local receptive field. In or-
der to overcome above challenges, a Combined
Dynamic Virtual spatiotemporal Graph Mapping
(CDVGM) is proposed in this work. The con-
tributions are the following: 1) a dynamic vir-
tual graph Laplacian (DV GL) is designed, which
considers both the spatial signal passing and the
temporal features simultaneously; 2) the Long-
term Temporal Strengthen model (LT 2S) for im-
proving the stability of time series forecasting;
Extensive experiments demonstrate that CDVGM
has excellent performances of fast convergence
speed and low resource consumption and achieves
the current SOTA effect in terms of both accu-
racy and generalization. The code is available at
https://github.com/Dandelionym/CDVGM.
1 Introduction
Traffic flow forecasting is a fundamental intelligent trans-
portation task that requires predicting the traffic flow in all
interactions of a road map [Rao et al., 2022; Tedjopurnomo
et al., 2020; Nagy and Simon, 2018; Medina-Salgado et al.,
2022; Jiang and Luo, 2022; Tang and Zeng, 2022]. Traffic
flow forecasting subsumes a series prediction task, as the flow
of a road network can be thought of as a set of nodes’ tempo-
ral series prediction task. Therefore, it is a more challenging
task than time series prediction by requiring both spatial-level
modelling and temporal-level prediction because of the com-
plex dependencies of spatial dimensions.
Figure 1: General topology-based methods utilize a fixed road map
to represent spatial connection or dynamics aggregated with the road
map as spatial connection(left), which is built on the assumption
that there is no indirect societal level of connection; Our dynamic
virtual spatiotemporal graph (right), has the ability to model low-
high-dimension-oriented dependencies without topological informa-
tion adaptively.
Recently, significant progress has been made to address
the topology-based traffic prediction task [Chen et al., 2022;
Wang et al., 2022a]. However, the topological structure of a
graph can be dynamically changing in the real world and the
traffic crash can lead to unavailable crossroads. Latest meth-
ods such as DGCN [Guo et al., 2022], DCRNN [Li et al.,
2017], STFGNN [Li and Zhu, 2021]and S2TAT [Wang et al.,
2022b]have significantly improved the fitness of spatiotem-
poral modelling. However, on the one hand, their competitive
result still relies on topological connections that are not adap-
tive enough due to traffic jams or crashes, as shown in Fig 1.
On the other hand, it is generally confused whether it is better
to use the space-time asynchronous method or the space-time
synchronization method because both of them have their ad-
vantages, for example, a synchronous method such as AST-
GCN [Guo et al., 2019a]and DCRNN [Li et al., 2017]of-
ten have the weakness of local receptive field, which lead to
the shortage of modelling long-term dependencies and asyn-
chronous methods such as STFGNN [Li and Zhu, 2021]and
S2TAT [Wang et al., 2022b]lack the ability of dependency’s
arXiv:2210.00704v1 [cs.LG] 3 Oct 2022
representation because the spatiotemporal graph structure in-
herently has the complex coupling in both spatial and tempo-
ral dimensions. To our knowledge, existing methods hardly
take into account each of the important conditions mentioned
above simultaneously because of the consideration of com-
putational complexity or inference speed or even modelling
ability.
To overcome these shortages, the Combined Dynamic Vir-
tual spatiotemporal Graph Mapping (CDVGM) is proposed.
In this work, we explore capturing dynamic correlations be-
tween spatial and temporal dimensions without any topolog-
ical additions and the stability of the prediction. The work
draws on cross-entropy theory and uses it as the basis for the
asymmetric study of node correlations in the construction of
dynamic Laplacian. In this work, all traffic nodes are located
in the same quantifying space to compute the differences by
cross-entropy of history flow data. We treat the result as the
expression of correlations of each two nodes in the case of
incorporating temporal features. Therefore, the direction is
also addressed as there are up-streams and down-streams ob-
jectively in the road of the real. Unlike existing methods, CD-
VGM efficiently generates adaptive Laplacian through his-
tory flows in a series of states even if the road network is
changing, e.g. some interactions might be unavailable due to
the crash. Finally, we find that the graph Laplacian operators
with different order of magnitude scales can better represent
the key nodes in the spatial network and find the high-energy
regions existing in the corresponding road network, which is
more conducive to the transmission of induced graph signals.
Besides, the stability of the mid-range forecasting problem
also got relief by the way of LT 2Smodule, which takes the
trend as the key of the prediction task and improves the whole
accuracy even in complex couplings of spatiotemporal depen-
dencies.
