DE10221774A1 - Compressing/decompressing data of data stream involves omitting attributes and/or limiting information accuracy and/or specifying maximum data quantity, controlling degree of compression accordingly - Google Patents

Abstract

The method involves configuring the degree of compression in accordance with the information content and using at least one of a set of measures for the compression, i.e. omitting certain attributes, e.g. edge identification, limiting the accuracy of the topographical information, e.g. coordinate accuracy, and specifying a maximum data quantity and controlling the degree of compression accordingly.

Description

State of the art

The invention is based on a method for compressing data Data stream.

DE 101 06 502.7 describes a method for transmitting route data described. The route data include nodes in the form of waypoint data Intermediate edges (paths) and associated attributes. The single ones Waypoints of a route corridor are linked so that one is as possible low data volume is generated. Preferably the waypoint data transmitted sequentially.

DE 101 05 897.7 describes a method for exchanging navigation data between a terminal and a control center described with a segmentation and one Transfer of partial routes between a start and a destination. offboard Navigation devices using this method do not calculate route information autonomously, but request this via a suitable (radio) interface from a server that then transmits it to the navigation device.

DE 100 12 441 C2 describes a method for entering a destination on a navigation device known. To reduce the processing effort, there will only be such Target names included that are in the vicinity of the current location. Moreover the targets are sorted by distance in a target name list.

Advantages of the invention

In the method according to the invention, data of a data stream are different Information content, especially route data from topographic nodes (Waypoints) and edges (connection paths) as well as their attributes (street names, Road classes, etc.), compressed, the degree of compression in Dependency of the information content of the data is configured to be configurable and the compression takes place by omitting predefined attributes the accuracy is limited, e.g. B. in terms of coordinate accuracy, or a maximum amount of data is specified with appropriate control of the Compression degree.

In contrast to known compression methods, in which data regardless of their Meaning or their information content are compressed at the Invention interprets the data and in particular by knowing their meaning redundant elements eliminated.

Optional data fields, for example in a predefined data format Transmission of route information according to DE 101 06 502.7 can be optimal be used.

The method according to the invention is advantageously suitable for the compression of Route data, but can be applied to all possible data, preferably on Data that consists of graphs in their structure, i.e. of polygons topographic nodes and edges, e.g. B. map data, CAD drawings.

The compression method according to the invention is used in particular for offboard Navigation systems preferably used on a server by a service provider, the decompression or decryption of the data preferably on the terminal side or at the client.

• 1. Die Größenreduktion der verarbeiteten Daten, wodurch Übertragungsmedien mit geringen Datenraten gut genutzt werden können.
• 2. Die geringe Komplexität des Komprimierungs- bzw. Dekomprimierungsalgorithmus, so dass sich dieses Verfahren z. B. auch für prozessorschwache Endgeräte mit wenig Arbeitsspeicher eignet.
• 3. Das Komprimierungsverfahren kann streng sequentiell ausgestaltet sein, das heißt bereits während der Komprimierung können Teildatensätze gespeichert bzw. übertragen werden.
• 4. Bei einem sequentiellen Aufbau der komprimierten Daten wird eine Dekomprimierung bereits auf Teildatensätzen noch während der Übertragung ermöglicht.
• 5. Da nicht wie bei vielen anderen Komprimierungsverfahren eine komplette Tabelle mit häufig vorkommenden Datenelementen am Anfang oder am Ende der Daten stehen muss, sondern die einzelnen Elemente an der Stelle eingefügt sind, wo sie erstmalig benötigt werden, ist zu jedem Zeitpunkt der Übertragung eine maximale Anzahl Datenelemente verfügbar.

Advantageous developments of the method according to the invention for compressing or for decompressing are shown in the subclaims. Further advantages of the method can be seen in particular in the following points:

• 1. The size reduction of the processed data, whereby transmission media with low data rates can be used well.
• 2. The low complexity of the compression or decompression algorithm, so that this method z. B. also suitable for low-end devices with little RAM.
• 3. The compression method can be designed to be strictly sequential, which means that partial data records can be stored or transmitted even during the compression.
• 4. With a sequential structure of the compressed data, decompression on partial data sets is made possible even during the transmission.
• 5. Since, as with many other compression methods, a complete table with frequently occurring data elements does not have to be at the beginning or at the end of the data, but the individual elements are inserted at the point where they are needed for the first time, there is a maximum at all times during the transmission Number of data elements available.

drawings

Exemplary embodiments of the invention are explained on the basis of the drawings. It demonstrate

Fig. 1 shows a sequential execution of a route graph

Fig. 2 is a block diagram of a compression process using a content addressable memory,

Fig. 3, the compression of an attribute value,

Fig. 4 shows an example of a route graph.

