CN101459901B - Vector map data transmission method based on multi-level slicing - Google Patents

Abstract

The invention discloses a vector map data transmission method based on a multi-level slicing method, the steps of which are as follows: (1) performing L (L=1, 2, ..., m) level 4 equal divisions on the map to obtain L level A square area, and then classify the features that intersect the square area and have a weight level of L or a pairing level into a data set called a "multi-level slice". (2) The map data transmission from the server to the mobile terminal takes multi-level slices as the basic unit. (3) After the mobile terminal receives the multi-level slices, it first integrates the elements of each level of the slices and their ancestor slices, and then stitches the slices into a complete map of the target area of the mobile terminal. (4) The mobile terminal caches multi-level slices. Each update first retrieves multi-level tiles from the local cache, or asks the server if it is not local. The advantage of the present invention is that the mobile terminal side can reuse the local cached map data in a high proportion, thus effectively reducing the traffic of map data transmission.

Description

Vector map data transmission method based on multi-level slicing

technical field

The invention mainly relates to the field of geographic information systems, in particular to a vector map data transmission method based on multi-level slicing.

Background technique

With the rapid development of wireless communication technology, Location-based Service (LBS) is expected to become a killer application. The LBS application system consists of a server, a mobile terminal and a wireless communication network connecting the two. Mobile terminals have the characteristics of small screen, short continuous power supply time, less storage resources, and low CPU computing power. There are problems such as channel instability and low bandwidth in wireless communication networks.

The online transmission of map data in the LBS application system can provide users with real-time information that meets individual needs and is rich in content, and there is no pre-stored map set in the mobile terminal, which does not require user update and maintenance. However, online transmission of map data faces the following problems. First, wireless communication consumes more power, and the power supply of the mobile terminal lasts for a short time. Second, the amount of map data is large, and the wireless network sometimes has unstable channels and low bandwidth.

Compared to raster maps, vector maps contain less data. A vector map is a collection of map elements. The online transmission uses map elements as the basic unit, and there are the following problems: First, every time the mobile terminal enters a new target area, it must send a data request to the server. Even if the local cache has all the data for the new target area, it is impossible to determine this, so the data needs to be retrieved. This increases unnecessary connection times and traffic. Second, the elements sent to the mobile terminal contain all the details, while some details are not used on the small-scale map. This increases data traffic. Third, stripping out unnecessary details from the data body of the elements requires a computationally intensive map automatic synthesis operation.

Contents of the invention

The technical problem to be solved by the present invention is: aiming at the technical problems existing in the prior art, provide a method that can greatly improve the transmission efficiency of vector map data, improve the ability of the mobile terminal to cache and reuse data, thereby reducing the number of mobile terminals and servers. A vector map data transmission method based on a multi-level slicing method for data communication between people.

In order to solve the above-mentioned technical problems, the solution proposed by the present invention is: a vector map data transmission method based on multi-level slicing, which is characterized in that: firstly, multi-level slicing is performed on the vector map data, and the map from the server end to the mobile terminal Data transmission uses multi-level slices as the basic unit, and the mobile terminal will stitch the slices into a complete map after receiving the multi-level sliced vector map.

The generation and stitching steps of multi-level slices are:

A. Generation of multi-level slices:

(1) Slicing: Divide the full map vertically and horizontally into 4 equal slices to obtain the first-level slices; then divide each first-level multi-level slice into four equal slices to obtain the second-level slices, that is, a total of 4 ² =16 slices. ..., and so on, until the m-th slice is generated, for each split, the cut is called the parent slice, and the resulting 4 slices are called sub-slices;

(2) Grading: Divide the map scale into n levels according to the size, in which the scales from level 1 to level n become smaller in turn, divide the map elements into n levels according to the weight, and the n level elements appear on the n level scale The elements in the map that do not appear in the n-1 level scale map establish a correspondence between the scale level and the multi-level slice level, and group the elements of a certain level that intersect with a certain level of slice into a group, which is called this grouping. L-level slice, and say that this group of elements belongs to the slice; at the same time, define the brother slice of a certain level slice, and the S-level brother slice refers to the set of S-level elements that intersect with the corresponding area of the L-level slice, where S=1, 2,...,L-1; the S-level parent slice refers to the ancestor slice or parent slice whose level is equal to the S-level slice, and the S-level sibling slice is a part of the S-level parent slice;

(3) Increment: The increment of an element is the difference between the detail data of the same element between two scale levels. When the increment exceeds the lower limit of the set ratio compared to the total data of the element, set the increment ;