1) The first topological-structure-free framework with dy-
namic dependencies modelling is proposed, which com-
bined both synchronous and asynchronous advantages
within fast convergence speed and excellent prediction
accuracy.
2) The Laplacian is carefully designed by a dynamic vir-
tual graph for graph signal passing, which considers the
temporal correlations and spatial connections simultane-
ously in a time-series-based way by similarity theory.
3) A Long-Term Temporal Strengthen (LT 2S) module is
proposed to enhance the perception of long-range de-
pendencies with flexibility. It gives a simple but effec-
tive way to the series prediction task.
4) Extensive experiments on four benchmarks demonstrate
that the proposed framework outperforms many recent
state-of-the-art methods, implying that CDVGM has the
best predictive ability and application value so far.
2 Related works
2.1 Traffic Prediction
Traffic forecasting has many application values in smart city
construction. Traffic data is often viewed as a spatiotemporal
graph. Due to the limited modelling ability of the early sta-
tistical methods [Junior et al., 2014], they only consider the
temporal dimension for modelling, ignoring the geographic
effect of the spatial dimension, which leads to the funda-
mental defects of such methods. Subsequently, STGCN [Yu
et al., 2017a]and DCRNN [Li et al., 2017]model the spa-
tial dimension through a deep learning method with GLU or
RNN for temporal prediction asynchronously while methods
such as STSGCN [Song et al., 2020]and STFGNN [Li and
Zhu, 2021]use a local graph to represent spatiotemporal cor-
relation synchronously. S2TAT [Wang et al., 2022b]uses a
time-oriented graph convolution network to improve the abil-
ity of spatiotemporal perception. Owing to the challenges
of spatiotemporal modelling, attention mechanism is adopted
such as ASTGCN [Guo et al., 2019a]and DGCN [Guo et al.,
2022]etc. Except this, STGODE [Fang et al., 2021]uses
spatial-based adjacency matrices and semantic-based adja-
cency matrices to reflect spatial dependencies, and perceive
high-dimensional spatiotemporal correlations through ordi-
nary differential equations. ST-3DNet [Guo et al., 2019b]
first utilizes a 3D-convolution operator for spatiotemporal
graph modelling and ST-ResNet [Zhang et al., 2017]consid-
ers the fact of temporal characteristics of crowd movement to
fit the real-world situation better.
In a word, existing methods normally either consider the
complex coupling as a separate modelling problem wrongly
within the IID assumption or ignore the direct or indirect en-
tanglement that exists between potential spatiotemporal de-
pendencies, which leads to the drawbacks of low general-
izability. Unlike prior works, our novelty is that propos-
ing a topological-free virtual graph designed by combining
spatiotemporal dimensions and equipped with a temporal
strengthen strategy asynchronously to boost performance for
the prediction task.
2.2 Graph convolutional neural network
The graph convolutional neural network realizes the opera-
tion of convolution of non-Euclidean graph data, and GNN
has had a significant impact in the fields of social relation-
ship mining and chemical biology. It can be roughly divided
into two categories, one is a spectral graph neural network
based on spectral graph theory, and the other is a graph net-
work based on the spatial method. Among them, ChebyNet
[Defferrard et al., 2016]uses Chebyshev polynomials to ap-
proximate the Laplacian operator of spectral graph decompo-
sition, which greatly reduces the computational complexity
and is a typical representative of spectral graph neural net-
works. Then graph convolution neural network (GCN) [Kipf
and Welling, 2016]simplifies ChebyNet with a first-order
polynomial, which removes the hyperparameter of K-level
adjacent and becomes the cornerstone of spatial graph neu-
ral network. Space-based GCN generalizes convolution in
Euclidean space to work on graph data. For example, Graph-
SAGE [Hamilton et al., 2017]transmits the neighbour node’s
signal through an adjacency matrix before aggregating fea-
tures, and Graph Attention Network (GAT) [Velickovic et al.,
2017]weight node signals by attention mechanism. Simpli-
fied Graph Convolution Network (SGC) [Wu et al., 2019]re-
moves the non-linear activations in hidden layers for local av-
摘要:

CombinedDynamicVirtualSpatiotemporalGraphMappingforTrafcPredictionYingmingPuWestlakeUniversity,Chinapuyingming@westlake.edu.cnAbstractThecontinuousexpansionoftheurbanconstruc-tionscalehasrecentlycontributedtothedemandforthedynamicsoftrafcintersectionsthataremanaged,makingadaptivemodellingsbecomeah...

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