CN102298640B - Method for preprocessing map display data - Google Patents

Abstract

The invention relates to a method for preprocessing map display data, which is characterized in that it includes three parts: 1) establishing a multi-resolution secondary grid index storage structure, and realizing an estimated reading strategy based on the index storage structure; 2) The display object density of each grid is individually controlled, so as to select a reasonable display object; 3) Combining with the resolution of human eyes, the display objects in each grid are simplified. The present invention can obtain higher loading efficiency in map directional mobile display, ensure that the display content density in each scale and each area is more reasonable, and simplify the display object under the premise of ensuring the human visual effect, reducing the to display the amount of data. The invention can be widely applied in various vehicle navigation systems, and realizes high-efficiency loading of map display data.

Description

A method of map display data preprocessing

technical field

The invention relates to a data preprocessing method, in particular to a map display data preprocessing method in a car navigation system.

Background technique

One of the main functions of the vehicle autonomous navigation system is to display the electronic map in real time and provide relevant navigation information. At present, with the continuous development of geographic information systems, the amount of data required to display electronic maps is also expanding. Most of the vehicle-mounted autonomous navigation systems are built on the hardware platform based on embedded devices, and the computing power of the processor and the speed of file reading and writing are greatly limited. If these image data are not pre-organized and processed, there may be Unreasonable display content occurs, such as too few, stacked or overlapping phenomena, and sometimes it is even difficult to realize the real-time display of the electronic map. To solve this problem, the image data to be displayed in the electronic map is usually preprocessed. The existing processing methods mainly include: 1. Establish a multi-level grid index or tree structure, combined with a cache mechanism, to realize fast positioning and loading of data. The disadvantage is that the cache mechanism is more suitable for the situation where the map moves randomly. The directional movement display commonly used in navigation has poor adaptability; 2. Use the administrative level of the display object to specify the display level for it, and display objects of a specific level under each scale to select the display content of each scale. The disadvantages are: In different areas of the same scale, the display density may vary greatly, sometimes it may be too dense, sometimes it may be too thin, and the amount of information provided to the user is too small; 3. The geometric properties (usually curves) of the displayed object Appropriate compression and simplification achieve the purpose of simplifying the display content. The disadvantages are: the similarity of the display objects in all directions is not fully utilized, the compression rate is not high, and the error parameters used in compression are not as resolvable as human eyes. Combined, there may be overcompression (degraded display) or undercompression (lower compression ratio).

Contents of the invention

At the problems referred to above, the object of the present invention is to provide a method for preprocessing map display data in a vehicle navigation system, which can 1, establish a reasonable map grid organization and indexing method, and take into account the commonly used orientation in navigation Mobile display needs, combined with the estimated loading strategy to achieve fast positioning and loading of data, better loading efficiency can be obtained in directional mobile display; 2. Control the grid grid size of the map, and adjust the display object density of each grid Independent control to ensure that the density of displayed content in each scale and area is relatively reasonable, and provide users with reasonable geographic information; 3. Combined with the resolution of the human eye, the display objects in each grid are simplified to avoid excessive Compression or undercompression.

In order to achieve the above object, the present invention adopts the following technical solutions: a method for preprocessing map display data, which includes three parts: establishing a grid index storage structure, selecting display objects for each grid, and simplifying display objects;

1) Establish a grid index storage structure, including the following steps:

① Divide the map under each level of scale into two layers of grids: the bottom grid and the top grid, the size of the bottom grid is equal to the size of the screen, and each top grid includes several bottom grids;

② Establish a grid index for the top-level grid obtained by step ① division;

③For the four vertices of the current screen, determine the top-level grid where they are located according to the grid index established in step ②, and further determine the underlying grid where they are located in the top-level grid;

④ Store the data contained in several underlying grids in the cache, and set a abandonment index for each underlying grid at the same time. The abandonment index is a variable whose size is the distance between the center point of the underlying grid and the center point of the screen, and Empty cache cells also have a abandonment index set to a positive value greater than the abandonment index of all other underlying grids;