B. Steps for synthesizing a complete map from multi-level slices:

(1) Multi-level slice retrieval: what is needed to synthesize the map of area A under L-level scale is a set composed of L-level slices intersecting with area A, which is recorded as QSet;

(2) Data integration: For each L-level slice in the QSet, data integration is traced upwards along the sibling relationship of the slice. In addition to the summary of the elements belonging to the slices at all levels, this process also includes the incremental merging of the same element ;

(3) Slice splicing: In the previous step, the data summary of each L-level slice that intersects with the target area A is obtained. The next step is to combine the data summary of these L-level slices according to the spatial proximity relationship, and finally obtain a complete map.

The map data transmission process is:

1) Calculate all the L-level slices that intersect with the area A, and this set is denoted as QSet below;

2) For each L-level slice Q in QSet, perform the following steps:

A. The map application executes the "cache retrieval operation" to check whether the slice Q is cached locally; if the slice Q is already in the local cache, go to step F; otherwise, execute the "extract existing feature record operation" to obtain the slice Q's "terminal existing Element Record";

B. The map application requests the data of the slice Q from the server, and the request information includes the number QID of the slice and the record of the existing elements of the terminal;

C. After the server receives the request, it first calculates the area and level L of the multi-level slice according to the serial number QID, and then the map data service component retrieves the map database to obtain the multi-level slice and its sibling slices, and then according to the existing element records of the terminal, in the retrieval Execute the "remove terminal existing element operation" in the slice, and finally send the multi-level slice and its brother slice to the mobile terminal;

D. The map application receives data, which is a collection of multi-level slices and their sibling slices;

E. Execute the "multi-level slice insertion operation" to store the multi-level slice Q and its brother slices into the local cache;

F. Execute "data integration operation" to generate a complete map dataset of slice Q;

3) All the L-level slices in the QSet are spliced together according to the spatial relationship to obtain a complete map of the region A under the L-level scale.

The local cache on the mobile terminal side is composed of a map element set, an element hash table and a multi-level slice index table; the map element set is composed of various elements in the cache, and each element has an entry in the element hash table, It contains three domains, namely feature ID, reference count, pointer to the storage location of the feature, and the reference count records the number of multi-level slices referencing the feature; the feature hash table is sorted according to the feature ID, each in The local multi-level slice Q has an entry in the multi-level slice index table tree, which contains: (a) multi-level slice number; (b) elder brother chain head pointer, pointing to elder brother slice linked list; (c) pointing to element reference table (d) recently used mark; in the multi-level slice index table, each table item is sorted according to the multi-level slice number.

Compared with the prior art, the present invention has the advantages of:

1. During use, the mobile terminal side can reuse the map data cached locally in the mobile terminal at a high rate, thus effectively reducing the communication traffic of map data transmission. First, when the map is panned, the data for the area (composed of tiles) that persists on the screen is reused. Second, when the map is zoomed out, part of the data used by the large-scale map that appeared earlier will be reused by the smaller-scale map that appears later. The data reuse ratio can reach up to 1/4. Third, when the map is zoomed in, part of the data of the small-scale map that appeared earlier will be reused by the large-scale map that appears later. The latter even only needs to request the server for the map data of the target area under the L+1 scale, and the data of the 1-L scale has been cached locally.

2. The map elements are grouped by square blocks (ie, slices), but the elements are not rigidly divided into multiple parts. The transfer method does not repeatedly transfer features that intersect with multiple tiles at the same time, which helps reduce the traffic of map data transfer.

3. Using multi-level slices as cache units is beneficial to reduce the number of communication connections and data communication volume between the mobile terminal and the server. There are two reasons. First, whenever entering a new area (assumed to be the area A under the L-level scale), it can determine whether all the required data is already in This conclusion is cached locally. If it happens to be overwritten, there is no need to connect to the server to update the data. Second, only part of the details of the elements can be transmitted to the side of the mobile terminal instead of all the details;

4. The multi-level slicing improves the chance of reusing map data on the mobile terminal side, which is beneficial to reduce data communication traffic. . Grouping map elements based on multi-level slices not only maintains spatial proximity but also takes weight into account. In the map display, features with the same weight either appear together or not at all. In this way, multi-level slices have the highest probability of being used together, which is higher than the grouping generated only based on spatial proximity;

5. The method of the present invention can effectively reduce the map data transmission scale and the map processing calculation scale on the mobile terminal side. This method is obviously different from the traditional method, and the data content contained in each slice is more accurate and rich; on the one hand, the data The types are different. The multi-level slices of the present invention are aimed at vector map data. On the other hand, the multi-level slices contain elements with the same weight.

