JP2005525763A - Data stream data compression method and decompression method - Google Patents

Abstract

A method for compressing and decompressing data of various information contents is provided. The data is, for example, topographic nodes and topographic edges or their attribute values. The compression grade can be configured depending on the information content.
The attribute value is omitted for compression, the accuracy of topographic information is limited, or the compression grade is controlled based on the maximum amount of data set.

Description

Prior Art The present invention is based on a data stream data compression method.

  German Patent Publication No. 1010502.7 discloses a route data transmission method. The route data includes nodes in the form of route point data, edges (routes) existing between them, and attribute values belonging to these. The individual path points are connected to each other to form a root corridor, and the data capacity is minimized. The path point data is preferably transmitted sequentially.

  German Offenlegungsschrift 101055897.7 describes a method for exchanging navigation data between a terminal and a central office. Here, the route between the start point and the end point is segmented into partial routes and transmitted. An off-board navigation device according to this method does not calculate route information independently, but queries the server via an appropriate wireless interface. That is, the server transmits route information to the navigation device.

  A method for inputting a destination in a navigation device is known from German Patent No. 10012441. In order to reduce processing costs, only destination names that exist around the current location are recorded. Further, the destinations are classified according to the distance in the destination name list.

Advantages of the present invention The method of the present invention relates to a method for compressing data of a data stream having various information contents. The information content has in particular route data consisting of topographic nodes (path points) and topographic edges (connection paths) and their attribute values. In the present invention, the compression grade can be configured depending on the information content of the data. Here, at the time of compression, at least one of means for omitting the set attribute value, means for limiting the accuracy (for example, coordinate accuracy), and means for setting the maximum data amount and controlling the compression grade accordingly is used.

  Unlike known compression methods that perform compression ignoring the importance of the data and its information content, the present invention interprets the data and eliminates particularly redundant elements from knowledge of the importance.

  The additional data field can also be used arbitrarily in a data format set in accordance with the method of German Offenlegungsschrift 10106502.7 for the transmission of route information, for example.

  The method of the present invention is particularly suitable for compressing route data, but is applicable to all other data. Advantageously, the method of the invention is also suitable for graph-structured data, ie data consisting of polygons of a CAD design including topographic nodes and topographic edges (eg map data).

  The compression method of the present invention is used by a service provider on a server, particularly for an offboard navigation device, and the decompression method (data decoding method) of the present invention is particularly used on a terminal side or a client side.

The dependent claims describe advantageous embodiments of the compression and decompression methods of the present invention. Other advantages of the method of the present invention are listed below.
1. The size of the processing data is reduced, which makes it possible to make good use of the transmission medium at a low data rate.
2. Since the complexity of the compression and decompression algorithms is reduced, it is also suitable for light processor terminals with small working memory.
3. The compression process is strictly sequential. That is, partial data sets can already be stored or transmitted during compression.
4). In a sequential structure of compressed data, the partial data set can be decompressed during transmission.
5. Unlike many other compression methods where a complete table with frequently occurring data elements must be added to the beginning or end of the data, the present invention inserts individual elements only where they are needed, At the time of transmission, the maximum number of data elements is supplied each time.

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the sequential processing of the route graph. FIG. 2 shows a block diagram of a compression process using an associative memory. FIG. 3 shows an attribute value compression method. FIG. 4 shows an example of a route graph.

DESCRIPTION OF THE EMBODIMENTS The method of the present invention is based on the fact that topographic route or map data consists of route points (nodes) and routes (edges) connecting each node. In addition, the nodes and the edges between them include an order in the route data representing the direction from the preferred origin to the destination.

Route points are generally 1. Coordinate 2. Unique identifier (ID)
One or more of the attribute values.

Edges are generally 1. 1. Road name Road class 3. Destination guidance instructions (graphic and / or acoustic)
4). Destination node (route point indication)
5. Travel time Distance 7. Unique identifier (ID)
One or more of the attribute values.

In the data format used, one indicator is defined for each attribute value having large redundancy such as an additionally transmitted ID, a road name, and a destination guidance instruction. The indicator is 1. Data element does not exist (or is equal to the default value) ... NV
2. Data element is equal to the previous one ... Vorgaenger
3. Data element is equal to the xth element → index x continues ... Index
4). The element data value continues ... Explizit
Can take two or more values.