⑤ Every time the screen is refreshed, the system updates and records the abandonment index of all underlying grids in the current cache:

If the system issues an instruction to load more than one underlying grid into the cache, perform step ⑥;

If the system does not issue an instruction to load the underlying grid into the cache, perform step ⑦;

⑥i) Load an underlying grid and search the cache again:

If the underlying grid to be loaded already exists in the cache, directly extract the underlying grid data;

If the underlying grid to be loaded is not stored in the cache, read the underlying grid data from the file, put it into the cache, and replace the underlying grid with the largest abandonment index in the current cache;

ii) return to step i), and load another underlying grid until all the underlying grids that need to be loaded are loaded;

⑦i) each bottom grid in the current cache is searched for its adjacent bottom grid, that is, searching for an adjacent grid with a coincident edge with the bottom grid, and recording the corresponding abandonment index;

ii) Select the bottom grid with the smallest abandonment index from the adjacent bottom-level grids obtained in step i), load its data into the cache, and replace the bottom-level grid with the largest abandonment index marked in step 5;

2) Select display objects for each grid, including the following steps:

①Set a reasonable range of curve density for all underlying grids;

② Mark the display level of the display object;

③ For an underlying grid, start from the highest level in the display hierarchy, and fill the underlying grid with display objects step by step from high to low:

If after completing one level of filling, the curve density of the underlying grid just enters the reasonable range of curve density given by step ①, stop filling the underlying grid, return to step ③, and fill another underlying grid , until all underlying grids are filled;

If after completing a level of filling, the curve density of the underlying grid is greater than the maximum value of the reasonable range of the curve density given by step ①, then abandon this level of filling, and keep the filling result of the previous level as the final result, and return Step ③, filling another underlying grid until all underlying grids are filled;

If after one level of filling is completed, the curve density of the underlying grid is still less than the minimum value of the reasonable range of curve density given in step ①, then continue to fill the underlying grid with a lower level;

3) Refine display objects for each grid, including the following steps:

① Use the direction priority method to splice the end-to-end road sections in the underlying grid, that is, when the two road sections are connected end-to-end, and the acute angle formed at the connection is less than a given angle threshold, the two road sections are spliced;

② Use the node invariance method to simplify the original polyline in the display result obtained in step ①, and reduce the redundant shape value points of the road section. The specific steps are as follows:

i) find out the nodes at all splicing places from the original polyline, and record the node positions;

ii) Douglas-Peucker thinning simplification is performed on the original polyline, and all sub-sections in the polyline whose chord height is less than a given chord height threshold are simplified to straight line segments;

iii) inserting all nodes into corresponding positions according to the node positions recorded in step i);

③ Use the dynamic threshold method to merge road sections with similar normal distances:

Designate the road section set before merging as F={F _i }, the road section set after merging as G={G _k }, the initial state of the road section set after merging is an empty set, and the road section to be merged in the road section set F before merging is F _i , P _i is a shape point on F _i , the new branch road section is U, and the point closest to P _i in the merged road section set G is L _i ; if the distance between P _i and L _i is less than the value of the current dynamic distance threshold , the difference between the tangent angles of the two points is less than the value of the current dynamic angle threshold, and the two points can be merged. The merge process is as follows:

i) Find a road section F _i to be merged from the road section set F before merging;

ii) Find a shape point P _i from the road section F _i to be merged;

iii) Find the point L _i closest to the shape point P _i in the merged road section set G:

If P _i and L _i are merged successfully, add point P _i at the end of the new branch road section U, and add this road section U to the merged road section set G, and then clear the new branch road section U;

If the combination of P _i and L _i fails, only add point P _i at the end of the new branch road section U;

iv) Return to step ii), find another shape point P _i+1 from the road section F _i to be merged, until all shape points on the road section F _i to be merged are processed;

v) Return to step i), find another road segment F _i+1 to be merged from the road segment set F before merging, until all road segments in the road segment set F to be merged are processed, and end.

