Processing method for lightening geographic information vector data file

Abstract

The invention relates to the field of engineering survey design, and particularly discloses a geographic information vector data file lightweight processing method, which comprises the following steps of: dividing geographic information vector data into three categories of point elements, line elements and surface elements, simplifying the attribute expression of each category of elements, and grouping; deleting redundant points to simplify geometric composition of the line elements and the surface elements, and performing preliminary simplification on the file; reordering the point elements according to the length of the geometric distance of the point elements as an ordering rule; calculating geometric difference values of the elements, and replacing the original geometric coordinates with the difference values; and converting the difference value into an integer to delete a null value to further simplify the file so as to complete file weight reduction. According to the method, the geographic information vector data file element forming mode is comprehensively considered, on the basis of ensuring the annotation information, the precision and the topological structure of the original geographic information file, redundant points are rapidly deleted, the complexity of element expression is simplified, and the size of the geographic information vector data file is remarkably reduced.

Description

Technical Field

[0001] The invention relates to the field of engineering survey and design, and in particular to a lightweight processing method for geographic information vector data files. Background Art

[0002] Geographic information vector data files are an inaccessible part of the engineering survey and design process and are an intuitive way to show production results. With the continuous development of digital technology, engineering survey work has gradually upgraded the traditional stand-alone application environment to the network application environment. Therefore, data storage and transmission are particularly important. Data files produced in traditional stand-alone environments, such as dwg, dxf and other files, need to be reconstructed into data formats that can be used by network platforms, such as geojson, kml, shp and other files. Due to the shortcomings of computer automatic reconstruction of files in simplification, the information content cannot be recognized during the conversion process. In the process of preparing geographic information vector data, if the set accuracy is too large, the density of collected points is large, resulting in the amount of information in the generated data file being too redundant and wasteful; on the contrary, if the interval between the collected points is small, the accuracy of the generated data file cannot be met. In order to ensure the accuracy of geographic information description, the collection of geographic information points is generally conservative, so the generated data files will occupy a relatively large amount of memory. On this basis, directly using the reconstructed data files will affect the application effect in the network application environment. On the one hand, large-volume data files not only increase the waiting time for file transmission, but also increase the safety risks during file transmission. On the other hand, redundant data information will increase the difficulty of file processing and require more manpower and time to maintain. Summary of the invention

[0003] In order to meet the needs of engineering survey and design professionals to use geographic information vector data files on the network platform, the difficulty of processing geographic information vector data in map making is simplified. The purpose of the present invention is to provide a lightweight processing method for geographic information vector data files, which improves the processing efficiency of geographic information vector data and reduces the map data storage memory while ensuring the accuracy requirements of the data files.

[0004] To achieve the above object, the technical solution proposed by the present invention is: a method for lightweight processing of geographic information vector data files, comprising the following steps:

[0005] S1: Divide geographic information vector data into three categories: point features, line features and surface features, simplify the attribute expression of each category of features and group them;

[0006] S2: Delete the redundant geometric points of line elements and surface elements under the condition of meeting the allowable error, so as to achieve the initial simplification of the file;

[0007] S3: Re-sort the point features according to their geometric distance.

[0008] S4: Calculate the difference between the coordinate values ​​of adjacent points in the geometric information of the point feature set, line feature, and surface feature, and replace the original geometric information expression with the difference;

[0009] S5: Convert the geometric coordinates of the features into integers and remove null values ​​to further simplify the file, thereby achieving lightweight geographic information vector data files.

[0010] Optionally, simplifying the attribute expression of each category of elements and grouping them includes: merging elements with the same reference attribute value to reconstruct a new point element set F p , line feature set F l , polygon feature set F A , and thereby establish the attribute table Q.

[0011] Furthermore, the reference attributes of the point elements, line elements, and surface elements are freely selected, and the default is all the attributes of the entire layer.