Description of drawings

Fig. 1 is a schematic diagram of multi-level segmentation of vector map data according to the present invention.

Fig. 2 is a schematic flow chart of the map data transmission process of the present invention;

Figure 3-1 is a schematic diagram of the overall structure of the mobile terminal local cache in the present invention;

Figure 3-2 is a schematic structural diagram of a multi-level slice index entry in the present invention;

Fig. 3-3 is the structural representation of element hash table entry in the present invention;

Figure 4-1 is a schematic flow chart of the multi-level slice insertion operation in the present invention;

Figure 4-2 is a schematic diagram of the operation process of slicing elements into the warehouse as the core step;

Figure 4-3 is a schematic diagram of the storage process of brother slice elements;

Fig. 5 is a schematic flow chart of the operation of extracting existing element records in the present invention;

Fig. 6 is a schematic diagram of the system structure applying the method of the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific examples.

(1) The map data transmission from the server to the mobile terminal takes multi-level slices as the basic unit. Multi-level tiles have two meanings. One is a square area in the map, and the other is a set of map elements/increments of the same weight that intersect with the area. The steps to generate multi-level slices are as follows:

1) slice. First, divide the full map vertically and horizontally into 4 equal slices to obtain the first level slice; then divide each level 1 multilevel slice into 4 equal slices to obtain the second level slice (a total of 4 ² =16 blocks);.... . . , and so on, until the m-th slice is generated. For each split, the cut is called the parent slice, and the resulting four slices are called sub-slices.

Multi-level slices are numbered using the following method. First, the four first-level slices are numbered 1, 2, 3, and 4 in the order of upper left, upper right, lower right, and lower left; then, each level-1 slice is equally divided into second-level slices in the same order The numbers are 1, 2, 3, 4; the number of the parent slice followed by the number of the current level is the number of the second-level slice; ..., and so on, the numbers of the other levels of slices can be obtained, such as Figure 1 shows.

2) Grading. First, divide the scale of the map into n levels (among them, the scale of level 1 is the highest, level 2 is the second, ..., level n is the lowest). Correspondingly, the map elements are also divided into n levels according to the weight. Level 1 features are features that appear on level 1 scale maps. A level 2 feature is a feature that appears in a level 2 scale map but does not appear in a level 1 scale map, ..., n level features appear in a level n scale map but do not appear in a level n-1 scale Features in the map. Next, establish a correspondence between the scale level and the multi-level slice level. In practical applications, there must be m≥n, that is to say, there are 4 ^m-n+1 slices of m-n+1 level on a level-1 scale map. For the convenience of description, it is assumed that m=n in this paper, which does not affect the description of the basic principle of the scheme. In this way, the level 1 scale corresponds to the level 1 slice, the level 2 scale corresponds to the level 2 slice, ..., the n level scale corresponds to the n level slice. Finally, the L-level elements that intersect with the L-level slice are grouped together, and this group is called an L-level slice, and this group of elements belongs to this slice. In this paper, the data set of the element to which the L-level slice belongs is also called the L-level slice.

In addition, define the sibling slice of the L-level slice. The S-level (S=1, 2, . . . , L-1) sibling slice refers to a collection of S-level elements intersecting with the corresponding area of the L-level slice. An S-level parent slice refers to an ancestor or parent slice whose level is equal to that of an L-level slice. S-level sibling slices are part of the S-level parent slice. The number of the S-level sibling slice is composed of the number of the L-level slice plus the level S.

3) Increment. In the map display, large features show less detail at higher scales and more detail at lower scales. The increment of a feature is the difference of the detail data of the same feature between two scale levels L, K. The increment of the L-level weight of an element (referred to as the L-level increment) is relative to the increment of all the data used to display the element under the L-1 scale. No matter whether the increment is used or not, there is no perceivable difference in the display effect of the element at the L-1 scale. The increment is only set when the increment compared to the total amount of data of the element exceeds the set ratio lower limit V. This is to ensure that the benefits of the increment outweigh the computational losses. The element increment includes not only the added detail data (some coordinate points), but also the position where the coordinate points are inserted. The delta of an L-level slice consists of the L-level deltas of the higher-weighted features that intersect the slice.

(2) Map data transmission process. When the map application on the mobile terminal needs the map data set R(A, L) of the area A under the L-level scale, the data is obtained through the following steps (see Figure 2):

1) Calculate all L-level slices that intersect with area A, and this set is denoted as QSet below.

