Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
  • G01C21/00—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00
  • G01C21/26—Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 specially adapted for navigation in a road network
  • G01C21/34—Route searching; Route guidance
  • G01C21/3446—Details of route searching algorithms, e.g. Dijkstra, A*, arc-flags, using precalculated routes

Definitions

• the invention relates to a method for determining a minimum cost path between two points of a transport network.
• This type of method is used in particular by road navigation aid systems, intended to determine the lowest cost road route, between an arrival point and a departure point, at a given instant, in order to '' assist a driver of a motor vehicle.
• the cost can be a cost in time, distance, money, road comfort or any other parameter.
• the road network is represented by a plurality of nodes (graphs), linked in pairs by segments corresponding to portions of the road axis (street, road, motorway or other). A cost is assigned to each segment.
• the first algorithm consists in developing a path graph, starting from the starting point and up to the ending point, without knowing a priori the position of the ending point.
• the graph develops concentrically, around the starting point, and therefore has a generally circular shape.
• the respective costs of the different paths are determined simultaneously and the optimal path, of minimal cost, connecting the starting point and the ending point is selected.
• the graph extends over a circular surface, centered around the starting point and with radius R equal to the distance between the starting point and the ending point.
• the surface analyzed is therefore very important. As a result, the computation time is very high.
• the present invention proposes to overcome these drawbacks, in other words to reduce the computation time of a path between two points, through a transport network.
• the invention relates to a method for determining the minimum cost path between two points, through a transport network comprising a plurality of nodes linked in pairs by segments, in which
• - a cost is assigned to each segment of the network, - a path graph is developed, substantially starting from at least one of the two points, and
• the two minimum cost paths are determined, belonging respectively to the two graphs, - and the two minimum cost paths are connected in order to obtain the minimum cost path between the two points.
• the cost can be a cost in time, distance, money, road comfort, or other.
• the invention therefore consists in developing two graphs, starting from the two points respectively, until these two graphs meet, whereas, in the prior art, a single graph was developed from one of the two points, until this graph reaches the other point.
• One thus considerably reduces the surface analyzed and consequently the number of nodes, without increasing the computation time per node.
• one searches for at least two neighboring nodes of said point, one allocates a non-zero basic cost to each of these two nodes and one develops a single graph from these two nodes.
• the basic cost of each node is determined, by proportionality, from the cost of the segment between these two nodes. If a node is inaccessible, for example due to a prohibited direction, it is not taken into account.
• the graph is developed from the nodes located near the point, by assigning to these nodes a non-zero basic cost. This ultimately amounts to developing the graph virtually from the point considered.
• the segments are classified according to a plurality of network levels
• the graph is developed taking into account only the segments belonging to the levels strictly above the level nii nf .
• the development of said graph is started, taking into account all the segments belonging to all the network levels.
• a group of successive segments of a given level m comprising exclusively intermediate nodes not belonging to any segment of level at least equal to m other than those of the group of successive segments of level m considered, and
• an "intermediate" node is a node between the two end nodes of a succession of adjacent segments.
• the invention also relates to a server for assistance with road navigation for implementing the method, comprising an interface for connection to a communication network, a block for receiving requests from client terminals, a block for receiving data from road network, a block for classifying road segments, a block for creating a virtual road network, a block for labeling road segments, a calculation module and an emission block.
• a server for assistance with road navigation for implementing the method, comprising an interface for connection to a communication network, a block for receiving requests from client terminals, a block for receiving data from road network, a block for classifying road segments, a block for creating a virtual road network, a block for labeling road segments, a calculation module and an emission block.
• FIG. 1 shows a diagram of a client terminal connected to a road navigation assistance server, through the Internet;
• FIG. 2 shows a functional block diagram of the navigation aid server of Figure 1;