[0012] Optionally, deleting redundant geometric points of line elements and surface elements under the condition of satisfying an allowable error includes:

[0013] S21: Set line feature set F l and the polygon feature set F A Simplified tolerance value t;

[0014] S22: Use the Douglas-Peucker algorithm to delete the line feature set F within the allowable error value t l and the polygon feature set F A Redundant geometric coordinate points in the generated simplified line feature set F l ′ and the face element set F A ′.

[0015] Furthermore, the process of deleting redundant points in element geometric information using the Douglas-Peucker algorithm includes:

[0016] S221: Remove the polygon element F A The end point in the geometry information that coincides with the start point, line feature F l The geometric information remains unchanged as the feature to be processed F d ;

[0017] S222: Element F d The geometric information W is composed of points P|(x, y)∈R, and an empty set W′ is created as the new geometric information;

[0018] S223: Element F dThe starting and ending points of are added to the set W′:

[0019] S224: Connect the coordinate points in the set W to generate a reference line set L;

[0020] S225: Calculate W at the endpoint P of the reference line l∈L s (x s ,y s ), P e (x e ,y e ) The distance D between the point P′(x′,y′) in the middle range and l, and the maximum distance is recorded as D max , and the corresponding point is P m ' ax , where the distance D is calculated as follows:

[0021]

[0022] S226: Compare the maximum distance D max With the allowable error value t: If D max ≤t, then delete all P′; if D max >t, then P m ' ax Insert into the set W′ and repeat steps S224 to S226;

[0023] S227: Redundant points are deleted and W′ is used as the element F d New geometry information.

[0024] Furthermore, the new line element F in step S227 l ′ and the new face element F A 'Processing includes:

[0025] Line features are directly equivalent to F d ;

[0026] Area elements need to be F d Perform closing processing, including: copy F d The starting point of the geometric information W′ is inserted to the end as the end point, and the final line element geometric information W l ′ and the geometric information W of the surface element A The expression of ′ is as follows:

[0027]

[0028] Optionally, the step of reordering the point elements according to the geometric distance of the point elements as a sorting rule includes:

[0029] S31: Select a point element located at an edge corner position in the point element set as the starting point C(x, y), and place it in the new point element set U;

[0030] S32: Calculate the distance S between C and other points, find the point element C′ with the smallest S and add it to U;

[0031] S33: repeat step S32 with C′ as a new starting point;

[0032] S34: Output the reordered point feature set.

[0033] Optionally, the calculating the difference of coordinate values ​​of adjacent points in the geometric information of the point feature set, line feature, and surface feature, and replacing the original geometric information in a difference manner, includes:

[0034] S41: Calculate the geometric information W' of the point feature set by using the offset subtraction method p [G (i)p |i=1,2,...,n], line feature geometric information W' l [G l,j |j=1,2,...,m], surface element geometric information W' A [G A,k |k=1,2,...,o], the coordinate difference ΔG is calculated as follows:

[0035]

[0036] S42: The coordinates of the first point of the geometric information W remain unchanged, and the coordinates of the subsequent points are replaced by ΔG to obtain new geometric information W", which is expressed as follows:

[0037]

[0038] Among them, W p ″、W l ″、W A ″ respectively represent the new geometric information of point feature set, line feature and surface feature, The difference between the geometric information point coordinates of the i-th point feature and the i-1-th point feature in the table point feature set; ΔG l,j Indicates the difference between the jth and j-1th point coordinates in the line feature geometry information, ΔG A,k Represents the difference between the coordinates of the kth and k-1th points in the geometric information of the surface element.

[0039] Optionally, the geometric information of the converted element is an integer without null values, and its conversion index is equal to the reciprocal of the storage precision T 1 / T, thereby obtaining the final effect of the geometric information of the point element set, line element, and surface element The expression is as follows:

[0040]

[0041] in, Indicates rounding up.