2) For each L-level slice Q in QSet, perform the following steps:

A. The map application executes a "cache retrieval operation" to retrieve whether tile Q is cached locally. If the slice Q is already in the local, go to step F; otherwise, execute the "extract existing feature record operation" to get the "terminal existing feature record" of the slice Q.

B. The map application requests the data of the slice Q from the server, and the request information includes the number QID of the slice and the existing feature record of the terminal.

C. After the server receives the request, it first calculates the area and level L of the multi-level slice according to the serial number QID, and then the map data service component retrieves the map database to obtain the multi-level slice and its sibling slices, and then according to the existing element records of the terminal, in the retrieval Execute the "operation of removing existing elements of the terminal" in the received slice, and finally send the multi-level slice and its brother slice to the mobile terminal.

D. The map application receives data, which is a collection of multi-level slices and their sibling slices.

E. Execute the "multi-level slice insert operation" to store the multi-level slice Q and its sibling slices into the local cache.

F. Execute the "data integration operation" to generate a complete map dataset of slice Q.

3) All the L-level slices in the QSet are spliced together according to the spatial relationship to obtain a complete map of the region A under the L-level scale.

(3) The structure of the cache. The local cache on the mobile terminal side consists of map feature sets, feature hash tables and multi-level slice index tables, see Figure 3-1, Figure 3-2, and Figure 3-3. A map feature set consists of individual features in the cache. Each element has an entry in the element hash table, and its data structure is defined as follows:

struct featureHashEntry {

long featureID;

char refCount;

void *featurePtr;

}

Among them, featureID is the feature ID, refCount is the reference count of the feature, and featurePtr is a pointer to the storage location of the feature. The reference count records the number of multilevel tiles that reference the feature. The hash table is hash sorted by feature ID.

Each local multi-level slice Q (excluding sibling slices) has an entry in the multi-level slice index table, and its data structure is defined as follows:

struct TileIndexEntry{

long tileID;

void *brotherListHead;

void *featureRefListPtr;

char used;

}

Among them, tileID is a multi-level slice number; brotherListHead field stores the head pointer of the brother chain, which is used to point to the brother slice list; featureRefListPtr field stores the pointer to the feature reference table; used field is the most recently used mark. The usage of the recently used flag is: every time it is used, it will be incremented by 1; every certain period T, it will be cleared to 0. When a slice needs to be eliminated, the slice whose used field value is 0 becomes a candidate.

Assuming that the level of slice Q is L, the linked list of sibling slices has a total of L-1 nodes, corresponding to 1, 2, ..., L-1 sibling slices in sequence from the beginning to the end. Each node contains feature reference table. The feature reference table consists of pointers to feature hash table entries. The elements pointed to by these entries are the elements to which the L-level slice Q or the sibling slice belongs.

In the multi-level slice index table, each table item is sorted according to the multi-level slice number. Enter the serial number of the multi-level slice, search the sorting table to quickly determine whether the multi-level slice is already in the local, and use the element reference table and sibling slice linked list to immediately obtain the data of the multi-level slice and the element to which the sibling slice belongs.

(4) Cache retrieval operation. Enter the number QNo of the slice, and the steps to retrieve the slice are:

1) In the multi-level slice index table, use the binary search method to find the number QNo. If not found, return the conclusion that the slice does not exist, and the search ends.

2) Obtain the element reference table and the head pointer of the brother slice chain from the found table item. From the former, the elements (including increments) to which the slice belongs can be obtained. From the latter, the element to which each sibling slice belongs can be obtained.

3) Execute "data integration operation" on the slice and its brother slice to get the complete map data of the L-level slice.

(5) Multi-level slice insertion operation. Each time a multi-level slice (and its sibling slice) is received, the insert operation is performed. Multilevel slices and sibling slices can be identified by their respective numbers. Insert operation steps are as follows (see Figure 4-1, Figure 4-2, Figure 4-3):

1) Insert a table item QEntry in order in the multi-level slice index table.

2) Allocate an element reference table, pointed to by the element reference table pointer of QEntry.

3) Execute the operation of warehousing elements of slices. Steps include:

A. Allocate element reference table, the number of entries is equal to the number of elements in the slice.

B. For each element of the slice,

If the feature content only contains the feature ID (meaning the feature data is already in the cache), perform the following steps:

a) With the feature ID as input, retrieve the feature hash table entry in the feature hash table.

b) The reference count in the hash table entry is incremented by 1.

c) Use the element reference table item to point to the element hash table item.