Description of exemplary embodiments

The method according to the invention assumes that topographical route or Map data consists of waypoints (nodes) and streets (edges), which are as directed connections were created between the nodes. Furthermore, the Nodes and thus the edges of a sequence, which is advantageous for route data from the starting point towards the destination.

• - Koordinaten
• - Eindeutige Kennung (ID)

Waypoints generally have one or more of the following attributes:

• - coordinates
• - Unique identifier (ID)

• - Straßenname
• - Straßenklasse
• - Zielführungsanweisung (grafisch und/oder akustisch)
• - Zielknoten (Verweis auf Wegpunkt)
• - Fahrdauer
• - Weglänge
• - Eindeutige Kennung (ID)

Edges generally have one or more of the following attributes:

• - street name
• - Street class
• - route guidance (graphically and / or acoustically)
• - destination node (reference to waypoint)
• - driving time
• - path length
• - Unique identifier (ID)

• - Datenelement ist nicht vorhanden (bzw. gleich Default-Wert) (N.V.)
• - Datenelement ist gleich dem des Vorgängers (Vorgänger)
• - Datenelement ist gleich dem des x-ten Elements → Index x folgt (Index)
• - Datenwert des Elementes folgt (Explizit).

In the data format used, suitable ones of these attributes are those that are optionally transmitted, e.g. B. IDs or those that have high redundancy, e.g. B. Street names and route guidance instructions each define an indicator that can take two or more of the following values:

• - Data element does not exist (or is the same as the default value) (NV)
• - data element is equal to that of the predecessor (predecessor)
• - data element is equal to that of the xth element → index x follows (index)
• - Data value of the element follows (explicit).

The indicators for each waypoint to be transmitted are advantageously used edge to be transmitted combined into a bit field.

• 1. Übertragen der Punktattribute eines aktuellen Punktes (Ablaufpunkt 3) nach dem Start 1 und der Zuordnung 2 (aktueller Punkt gleich erster Wegepunkt)
• 2. Merken des aktuellen Punktes als Vorgängerpunkt (Ablaufpunkt 4)
• 3. Iterativ über alle vom aktuellen Punkt ausgehenden Kanten, vorzugsweise beginnend bei der Hauptroute (Ablaufpunkt 5)
  • 1. Übertragen der Kantenattribute der aktuellen Kante (Ablaufpunkt 6)
  • 2. Merken der aktuellen Kanten der als Vorgängerkante (Ablaufpunkt 7)
• 4. Vorzugsweise Merken der ersten vom aktuellen Punkt ausgehenden Kante (Hauptroute) als Vorgängerkante (Ablaufpunkt 9).

The compression algorithm now goes through all existing waypoints sequentially and in particular iteratively, cf. Fig. 1:

• 1. Transfer of the point attributes of a current point (sequence point 3 ) after start 1 and assignment 2 (current point equals first waypoint)
• 2. Note the current point as the previous point (process point 4 )
• 3. Iteratively over all edges starting from the current point, preferably starting with the main route (process point 5 )
  • 1. Transfer the edge attributes of the current edge (process point 6 )
  • 2. Note the current edges as the previous edge (process point 7 )
• 4. Preferably note the first edge starting from the current point (main route) as the previous edge (run point 9 ).

At run point 8 , it is examined whether the current point has further edges. If so, the next edge of the current point is selected as the current edge and the process is continued at sequence point 6 .

At process point 10 , it is checked whether there are further points. If this is not the case, the process is ended. Otherwise, the next point is defined as the current point and the process continues again at sequence point 3 .

The actual compression takes place when the attributes are transferred. For this purpose, the compression algorithm has an associative memory 27 ( FIG. 2) for each attribute for which an indicator is defined which can take the value index. The algorithm assigns to each attribute value the number of the element (point / edge) where this value occurs first. So z. B. "Robert-Bosch-Strasse" → 5, which means that the street name "Robert-Bosch-Strasse" appeared first on the 5th edge. The attribute memory 27 is used as a buffer, created during the compression and subsequently deleted again. Alternatively, the element values in the memory can also be assigned to the attribute values. B. 3 if the corresponding attribute value was inserted third in the memory. The compression process 28 is linked directly to the associative memory 27 . The input data is the uncompressed route data and the output data is the compressed route data 30 .