• FIG. 3 shows a partial view of a road network
• Figures 4 and 5 respectively represent a table of parents and a table of buckets, after the development of a graph through the road network of Figure 3.
• the method of the invention makes it possible to determine the path of minimum cost, here in time, between at least two points, through a road transport network.
• this method is implemented by a server 1 for assistance in road navigation, connected to a communication network 3, here the Internet, and intended to indicate to client terminals, on request from the latter, the minimum cost path to connect a starting point and an ending point through the road transport network.
• a server 1 for assistance in road navigation connected to a communication network 3, here the Internet, and intended to indicate to client terminals, on request from the latter, the minimum cost path to connect a starting point and an ending point through the road transport network.
• the client terminals include cellular telephones which can connect to the Internet 3, by telephone connection to an access provider 5, through a cellular telephone network 4, and communicate via the Internet 3.
• the server 1 comprises an interface 10 for connection to the Internet 3, a block 11 for receiving requests from client terminals, a block 12 for receiving data relating to the road network, a block 13 for classifying road segments, a block 14 creation of a virtual road network, a block 15 for labeling road segments, a calculation module 16 and an emission block 17.
• the reception block 11 is connected, at the input, to the connection interface
• Block 11 is intended to receive requests for determining a road route of minimum cost, between a starting point and an ending point, issued by client terminals. Each request contains an indication of the location of the starting point and an indication of the location of the ending point.
• the receiving block 12 is connected, at the input, to the connection interface
• This block 12 is intended to acquire, via the Internet 3, from supplier servers, not represented, data relating to the road network, including vector mapping data and road traffic information, which is regularly updated.
• the road network map comprises a plurality of nodes, linked in pairs by segments corresponding to portions of road axes. These highways include streets, roads and highways. It will be noted here that the invention also applies to public transport networks, for example by rail, such as a metro network, by sea, such as a ferry network.
• the classification block 13, connected to the creation block 14, is intended to classify the road segments here according to three levels, of index one, two and three, corresponding respectively to streets, roads and highways.
• the index of a level is a function of the size of the road axes of this level. In this case, the higher the level, the larger the size of the road axes of this level.
• the creation block 14, connected to the calculation block 16, is intended to create a virtual road network, comprising here a reduced number of level 3 segments.
• the block 14 searches the road network for groups of successive level three segments such that each group comprises exclusively intermediate nodes not belonging to any level three segment other than those of the group of successive level three segments considered.
• intermediate node is meant to mean that it is a node between the two end nodes of a succession of adjacent segments.
• block 14 substitutes each group of successive level three segments found by a single virtual level three segment, connecting the two end nodes of the succession of segments of the group considered.
• the labeling block 15, linked to blocks 12, 14 and 16 is intended to assign a cost to each segment of the virtual road network and to update this cost regularly, using the traffic information received by the block 12.
• the calculation module 16 comprises a block 160 for developing a graph, a block 161 for detecting a change in the level of segments and a block 162 for determining the path of minimum cost.
• the development block 160 is intended, at the request of a client terminal, to develop two road path graphs, from the starting point and the finishing point respectively, taking into account the state of road traffic, using here a buckets algorithm.
• the buckets algorithm is a graph calculation algorithm.
• the reader can refer to the work "Algorithmes de graphes" by Christian PRINS, Eyrolles editions, second edition 1997, in order to obtain additional information concerning this algorithm.
• the road network contains a plurality of nodes P n , with n varying from 0 to N, linked in pairs by segments. Each segment is associated with a cost. In Figure 3, the road network is partially shown. The cost of each segment between two nodes is indicated in brackets.
• the development block 160 uses two tables, respectively called “parent table” and “bucket table”, respectively represented in FIGS. 4 and 5.
• the parents table includes
• a second column of parent nodes intended to contain, for each node of the network, a parent node associated with this node, - a third column of costs, intended to contain, for each node of the network, the cost of this node, and