Otherwise (feature content contains complete feature data), perform the following steps:

a) Store the features in the map data cache.

b) Apply for an element hash table entry, and use this entry to point to the storage location of the element.

c) The reference count of the hash table entry is set to 1.

d) Use the element reference table item to point to the element hash table item.

4) For elder slices, perform the following steps in descending order of levels:

A. Allocate sibling nodes, which contain element reference tables.

B. Execute the operation of warehousing the elements of the slice, the process is the same as that described in step 3.

C. Add the sibling node to the tail of the sibling list.

6) Cache elimination operation. The cache adopts the LRU strategy to eliminate multi-level slices. The recently used flag of the multi-level slice index entry is used to record the most recently used multi-level slice. After the cycle time T, the multi-level slices that have not been marked as recently used will be eliminated. The steps to eliminate the L-level slice Q are as follows:

1) For each entry in the element reference table of slice Q, decrement the reference count in the element hash table item it points to by 1. If decremented to 0, the hash table entry and the feature storage it points to are freed. Release the feature reference table.

2) For each node of the sibling list, perform the same action as step 1.

3) Delete the entry corresponding to the slice Q in the multi-level slice index table.

(7) Extract the existing element record operation. When the mobile terminal requests the data of the slice Q from the server, it will perform the "extract existing element record operation" to obtain the elements that can be reused locally, and the server will no longer transmit the data of these elements. The operation steps of extracting existing element records are as follows (see Figure 5):

1) Retrieve the ancestor slices of slice Q in the local cache. The search starts from level L-1, and goes up step by step until the ancestor slice is encountered (the level is recorded as S _min ) or the search is completed (let S _min =0).

2) Retrieve the four sub-slices of the slice Q in the local cache to obtain the local set LocalChildSet.

3) Retrieve the L-level slices (a total of 8 blocks) adjacent to the multi-level slice Q in the local cache, and obtain the local set LocalNebSet.

4) Generate the content of the existing data record of the terminal, including the level S _min of the existing parent slice, the number of the sub-slice already in the terminal, and the number of the adjacent slice already in the terminal.

(8) Remove the existing element operation of the terminal. Before returning the data of the slice Q to the mobile terminal, the server removes the existing elements of the terminal according to the existing element records of the terminal. The actual action of removal is to leave the feature ID and discard other parts. The operation steps to remove the existing elements of the terminal are as follows:

1) According to the existing parent slice level S _min , remove the elements belonging to the 1-S _min sibling slices of the slice Q.

2) According to the number of the sub-slice already in the terminal, for the slice Q and its brother slice, if the element in it intersects with the local sub-slice, the element is removed.

3) According to the numbers of adjacent slices already at the terminal, remove elements that intersect with slice Q and adjacent slices at the same time.

(9) Data integration operation. For each L-level slice Q in QSet, data integration is both a summary of elements and an incremental merging. Specific steps are as follows:

1) Add the slice Q to the linked list TList. Let G = slice Q.

2) If the slice G is not level 1, add the brother slice of G to the head of the slice linked list TList.

3) Let G=G's superior slice, go to step 2 until the level of G reaches level 1.

4) Traverse the slice linked list TList from the beginning to the end, and for each slice, summarize its elements into the integration result, and merge the increment into the corresponding elements.

(10) A system for transmitting multi-level slices. The system applying the present invention is composed of a server and a mobile terminal, and the two are connected together through a communication network, as shown in FIG. 6 . The components of the server include map data service components and vector map database. One of its main functions is to send multi-level slices (including elder slices) to mobile terminals. Multi-level slices can be pre-stored in the database or dynamically generated.

The side of the mobile terminal includes a map application, a cache manager and a multi-level tile cache set. The Cache Manager manages and maintains a set of multi-level tile caches for map applications to retrieve and read multi-level tiles. All multilevel tiles received from the server will be stored in the multilevel tile cache set.

Each time a mobile terminal initiates a map data request for multi-level slices, it will be accompanied by a record list of existing elements of the terminal. After the server receives the request, the map data service part retrieves the map database, obtains the required slice and its brother slice, then removes the elements already in the terminal according to the existing element record table of the terminal, and finally sends these slices to the mobile terminal.