In step ① of the above part 2), the reasonable range of the curve density refers to the number of curves in the interval [50, 150] in an underlying grid.

In step ② of the above part 2), the display level is marked according to the administrative level of the display object.

In step ① of the above part 3), the angle threshold is 30°.

In the step ② of the above part 3), according to the limit resolution of 1.5' of human vision under the conditions of medium brightness and medium contrast, the resolution limit distance of the human eye on the screen is converted, and the current screen resolution limit distance is converted to is the corresponding geographic scale distance, as the chord height threshold.

In step ③ of the above-mentioned part 3), the setting method of the dynamic distance threshold and the dynamic angle threshold is:

When the previous point is merged successfully, the values of the dynamic distance threshold and the dynamic angle threshold used for the current judgment are respectively 110% of the reference distance threshold and the reference angle threshold;

When the combination at the previous point fails, the values of the dynamic distance threshold and the dynamic angle threshold used for the current judgment are respectively 90% of the reference distance threshold and the reference angle threshold.

The aforementioned reference angle threshold is 30°.

The present invention has the following advantages due to the adoption of the above technical solutions: 1. Because the positioning of the secondary grid index storage structure constructed by the present invention is fast and simple, its cache strategy fully takes into account the directional movement conditions that often occur in the navigation process, When there is no loading task, the grid with the smallest estimated abandonment index is properly loaded, thus reducing the need to load the underlying grid once during directional movement, thereby reducing the peak time consumption of data loading. 2. Since the present invention controls the display object density independently for each grid of each scale, it can ensure that the display content density in each scale and each area is relatively reasonable, avoiding the occurrence of local over-density or over-sparse problems, thereby providing Users provide reasonable geographic information display. 3. Since the present invention determines the simplification parameters of the display objects in combination with the resolution of the human eye, and simplifies the display objects in each grid, the occurrence of over-compression or under-compression is avoided, and the processing burden of the display engine is reduced. The invention can be widely applied in various vehicle navigation systems, and realizes high-efficiency loading of map display data.

Description of drawings

Fig. 1 is a work flow chart of the present invention

Fig. 2 is a schematic diagram of the data storage structure of the present invention

Fig. 3 is a schematic diagram of indexing and sorting of the top-level grid of the present invention

Fig. 4 is a schematic diagram of cache loading in the present invention

Fig. 5 is a simplified schematic diagram of nodes invariant in the present invention

Fig. 6 is a schematic diagram of curve merging in the present invention

Detailed ways

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

As shown in Fig. 1 and Fig. 2, the present invention all comprises the following steps to the preprocessing of each level of scale map data:

1) Establish grid index storage structure;

2) Select display objects for each grid;

3) Thin display objects for each grid.

After the above three steps are completed, the data of each grid can be stored as a file according to the grid index storage structure established in step 1), and then a multi-resolution map display database can be established.

The specific implementation method of the above steps is described as follows:

1) Establishing a grid index storage structure is to divide the map into grids, establish a secondary grid index storage structure, and combine the estimated loading strategy to realize fast positioning and fast loading of data, which includes the following steps:

① Divide the map at each level of scale into two layers of grids: the bottom grid and the top grid, where the size of each bottom grid is equal to the size of the screen, and each top grid includes four bottom grids , can also include six, the number is not limited to this.

②As shown in Figure 3, for the top-level grid obtained by step ①, establish a grid index according to the existing technical scheme: that is, assign a grid number to all the top-level grids in order of their longitude and latitude from small to large , so as to establish a one-to-one correspondence relationship between the grid number and the latitude and longitude interval. Therefore, by giving the latitude and longitude value of the geographic coordinate point, the top-level grid where it is located can be quickly located to avoid redundant data reading. Among them, if the given geographical coordinate point is exactly on the common side of the two top-level grids, move the point to the center of the screen for a unit distance e along the direction of the line connecting it with the center point of the screen to obtain a new point, Makes the top-level grid where this point is located as the top-level grid where the point with the given geographic coordinates is located.