Before the actual point / edge attribute values in the compressed data area the indicator is determined for each element and then instead of the If necessary, only a reference to the previous element or a value Transfer reference to any other element.

The detailed sequence for each individual attribute of a waypoint / edge is described in FIG. 3. According to FIG. 3, it is first checked whether an indicator for an attribute is defined (sequence point 12 ). If yes, it is checked whether the attribute value is filled or valid (process point 13 ). If not, an indicator is defined as NV, i.e. the attribute value remains empty (process point 14 ). Otherwise, it is checked whether the current attribute value is equal to that of the predecessor element (process point 15 ). If this is the case, the attribute value of this element is defined in the same way as the previous element (process point 16 ). Otherwise, it is checked whether an "index" is provided as a permissible value for a current indicator (process point 17 ). If this is the case, it is checked whether the corresponding attribute value is present in the associative memory (process point 18 ). In the positive case, an index is defined for the indicator (process point 19 ). In the negative case, the attribute value or its element number is saved (process point 20 ). The indicator is defined as "explicit", that is, processed uncompressed (process point 21 ). The indicators for the three cases are then written into the memory after the sequence points 21 , 19 and 14 (sequence points 22 , 23 and 24 ) and subsequently the attribute value is written (sequence point 25 ) or the element number (sequence point 26 ).

• - N.V.: Attributwert bleibt leer, bzw. bekommt Defaultwert zugewiesen
• - Vorgänger: Attributwert dieses Elements wird gleich dem des Elements eine Zeile vorher in der Tabelle gesetzt
• - Index: Index i wird aus den komprimierten Daten gelesen und der Attributwert wird gleich dem des n-ten Elementeintrags in der Tabelle gesetzt
• - Explizit: Attributwert wird unkomprimiert aus den Daten gelesen.

When reading in the same order, the decompression goes through the data sequentially, i.e. iteratively over all waypoints and edges, and stores the individual waypoint and edge elements in a table in the order in which they occur. The degree of decompression is configured to be configurable depending on the information content of the data, taking into account the measures taken during the compression (see description there). When reading the individual attribute values from the compressed data, the following is carried out on the basis of the read indicator values:
Indicator is the same

• - NV: Attribute value remains empty or is assigned default value
• - Predecessor: The attribute value of this element is set to that of the element one row before in the table
• - Index: Index i is read from the compressed data and the attribute value is set to that of the nth element entry in the table
• - Explicit: Attribute value is read from the data in an uncompressed state.

• - Weglassen von Informationen, die z. B. (vom Client) nicht verarbeitet werden können, z. B. Kanten IDs
• - Vorgabe von Genauigkeiten, die z. B. für eine Applikation, die die dekomprimierten Daten nutzt, nicht benötigt werden, z. B.:
• - Koordinatengenauigkeit
• - Vorgabe einer maximalen Größe der komprimierten Daten, wodurch der Komprimieralgorithmus die Kompression bei Erreichen des vorgeschriebenen Kriteriums abbricht, z. B.
• - max × kByte Datenmenge
• - max × Meter Länge der Hauptroute
• - max × Minuten Fahrtzeit der Hauptroute
• - . . .

Advantageously, the compression algorithm, e.g. B. be configured by a client, so that (by the client) the type of compression and / or the degree of compression are specified, whereby data can be saved. The following configuration options are possible individually or in combination:

• - omission of information such. B. (cannot be processed by the client), e.g. B. Edge IDs
• - Specification of accuracies z. B. for an application that uses the decompressed data are not required, e.g. B .:
• - coordinate accuracy
• - Specifying a maximum size of the compressed data, whereby the compression algorithm stops the compression when the prescribed criterion is reached, e.g. B.
• - max × kbyte of data
• - Max × length of the main route
• - Max × minutes travel time of the main route
• -. , ,

• - Verringerung der Koordinatendaten dadurch, dass die Koordinatengenauigkeit (Auflösung der Wegepunkte) generell eingeschränkt wird und weiterhin, sofern möglich, für einen Wegpunkt nicht seine absoluten Koordinaten sondern seine relative Entfernung als Vektor zum zuvor übertragenen Wegpunkt übertragen/gespeichert wird
• - Ersetzen von häufig vorkommenden Begriffen durch nicht anderweitig verwendete Sonderzeichen, z. B. "Straße" durch "Paragraphzeichen". Diese Begriffsersetzung ist unabhängig von bestimmten Routen-/Kartendaten und wird vorab definiert
• - Weiteres Komprimieren der nach diesem Verfahren reduzierten Daten durch einen anderen allgemeinen Komprimierungsalgorithmus

The method according to the invention can advantageously be combined in one or more of the following methods for reducing the size of the route / map data:

• - Reduction of the coordinate data by generally restricting the coordinate accuracy (resolution of the waypoints) and, if possible, for a waypoint not its absolute coordinates but rather its relative distance is transmitted / saved as a vector to the previously transmitted waypoint
• - Replace frequently occurring terms with special characters not used elsewhere, e.g. B. "Street" by "paragraph sign". This term replacement is independent of certain route / map data and is defined in advance
• - Further compression of the data reduced according to this method by another general compression algorithm

A concrete exemplary embodiment is described below.