  The indicator for the path point to be transmitted or the indicator for the edge to be transmitted is preferably combined into one bit field.

The compression algorithm proceeds sequentially, in particular iteratively passes through all existing path points (see FIG. 1).
1. After the start step 1 and the allocation step (with the current location as the first route point) 2, the attribute value of the current location is transmitted (step 3).
2. Mark your current location as a leading point (step 4)
3. All edges leaving the current location are preferably iteratively processed from the main route as well (step 5).
3b. The attribute value of the current edge is transmitted (step 6).
3b. Mark current edge as leading edge (step 7)
4). The first one out of the current location or the main route is marked as the preceding edge (step 9).

  In step 8, it is checked whether the current location has further edges. If so, the next edge of the current location is selected as the current edge and the method proceeds to step 6.

  In step 10 it is checked whether further points are present. If not, the method of the present invention ends. If so, the next point is selected as the current point and the method of the present invention is started anew at step 3.

  Original compression is performed when the attribute value is transmitted. Here, the compression algorithm makes full use of the associative memory 27 for each attribute value. One indicator that can take a plurality of index values is defined for each attribute value (see FIG. 2). This value occurs first because the algorithm assigns each attribute value an element number, ie, a point or edge number. That is, for example, “Robert-Bosch street” → 5 means that the road name “Robert-Bosch street” first occurred as the fifth edge. The associative memory 27 is used as a buffer memory and is stored and erased during compression. Instead, an element number in the memory may be assigned to the attribute value. For example, if the corresponding attribute value is input to the memory for the third time, the number is 3. The compression process unit 28 is directly connected to the associative memory 27. The input data is uncompressed route data, and the output data is compressed route data 30.

  Before the original point / edge attribute value is transferred to the compressed data area, an indicator is obtained for each element, and an instruction for the preceding element or an instruction for any other element may be transmitted instead of the value.

  The detailed flow of the individual attribute values of the route points / edges is shown in FIG. According to FIG. 3, it is first checked whether an indicator for the attribute value is defined (step 12). If so, it is checked whether the attribute value is filled or not (step 13). If it is not valid, the indicator is defined as N.V., that is, the attribute value remains empty (step 14). If it is valid, it is checked whether the current attribute value is equal to the attribute value of the preceding element (step 15). If they are equal, the attribute value of the element is defined equal to the attribute value of the preceding element (step 16). If not, it is checked whether “Index” is an allowable value for the current indicator (step 17). If so, it is checked whether a corresponding attribute value exists in the associative memory (step 18). If it exists, an index is defined for the indicator (step 19). If it does not exist, the attribute value or its element number is stored (step 20) and is defined as “Explizit” for processing without compression (step 21). Subsequently, indicators are stored in the memory for the three cases after steps 21, 19, 16, 14 (steps 22, 23, 24), after which attribute values are written (step 25) or element numbers. Is written (step 26).

Similarly, decompression is performed when data is read sequentially. That is, all the route points and edges are repeatedly read out, and the individual route points and edge elements are stored in the table in the order of occurrence. The decompression grade can be configured depending on the information content of the data and takes into account the measures applied during compression (see description above). Reading individual attribute values from the compressed data proceeds based on the read indicator value. That is, each indicator is 1) NV: attribute value is empty or default value is assigned 2) Vorgaenger: attribute value of the element is equal to the attribute value of the preceding element set in the previous row of the table 3) Index: Index i is read from the compressed data, and the attribute value is equal to the nth element of the table. 4) Explizit: The attribute value is read from the data in an uncompressed state.

The compression algorithm is preferably configured on the client side, for example, so that the client can set the compression type and / or compression grade. This saves data. The following configuration means can be used alone or in any combination. That is, 1) omission of information that cannot be processed on the client side (for example, edge ID, etc.) 2) precision setting unnecessary for applications using decompressed data, for example 3) coordinate precision 4) maximum size of compressed data is set and 5) Maximum x kByte data amount 6) Maximum x m main route length 7) Maximum x min main route travel time, and the like.