③For the four vertices of the current screen, determine the top-level grid where they are located according to the grid index established in step ②, and further determine the underlying grid where they are located in the top-level grid through their respective geographic coordinates of latitude and longitude; the current screen The four bottom-level grids where the four vertices are located contain the display data needed for the current screen display.

④Establish a grid cache: store the data contained in several underlying grids in the cache, and set a abandonment index for each underlying grid at the same time. The abandonment index is a variable whose size is the center point of the underlying grid and the screen The distance between the center points. Among them, the underlying grid data with the largest abandonment index will be cleared out of the cache by the cache management system first. And the cache unit that is empty also sets a abandonment index, and its size is set to a positive value greater than the abandonment index of all other underlying grids, such as 100000.

⑤As shown in Figure 4, every time the screen is refreshed, the system updates and records the abandonment index of all underlying grids in the current cache:

If the system issues an instruction to load more than one underlying grid into the cache, perform step ⑥;

If the system does not issue an instruction to load the underlying grid into the cache, go to step ⑦.

⑥i) Load an underlying grid and search the cache again:

If the underlying grid to be loaded already exists in the cache, directly extract the underlying grid data;

If there is no underlying grid to be loaded in the cache, read the underlying grid data from the file, put it into the cache, and replace the underlying grid with the largest abandonment index in the current cache.

ii) Return to step i), and load another underlying grid until all the underlying grids that need to be loaded are loaded.

⑦i) For each underlying grid in the current cache, search its adjacent underlying grid, that is, search for an adjacent grid that has a coincident edge with the underlying grid, and record the corresponding abandonment index.

ii) Select the underlying grid with the smallest abandonment index from the adjacent underlying grids obtained in step i), load its data into the cache, and replace the underlying grid with the largest abandonment index marked in step ⑤.

2) Selecting display objects for each grid is to select and display road section objects for the underlying grids under each scale within a reasonable range of given curve density, which includes the following steps:

①Set a reasonable range of curve density for all underlying grids;

The reasonable range of curve density means that in an underlying grid, the number of curves is in the interval [50, 150], and this interval is usually determined by practical experience.

② According to the administrative level of the display object, mark the display level. For example, the national highway is the highest level road section display object, and it can also be classified according to other properties of the display object, not limited to this.

③ For an underlying grid, start from the highest level in the display hierarchy, and fill the underlying grid with display objects step by step from high to low:

If after completing one level of filling, the curve density of the underlying grid just enters the reasonable range of curve density given by step ①, stop filling the underlying grid, return to step ③, and fill another underlying grid , until all underlying grids are filled;

If after completing a level of filling, the curve density of the underlying grid is greater than the maximum value of the reasonable range of the curve density given by step ①, then abandon this level of filling, and keep the filling result of the previous level as the final result, and return Step ③, filling another underlying grid until all underlying grids are filled;

If after one level of filling is completed, the curve density of the underlying grid is still less than the minimum value of the reasonable range of the curve density given by step ①, continue to fill the underlying grid with a lower level.

3) Simplifying the display objects for each grid is to determine the simplified parameters of the display objects in combination with the resolution of the human eye, and simplify the display objects in each underlying grid to achieve the purpose of reducing the number of road sections and compressing the amount of data, which includes the following steps :

① Use the direction priority method to splice the end-to-end road sections in the underlying grid to reduce the number of displayed road sections:

It is stipulated that when two road sections are connected end to end, and the acute angle formed at the connection is smaller than a given angle threshold, the two road sections are spliced. The angle threshold can be set to 30°, based on the following: when the angle threshold is set too large, the shape of the spliced curve will be too complex, which is not conducive to drawing; when the angle threshold is set too small, it will reduce The beneficial effect of the number of road segments; experiments show that: setting the angle threshold to 30° can achieve a better balance between the two.