• a "parent" node P n 'of a node P n is a node connected to the node P ⁇ by a single segment and located upstream of the node P n along a path of the graph.
• the node P n is in fact a "descending" node with respect to the node P n '. It will be noted that the parent node P n 'can have several descending nodes belonging respectively to several paths of the graph.
• the table of buckets is intended to contain the list of the nodes of the graph, that is to say the nodes selected to be part of the graph, and classified in ascending order in cost, as well as the cost associated with each of these nodes.
• the cost of a node, for a given path corresponds to the cost of the path between this node and the original node of the graph, which is equal to the sum of the costs of the segments forming this path.
• the parent node column and the cost column are initially empty and all flags are initially set to zero.
• the buckets table is initially empty.
• the parents' table contains only the nodes P 0 , ..., Pg, P z , necessary for understanding the description below.
• the nodes adjacent to the node P 0 are the nodes of the network connected to the node P n by a single segment (it is rare that there are several).
• the nodes P 4 , P 2 , P 7 and P 5 are adjacent to the node Po, we select these adjacent nodes and classify them in the table of buckets, with their respective associated costs, in ascending order in cost.
• each node P n of the list For the analysis of each node P n of the list, one seeks and one determines the nodes adjacent to this node P n . Among these adjacent nodes, the node or nodes which have not already been selected are selected. For each adjacent node which has already been selected, the new cost of this node is calculated, taking into account the fact that it belongs to another path (the one passing through the analyzed node P n ). If the new cost of the node considered is lower than its old cost (appearing in the table of parents), we select this node. Otherwise, the node considered is not selected.
• the parent node P n is associated with this node (by substituting the node P n for the old parent node, in the case where the considered node has already been selected) , we indicate the cost of this node (by replacing it with its old cost, in the case where the node considered has already been selected) and we set the flag of this node to one.
• the graph therefore has a substantially circular shape, centered around the point of origin Po-
• the optimal cost path is reconstructed, going up from the node P z to the node Po, from node to node, using kinship relationships between nodes in the parent table. It is thus determined that the path of minimum cost is the path Po - P 7 - »P z .
• the detection block 161 connected to the development block 160, is intended to calculate, as each graph develops, the number of segments of lowest level m inf belonging to the graph considered, to detect the overshoot of d 'a threshold of number of segments of level m inf , and to signal the exceeding of this threshold by the two graphs to the development block 160, so that it continues the development of the two graphs taking into account only the segments belonging to the levels strictly superior to the level mj nf .
• the block 162 for determining the optimal path (that is to say minimum cost), connected to the development block 160, is intended to reconstruct the path of minimum cost, between two nodes, using kinship relationships between nodes in the parent table.
• Points A and B are here each located substantially at the location of a node of the road network.
• classification block 13 classifies the segments of the road network according to the three network levels (street, road, motorway).
• Block 14 then creates a virtual road network, comprising a reduced number of level three segments, as previously explained.
• the labeling block 15 assigns a cost to each segment of the virtual road network and updates this cost regularly, using the traffic information received.
• the cost of a level three virtual segment, corresponding to a group of successive segments of the original road network, is equal to the sum of the costs of the segments of this group.
• a client terminal 2 sends a request to the server 1 for determining the minimum cost path between the starting point A and the ending point B, containing an indication of location of point A and an indication of location of point B.
• the reception block 11 receives the request from the terminal 2, extracts the location indications from the points A and B therefrom and supplies them to the calculation module 16.
• the development block 160 concomitantly develops two path graphs, respectively from the two points A and B, by determining the respective costs of the different paths of each graph, at using the previously explained buckets algorithm.
• the points A and B being located substantially at the location of a node of the network, each point A, B is assimilated to the node located nearby, by assigning a zero base cost to this node.
• Block 160 starts the development of the two graphs using the segments of the three network levels.