The method of the invention can advantageously combine one or more route data or edge data size reduction methods. That is, 1) Coordinate data is reduced by generally limiting the coordinate accuracy (path point resolution). Use relative distances as vectors for previous route points, rather than absolute coordinates as much as possible for one route point.
2) Replace frequently occurring concepts with marks that can be used uniquely (eg, replace “street” with a paragraph symbol). Such concept replacement is predefined without regard to predetermined route data or edge data.
3) Compress the reduced data according to the method of the present invention with yet another common compression algorithm.

  Next, specific examples will be described.

FIG. 4 shows an example of a route graph.
1) The main route goes from point P1 to point P6 via edges K1, K2, and K5. All three edges have the road name “Robert-Bosch Street” and road class 3.
2) Another branch starts from the point P2 via the edges K3 and K4. It belongs to “Hildesheim Street” and has road class 5.

  Indicators that can take the values Explizit, Vorgaenger, Index for the road name for transmission are defined. For the road class, an indicator that can take the values Explizit, Vorgaenger as analog is determined.

  After execution of the compression algorithm, the values for transmission or storage shown in the table below occur. For the sake of clarity, only the edge attribute values to be transmitted or stored are shown here.

It is a flowchart which shows the sequential process of a route graph. FIG. 3 is a block diagram illustrating a compression process using an associative memory. It is a flowchart which shows the compression method of an attribute value. It is a figure which shows the example of a route graph.

Claims (11)

Has various information contents, such as data consisting of topographic nodes and topographic edges and their attribute values,
The compression grade can be configured depending on the information content of the data.
In the data stream data compression method,
A) means for omitting a set attribute value, eg edge ID, for compression;
b) means for limiting the accuracy of topographic information or its coordinates;
c) A method for compressing data in a data stream, characterized in that at least one of means for setting a maximum amount of data and controlling the compression grade accordingly is used.   The method of claim 1, wherein the compression is performed sequentially, i.e., during the compression, the partial data sets are stored sequentially following the first occurrence and transferred to the compressed data area.   For the selected attribute value, for example for transmission, for example whether the corresponding data element exists, or whether a data element is the same as the data element that occurred immediately before, or 3. A method according to claim 1 or 2, wherein an indicator is assigned that indicates whether a data element is the same as a previously transmitted data element.   4. The method according to claim 3, wherein depending on the indicator value, no data element is transmitted, a predetermined data element is transmitted, or an indication for a preceding data element is transmitted following the indicator. Sequentially check nodes to be compressed,
i) compress the attribute value of the current node,
ii) define the current node as the predecessor for the next node;
iii) compress the current edge and its attribute value coming out of the current node;
iv) Define the current edge as the leading edge for the next edge;
v) Check if there is another edge from the current node and compress its attribute value or define it as the second leading edge for the next edge,
5. A method according to any one of claims 1 to 4.   If the predetermined attribute value memory is configured as a buffer memory for compression, one or more indicators are obtained for each data element before moving the data to the compressed data area, and instead of the data value of the data element, 6. A method according to any one of the preceding claims, wherein the method stores and compresses instructions for only one preceding element or for any other data element. Has various information contents, such as data consisting of topographic nodes and topographic edges and their attribute values,
In the data stream decompression method,
Depending on the information content of the data, a) the attribute value set at the time of compression is omitted, for example, means for omitting the edge ID,
b) means for limiting the accuracy of topographic information or its coordinates;
c) A method for decompressing data in a data stream, wherein the decompression grade can be configured in consideration of at least one of means for setting a maximum data amount and controlling the decompression grade accordingly.   8. A method according to claim 7, wherein the decompression is performed sequentially, i.e., during the decompression, partial data sets are sequentially entered into the table following the first occurrence and decompressed.   Assign an indicator to the selected attribute value, and on decompression, whether the data element is empty and possibly assigned a default value, or is a pre-compressed value 9. A method according to claim 7 or 8, wherein it is checked whether or not it is any other known value already assumed.   The method according to claim 1, wherein the compression is performed on a service provider side and the decompression is performed on a user side.   The method according to claim 1, wherein a user, for example, a user of route information in off-board navigation, sets the compression grade or the decompression grade by configuration.

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