Specify the original set of road sections as E={E _i }, the set of road sections to be expanded as D={D _k }, the initial state of the set of road sections to be expanded is an empty set, and i and k are element subscripts.

Perform a round of loose splicing: first extract a road segment E _i from the original road segment set E, if there is a road segment D _k that can be spliced with E _i in the road segment set D to be expanded, then put E _i and D _k into D Otherwise, directly put E _i into D, and then extract another road segment E _i+1 from the original road segment set E to continue splicing until all the road segments in E are taken out.

After one round of relaxed splicing is performed, the obtained road segment set D to be expanded is used as the original road segment set E for the next round of relaxed splicing, and the next round of relaxed splicing is started until there is no road segment that can be spliced.

② Use the node invariant method to simplify the original polyline in the display result obtained in step ①, so as to reduce the redundant shape value points of the road section and reduce unnecessary resolution. It should be noted that if the nodes at the original polyline joint are deleted by the simplification algorithm, the joint may be discontinuous with other road sections, which will affect the appearance. Therefore, the nodes need to be replaced after the simplification is completed. As shown in Figure 5, the specific steps are as follows:

i) Find all spliced nodes from the original polyline, and record the node positions.

ii) Perform Douglas-Peucker thinning and simplification on the original polyline. In this process, a chord height threshold is set, and all sub-sections in the polyline whose chord height is less than the given chord height threshold are simplified to straight line segments; the setting of the chord height threshold The method is as follows: under the conditions of medium brightness and medium contrast, the limit resolution of human vision is 1.5', from this, the resolution limit distance of the human eye on the screen is converted, and the current screen resolution limit distance is converted into the corresponding The geographical scale distance can be used as the chord height threshold.

iii) According to the node positions recorded in step i), insert all the nodes back to the corresponding positions.

③ As shown in Figure 6, the dynamic threshold method is used to merge road sections with similar normal distances to further reduce the number of road sections:

Designate the road section set before merging as F={F _i }, the road section set after merging as G={G _k }, the initial state of the road section set after merging is an empty set, and the road section to be merged in the road section set F before merging is F _i , P _i is a shape point on F _i , the new branch road section is U, and the point closest to P _i in the merged road section set G is L _i ; if the distance between P _i and L _i is less than the value of the current dynamic distance threshold , the difference between the tangent angles of the two points is less than the value of the current dynamic angle threshold, and the two points can be merged. The specific process of merging is as follows:

i) Find a road section F _i to be merged from the road section set F before merging;

ii) Find a shape point P _i from the road section F _i to be merged;

iii) Find the point L _i closest to the shape point P _i in the merged road section set G:

If P _i and L _i are merged successfully, add point P _i at the end of the new branch road section U, and add this road section U to the merged road section set G, and then clear the new branch road section U;

If the combination of P _i and L _i fails, only add point P _i at the end of the new branch road section U;

iv) Return to step ii), find another shape point P _i+1 from the road section F _i to be merged, until all shape points on the road section F _i to be merged are processed;

v) Return to step i), find another road segment F _i+1 to be merged from the road segment set F before merging, until all road segments in the road segment set F to be merged are processed, and end.

Among them, the setting method of dynamic distance threshold and dynamic angle threshold is as follows:

When the previous point is merged successfully, the distance threshold and angle threshold used for the current judgment are respectively 110% of the reference distance threshold and the reference angle threshold;

When the combination at the previous point fails, the distance threshold and the angle threshold used for the current judgment take 90% of the reference distance threshold and the reference angle threshold respectively.

The determination method of the reference distance threshold is the same as that of the chord height threshold in step ②; the reference angle threshold can be set to 30° based on experimental experience.