[0042] Compared with the prior art, the advantages of the present invention are:

[0043] (1) The present invention analyzes the field attributes of point, line, and surface elements in geographic information files, and groups and classifies similar elements into sets as needed, thereby increasing the manageability of the files and reducing the complexity of the files;

[0044] (2) The present invention deletes the redundant geometric information generated in the process of vector data file conversion based on the allowable error value, which not only solves the problem of setting the accuracy in the point collection process in the early stage of mapping, but also significantly reduces the file size;

[0045] (3) The present invention stores the geometric coordinates of line elements and surface elements in the form of difference increments, which can greatly simplify the geometric coordinate representation while maintaining the original accuracy;

[0046] (4) The present invention optimizes a path with the shortest interval between discrete disordered point elements, solves the problem of incremental expression of geometric coordinates of point elements, unifies the expression of output vector data files and further reduces file complexity;

[0047] (5) The present invention provides a feasible solution for converting geographic data produced in a stand-alone environment into geographic data suitable for a network environment: lightweight large-volume vector data, reducing the data transmission and rendering pressure on the network side. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a flow chart of a method for lightweight processing of geographic information vector data files of the present invention;

[0049] Figure 2 A schematic diagram for simplifying the attribute expression and grouping of each category of elements in the present invention;

[0050] Figure 3 A schematic diagram of sorting point elements according to the present invention;

[0051] Figure 4 It is a schematic diagram of expressing element geometric information in a difference manner in the present invention;

[0052] Figure 5 This is a partial comparison diagram of the overall route map before and after deleting redundant points in the example of the present invention; the solid points in the figure are sampling points of the original file, the hollow points are the retained points after simplification, and the lines are connected by the retained points. DETAILED DESCRIPTION

[0053] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the examples of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] A lightweight processing method for geographic information vector data files, such as Figure 1 As shown, the implementation steps are as follows:

[0055] S1: Divide geographic information vector data into three categories: point features, line features and surface features, simplify the attribute expression of each category of features and group them.

[0056] The two key parts of the elements are: attributes and geometric information. The present invention first processes the attribute part of the elements. The attribute expression of each category of elements is simplified and grouped as follows: elements with the same reference attribute value are merged to reconstruct a new point element set F. p , line feature set F l , polygon feature set F A , and thus establish the attribute table Q, such as Figure 2 As shown. It is worth noting that the attribute table and feature attributes form a mapping relationship, and the reference attributes of the feature can be simplified to the index value of the attribute table, thereby simplifying the complexity of the attribute expression of the feature. The reference attributes of point, line, and surface features can be freely selected, and the default is all the attributes of the entire layer.

[0057] S2: Delete redundant geometric points of line elements and surface elements under the condition of meeting the allowable error to achieve preliminary simplification of the file.

[0058] The geometric information of point, line and surface elements can be considered from two aspects: the number of points and the point coordinates. The number of points in the geometric information has a greater impact on the file volume, especially for line elements and surface elements composed of a large number of points. This step of deleting redundant geometric points simplifies the number of points in the geometric information of line elements and surface elements. It is worth noting that redundant points refer to points that can be deleted to the maximum extent under the condition of maintaining the overall characteristics and geometric shapes of line elements and surface elements unchanged within the allowable error. The algorithm for filtering redundant points of the present invention adopts the Douglas-Peucker algorithm, which is stable, efficient, easy to implement and has good application range. In addition, the output can be controlled by adjusting the allowable error value, which is very convenient for balancing the simplification effect and fidelity. The specific process of deleting redundant geometric points of line and surface elements is as follows:

[0059] (1) Set the line feature set F l and the polygon feature set F A Simplified tolerance value t;

[0060] (2) Use the Douglas-Peucker algorithm to delete the line feature set F within the allowable error value t l and the polygon feature set F A Redundant geometric coordinate points in the generated simplified line feature set F l ′ and the face element set F A ′.