• - Die Hauptroute verläuft vom Punkt P1 über die Kanten K1, K2 und K5 zu Punkt P6. Alle drei Kanten haben den Straßennamen "Robert-Bosch-Straße" und die Straßenklasse 3.
• - An Punkt P2 beginnt ein Abzweig über die Kanten K3, K4, die zur Hildesheimer Straße gehören und der Straßenklasse 5 zugeordnet sind.

A route graph is shown as an example in FIG. 4:

• - The main route runs from point P1 over edges K1, K2 and K5 to point P6. All three edges have the street name "Robert-Bosch-Straße" and the street class 3.
• - At point P2, a branch begins via edges K3, K4, which belong to Hildesheimer Straße and are assigned to street class 5.

For the transmission, an indicator is agreed for the street names, the values Can explicitly assume predecessor and index. Analogously for the street class Indicator with the possible values explicit and predecessor.

After running through the compression algorithm, the values for transmission / storage shown in the following table result. For the sake of simplicity, only the attributes of the edges to be transferred / stored are shown here.

Claims (11)

1. Method for compressing data of a data stream of different information content, in particular data consisting of topographic nodes and edges and their attributes, the degree of compression being configurable depending on the information content of the data and at least one of the following measures being used for compression: - omitting predefined attributes, e.g. B. edge identifications, - Limiting the accuracy of the topographic information, e.g. B. their coordinate accuracy, - Specification of a maximum amount of data and corresponding control of the degree of compression. 2. The method according to claim 1, characterized in that the compression is carried out sequentially, i.e. during the compression of partial data records stored in the order of their first appearance and in the compressed data area are transmitted. 3. The method according to claim 1 or 2, characterized in that selected Attributes, especially for the transmission, an indicator is assigned to Identification of whether there is a data element in particular, whether that Data element is equal to the immediately preceding data element or whether that Data element is equal to a previously transmitted data element. 4. The method according to claim 3, characterized in that depending on the Indicator value is not a data element, a data element or a reference to one earlier data element is transmitted following the indicator. 5. The method according to any one of claims 1 to 4, characterized in that for compression existing nodes are checked sequentially to - compress the attributes of the current node, - define a current node as a predecessor node for a subsequent node, - compress the current edge starting from a current node and its attributes, - to define the current edge as the previous edge for a subsequent edge, - to check whether further edges originate from a current node and to compress their attributes or to define them as another predecessor edge for a further subsequent edge. 6. The method according to any one of claims 1 to 5, characterized in that for the Compression of an attribute store is provided as a cache to before the transfer of the data into the compressed data area for a data element to determine the indicator, so instead of the data value of the data element possibly only a reference to a predecessor element or a reference to any other data element must be saved or compressed. 7. Method for decompressing data of a data stream with different information content, in particular data consisting of topographic nodes and edges and their attributes, the degree of decompression being configured to be configurable depending on the information content of the data, taking into account measures taken during the compression, such as: - omitting predefined attributes, e.g. B. edge identifications, - Limiting the accuracy of the topographic information, e.g. B. the coordinate accuracy, - Specifying a maximum amount of data and corresponding control of the degree of decompression. 8. The method according to claim 7, characterized in that the decompression is carried out sequentially, i.e. during decompression Partial data records in the order in which they first appear in a table entered and then decompressed. 9. The method according to any one of claims 7 or 8, characterized in that selected attributes, to which indicators are assigned, during decompression thereupon it is examined whether data elements are empty and, if applicable, them a default value can be assigned, it is an already compressed one Predecessor value or any other already known value, the can be taken over. 10. The method according to any one of claims 1 to 6 and one of claims 7 to 9, characterized in that the compression at a service provider and the Decompression is done at a service user. 11. The method according to any one of claims 1 to 10, characterized in that the Degree of compression or decompression by a service user, e.g. B. the Users of route information in offboard navigation through configuration is specified.