Claims (12)

1. A method for preprocessing map display data, which includes three parts: establishing a grid index storage structure, selecting display objects and simplifying display objects for each grid; 1) Establish a grid index storage structure, including the following steps: ① Divide the map under each level of scale into two layers of grids: the bottom grid and the top grid, the size of the bottom grid is equal to the size of the screen, and each top grid includes several bottom grids; ② Establish a grid index for the top-level grid obtained by step ① division; ③For the four vertices of the current screen, determine the top-level grid where they are located according to the grid index established in step ②, and further determine the underlying grid where they are located in the top-level grid; ④ Store the data contained in several underlying grids in the cache, and set a abandonment index for each underlying grid at the same time. The abandonment index is a variable whose size is the distance between the center point of the underlying grid and the center point of the screen, and Empty cache cells also have a abandonment index set to a positive value greater than the abandonment index of all other underlying grids; ⑤ Every time the screen is refreshed, the system updates and records the abandonment index of all underlying grids in the current cache: If the system issues an instruction to load more than one underlying grid into the cache, perform step ⑥; If the system does not issue an instruction to load the underlying grid into the cache, perform step ⑦; ⑥i) Load an underlying grid and search the cache again: If the underlying grid to be loaded already exists in the cache, directly extract the underlying grid data; If the underlying grid to be loaded is not stored in the cache, read the underlying grid data from the file, put it into the cache, and replace the underlying grid with the largest abandonment index in the current cache; ii) return to step i), and load another underlying grid until all the underlying grids that need to be loaded are loaded; ⑦i) each bottom grid in the current cache is searched for its adjacent bottom grid, that is, searching for an adjacent grid with a coincident edge with the bottom grid, and recording the corresponding abandonment index; ii) Select the bottom grid with the smallest abandonment index from the adjacent bottom-level grids obtained in step i), load its data into the cache, and replace the bottom-level grid with the largest abandonment index marked in step 5; 2) Select display objects for each grid, including the following steps: ①Set a reasonable range of curve density for all underlying grids; ② Mark the display level of the display object; ③ For an underlying grid, start from the highest level in the display hierarchy, and fill the underlying grid with display objects step by step from high to low: If after completing one level of filling, the curve density of the underlying grid just enters the reasonable range of curve density given by step ①, stop filling the underlying grid, return to step ③, and fill another underlying grid , until all underlying grids are filled; If after completing a level of filling, the curve density of the underlying grid is greater than the maximum value of the reasonable range of the curve density given by step ①, then abandon this level of filling, and keep the filling result of the previous level as the final result, and return Step ③, filling another underlying grid until all underlying grids are filled; If after one level of filling is completed, the curve density of the underlying grid is still less than the minimum value of the reasonable range of curve density given in step ①, then continue to fill the underlying grid with a lower level; 3) Refine display objects for each grid, including the following steps: ① Use the direction priority method to splice the end-to-end road sections in the underlying grid, that is, when the two road sections are connected end-to-end, and the acute angle formed at the connection is less than a given angle threshold, the two road sections are spliced; ② Use the node invariance method to simplify the original polyline in the display result obtained in step ①, and reduce the redundant shape value points of the road section. The specific steps are as follows: i) find out the nodes at all splicing places from the original polyline, and record the node positions; ii) Douglas-Peucker thinning simplification is performed on the original polyline, and all sub-sections in the polyline whose chord height is less than a given chord height threshold are simplified to straight line segments; iii) inserting all nodes into corresponding positions according to the node positions recorded in step i); ③ Use the dynamic threshold method to merge road sections with similar normal distances: Designate the road section set before merging as F={F _i }, the road section set after merging as G={G _k }, the initial state of the road section set after merging is an empty set, and the road section to be merged in the road section set F before merging is F _i , P _i is a shape point on F _i , the new branch road section is U, and the point closest to P _i in the merged road section set G is L _i ; if the distance between P _i and L _i is less than the value of the current dynamic distance threshold , the difference between the tangent angles of the two points