Claims (3)

1. A vector map data transmission method based on multi-level slicing, characterized in that: first the vector map data is multi-level sliced, and the map data transmission from the server end to the mobile terminal takes the multi-level slice as the basic unit, and the mobile terminal After receiving multi-level slices, first integrate the elements of each level of the slice and its ancestor slices, and then stitch the slices into a complete map of the target area; The steps of generating and splicing the multi-level slices are: A. Generation of multi-level slices: (1) Slicing: Divide the full map vertically and horizontally into 4 equal slices to obtain the first-level slices; then divide each first-level multi-level slice into four equal slices to obtain the second-level slices, that is, a total of 4 ² =16 slices. ..., and so on, until the m-th slice is generated. For each slice, the sliced is called the parent slice, and the four slices obtained are called the child slices. The parent slice and the parent and child of the parent slice The higher-level parent slice on the relationship chain is called the ancestor slice of the child slice; (2) Grading: Divide the map scale into n levels according to the size, in which the scales from level 1 to level n become smaller in turn, divide the map elements into n levels according to the weight, and the n level elements appear on the n level scale The elements in the map that do not appear in the n-1 level scale map establish a correspondence between the scale level and the multi-level slice level, and group the elements of a certain level that intersect with a certain level of slice into a group, which is called this grouping. L-level slice, and say that this group of elements belongs to the slice; at the same time, define the brother slice of a certain level slice, and the S-level brother slice refers to the set of S-level elements that intersect with the corresponding area of the L-level slice, where S=1, 2,...,L-1; the S-level parent slice refers to the ancestor slice or parent slice whose level is equal to the S-level slice, and the S-level sibling slice is a part of the S-level parent slice; (3) Increment: The increment of an element is the difference between the detail data of the same element between two scale levels. The element increment includes both the added detail data and the position where the coordinate point is inserted. When When the total amount of data of the increment compared to the element exceeds the lower limit of the set ratio, set the increment; B. Steps for synthesizing a complete map from multi-level slices: (1) Multi-level slice retrieval: what is needed to synthesize the map of area A under L-level scale is a set composed of L-level slices intersecting with area A, which is recorded as QSet; (2) Data integration: For each L-level slice in the QSet, data integration traces back to the first-level slice along the brother relationship of the slice. In addition to the summary of elements belonging to each level of slice, this process also includes the same element Incremental merging of ; (3) Slice splicing: In the previous step, the data summary of each L-level slice that intersects with the target area A is obtained. The next step is to combine the data summary of these L-level slices according to the spatial proximity relationship, and finally obtain a complete map. 2. the vector map data transmission method based on the multi-level slicing mode according to claim 1, is characterized in that the map data transmission process is: 1) Calculate all the L-level slices that intersect with the area A, and this set is denoted as QSet below; 2) For each L-level slice Q in QSet, perform the following steps: A. The map application executes the "cache retrieval operation" to check whether the slice Q is cached locally; if the slice Q is already in the local cache, go to step F; otherwise, execute the "extract existing feature record operation" to obtain the slice Q's "terminal existing Element Record"; B. The map application requests the data of the slice Q from the server, and the request information includes the number QID of the slice and the record of the existing elements of the terminal; C. After the server receives the request, it first calculates the area and level L of the multi-level slice according to the serial number QID, and then the map data service component retrieves the map database to obtain the multi-level slice and its sibling slices, and then according to the existing element records of the terminal, in the retrieval Execute the "remove terminal existing element operation" in the slice, and finally send the multi-level slice and its brother slice to the mobile terminal; D. The map application receives data, which is a collection of multi-level slices and their sibling slices; E. Execute the "multi-level slice insertion operation" to store the multi-level slice Q and its brother slices into the local cache; F. Execute "data integration operation" to generate a complete map dataset of slice Q; 3) All the L-level slices in the QSet are spliced together according to the spatial relationship to obtain a complete map of the region A under the L-level scale. 3. according to claim 1 or 2 described vector map data transmission method based on multi-level slicing mode, it is characterized in that: the local buffer of described mobile terminal side is made up of map feature set, feature hash table and multi-level slicing index table Composition; the map feature set is composed of various elements in the cache, and each element has an entry in the element hash table, which contains three fields, namely element ID, reference count, pointer to the storage location of the element, and reference count Record the number of multi-level slices that refer to the element; the element hash table is hashed and sorted according to the element ID, and each local multi-level slice Q has an entry in the multi-level slice index table tree, which contains: ( a) multi-level slice number; (b) elder brother chain head pointer, pointing to elder brother slice linked list; (c) pointer to element reference table; (d) recently used mark; in the multi-level slice index table, each entry is Multi-level slice numbers are sorted sequentially.

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