• the detection block 161 calculates the number of segments of each graph belonging to the lowest level, namely level one. If the number of level one segments, for the two graphs, reaches a predefined threshold Si, the block 161 detects it and signals it to the development block 160. The latter continues the development of the two graphs, beyond this threshold , using only the segments belonging to levels two and three, strictly superior to level one, and, concomitantly, calculates the number of segments of each graph belonging to the lowest level remaining, namely level two.
• the block 160 detects it and signals it to the development block 161 which continues the development of the two graphs, beyond this threshold S 2 , taking into account only level three segments, strictly greater than level two. It will be noted that if the number of level segments one of one of the two graphs does not reach the threshold Si, the development block 161 develops the two graphs taking account of the three levels, even if the number of level segments one of the other graph reaches and exceeds the threshold S ,.
• the development block 161 interrupts the development of the two graphs.
• the calculation algorithm finds a first point of intersection between C0 and C 1, noted X which is therefore a point which has been chosen by C0 and by C 1.
• V0 [B0]> V0 [X]
• V [Y] V0 [Y] + V1 [Y] and V0 [Y]> V0 [B0]
• V1 [Y]> V1 [B1] We have V [Y]> V0 [B0] + V1 [B1 ] So V [Y]> V0 [X] + VI [X] V [Y]> V [X]
• Block 162 then reconstructs the optimal path between point A and the interference node P, 0 and the optimal path between point B and the interference node P io , using the kinship relationships between nodes in the parent tables, and associate, connects these two optimal paths in order to obtain the minimum cost path between the two points A and B.
• the development block 160 searches for at least two nodes P A , o > PA, I. • • •, forming a segment and between which point A is substantially located.
• Block 160 then assigns to each of the nodes P A o > P AI , • • -, forming a segment, a non-zero basic cost, determined by proportionality from the cost of the segment considered, as explained below.
• P A; n and PA, ⁇ + I two neighboring nodes of point A, forming a road segment on which point A is substantially located.
• the basic cost c (P réelle n ), C (P A, n + i) of each node PA, ⁇ , P A , ⁇ + I is calculated using the following relationships:
• c (P A> n , P A) n + I ), d (P A ⁇ n , P A; n + ⁇ ), d (A, P A , n ) and d (A, P A , n + ⁇ ) represent respectively the cost of the segment connecting P A , n and P A , n + ⁇ , the distance between P A ⁇ n and P A, ⁇ + I> l at distance between P A ⁇ n and A and the distance between P A , n + ⁇ and AT.
• the basic cost of each of these nodes P A ⁇ n is determined , they are selected and they are classified in the array of buckets in ascending order in cost.
• the table of parents we associate with each node P A; n the parent point A, we indicate the cost of this node P A; n and we set its flag to one.
• the send block After determining the minimum cost path, the send block
• the road network could be subdivided into two levels or into more than three levels.
• the navigation aid server creates a virtual network by grouping successive level three segments.
• the navigation aid server could search for groups of successive segments of a given level m comprising exclusively intermediate nodes not belonging to any segment of level at least equal to m (that is to say greater than or equal to m) other than those of the group of segments considered, then substitute each group of successive segments by a single segment of level m.
• the navigation aid server could calculate the number of segments of each graph belonging to the level m inf most bottom and after the number of segments of level m inf , for the two graphs, has reached a predetermined threshold, develop the two graphs taking into account only the segments belonging to the levels strictly higher than the level mj nf , the new lower level taken into account account becoming level m inf + ⁇ .
• the server could repeat this operation, incrementing the lower level as the graphs develop.
• the navigation aid server could be arranged to determine the minimum cost path in terms of distance, money, road comfort or the like.
• the client terminals could connect to the navigation aid server by a communication network other than the global network comprising the Internet and the cellular network.
• the method of the invention could also be implemented by a system other than a navigation aid server and a transport network other than a road network, for example a rail network.

Applications Claiming Priority (1)

Publications (1)

Family

ID=8871164

Family Applications (1)

Country Status (5)

Cited By (1)

Families Citing this family (17)

Family Cites Families (10)

• 2002
  • 2002-01-09 EP EP02711926A patent/EP1463921A1/de not_active Withdrawn
  • 2002-01-09 AU AU2002231861A patent/AU2002231861B2/en not_active Ceased
  • 2002-01-09 CA CA002472950A patent/CA2472950A1/fr not_active Abandoned
  • 2002-01-09 US US10/500,991 patent/US7437239B2/en not_active Expired - Fee Related
  • 2002-01-09 WO PCT/FR2002/000061 patent/WO2003058170A1/fr not_active Application Discontinuation

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events