is less than the value of the current dynamic angle threshold, the two points can be merged, and the merge process is as follows: i) Find a road section F _i to be merged from the road section set F before merging; ii) Find a shape point P _i from the road section F _i to be merged; iii) Find the point L _i closest to the shape point P _i in the merged road section set G: If P _i and L _i are merged successfully, add point P _i at the end of the new branch road section U, and add this road section U to the merged road section set G, and then clear the new branch road section U; If the combination of P _i and L _i fails, only add point P _i at the end of the new branch road section U; iv) Return to step ii), find another shape point P _i+1 from the road section F _i to be merged, until all shape points on the road section F _i to be merged are processed; v) Return to step i), find another road segment F _i+1 to be merged from the road segment set F before merging, until all road segments in the road segment set F to be merged are processed, and end. 2. A kind of map display data preprocessing method as claimed in claim 1, it is characterized in that: in the step 1. of said part 2), the reasonable range of said curve density refers to that in a bottom grid, the number of curves is [50, 150] interval. 3. A method for preprocessing map display data according to claim 1, characterized in that: in step ② of said part 2), the display level is marked according to the administrative level of the display object. 4. A method for preprocessing map display data according to claim 2, characterized in that: in step ② of said part 2), the display level is marked according to the administrative level of the display object. 5. A method for preprocessing map display data according to claim 1 or 2 or 3 or 4, characterized in that: in step ① of said part 3), said angle threshold is 30°. 6. A kind of map display data preprocessing method as claimed in claim 1 or 2 or 3 or 4, it is characterized in that: in the step ② of said part 3), according to human vision in medium brightness, under the condition of medium contrast The limit resolution of the screen is 1.5', and the resolution limit distance of the human eye on the screen is converted, and the current screen resolution limit distance is converted into the corresponding geographical scale distance by using scale transformation, which is used as the chord height threshold. 7. A kind of map display data preprocessing method as claimed in claim 5, it is characterized in that: in the step ② of described part 3), according to the limit resolution 1.5' under the conditions of medium brightness and medium contrast of human vision , convert the resolution limit distance of the human eye on the screen, and convert the current screen resolution limit distance into a corresponding geographical scale distance by using scale transformation, which is used as the chord height threshold. 8. A method for preprocessing map display data as claimed in claim 1 or 2 or 3 or 4 or 7, characterized in that: in step ③ of said part 3), said dynamic distance threshold and said dynamic angle The method of setting the threshold is: When the previous point is merged successfully, the values of the dynamic distance threshold and the dynamic angle threshold used for the current judgment are respectively 110% of the reference distance threshold and the reference angle threshold; When the combination at the previous point fails, the values of the dynamic distance threshold and the dynamic angle threshold used for the current judgment are respectively 90% of the reference distance threshold and the reference angle threshold. 9. A kind of map display data preprocessing method as claimed in claim 5, is characterized in that: in the step 3. of said part 3), the setting method of said dynamic distance threshold and said dynamic angle threshold is: When the previous point is merged successfully, the values of the dynamic distance threshold and the dynamic angle threshold used for the current judgment are respectively 110% of the reference distance threshold and the reference angle threshold; When the combination at the previous point fails, the values of the dynamic distance threshold and the dynamic angle threshold used for the current judgment are respectively 90% of the reference distance threshold and the reference angle threshold. 10. A kind of map display data preprocessing method as claimed in claim 6, is characterized in that: in the step 3. of said part 3), the setting method of said dynamic distance threshold and said dynamic angle threshold is: When the previous point is merged successfully, the values of the dynamic distance threshold and the dynamic angle threshold used for the current judgment are respectively 110% of the reference distance threshold and the reference angle threshold; When the combination at the previous point fails, the values of the dynamic distance threshold and the dynamic angle threshold used for the current judgment are respectively 90% of the reference distance threshold and the reference angle threshold. 11. A method for preprocessing map display data according to claim 8, characterized in that: the reference angle threshold is 30°. 12. A method for preprocessing map display data according to claim 9 or 10, characterized in that: the reference angle threshold is 30°.

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