[0061] The process of Douglas-Peucker algorithm to delete redundant points in feature geometry information is as follows:

[0062] (1) Remove the surface element F A The end point in the geometry information that coincides with the start point, line feature F l The geometric information remains unchanged as the feature to be processed F d ;

[0063] (2)Element F d The geometric information W is composed of points P|(x, y)∈R, and an empty set W′ is created as the new geometric information;

[0064] (3) Factor F d The starting point and the ending point are added to the set W′;

[0065] (4) Connect the coordinate points in the set W to generate a reference line set L;

[0066] (5) Calculate W at the endpoint P of the reference line l∈L s (x s ,y s ), P e (x e ,y e ) The distance D between the point P′(x′,y′) in the middle range and l, and the maximum distance is recorded as D max , and the corresponding point is P m ' ax , where the distance D is calculated as follows:

[0067]

[0068] (6) Compare the maximum distance D max With the allowable error value t: If D max ≤t, then delete all P′; if D max >t, then P m ' ax Insert into the set W′ and repeat steps (4) to (6);

[0069] (7) Redundant points are deleted and W′ is used as the element F dNew geometry information, new line features F l ′ and the new face element F A ′ is processed as follows: Line features can be directly equivalent to F d ; For area elements, F d Perform closing processing, that is, copy F d The starting point of the geometric information W' is inserted at the end as the end point. l ′ and the geometric information W of the surface element A The expression of ′ is as follows:

[0070]

[0071] S3: Reorder the point features based on their geometric distance.

[0072] Point features are different from line features and surface features. Their geometric structure is simple and there is no geometric relationship between them. They are displayed as discrete and disordered in the map. In order to facilitate the subsequent geometric processing of point features, it is necessary to specify the corresponding rules for sorting point features so that they have a certain regularity. The sorting effect is as follows: Figure 3 As shown. The sorting rule of point features is based on the spacing size to match the subsequent steps, so a greedy algorithm can be used. The specific process is as follows:

[0073] (1) Select the point element at the edge corner position in the point element set as the starting point C(x, y) and place it in the new point element set U;

[0074] (2) Calculate the distance S between C and other points, find the point element C′ with the smallest S, and add it to U;

[0075] (3) Repeat step (2) with C′ as the new starting point;

[0076] (4) Output the reordered point feature set.

[0077] S4: Calculate the difference in coordinate values ​​of adjacent points in the geometric information of point feature sets, line features, and surface features, and replace the original geometric information expression with the difference.

[0078] The content expressed by geometric information is generally point coordinates, and this step simplifies the point coordinates. It is worth noting that the necessary condition for expressing the geometric information of elements in a differential manner is that the number of coordinate points contained in the geometric information of the element is two or more. Obviously, line elements and surface elements meet this condition. Although the geometric information of point elements is a single point, it can form the geometric information form of multiple coordinate points in a collection manner, which complements the point element collection generated in step S3.

[0079] The specific operation process of replacing the original geometric information by difference method is as follows:

[0080] (1) Figure 4 As shown, the present invention uses the staggered subtraction method to calculate the geometric information W' of the point element set p [G (i)p |i=1,2,...,n], line feature geometric information W' l [G l,j |j=1,2,...,m], surface element geometric information W' A [G A,k |k=1,2,...,o], the coordinate difference ΔG is calculated as follows:

[0081]

[0082] (2) The coordinates of the first point of the geometric information W remain unchanged, and the coordinates of the subsequent points are replaced by ΔG to obtain the new geometric information W", which is expressed as follows:

[0083]

[0084] Among them, W p ″、W l ″、W A ″respectively represent the new geometric information of point feature set, line feature, and surface feature; Indicates the difference in geometric information point coordinates between the i-th point element and the i-1-th point element in the point element set; ΔG l,j Indicates the difference between the jth and j-1th point coordinates in the line feature geometry information, ΔG A,k Similarly, it represents the difference between the coordinates of the kth and k-1th points in the geometric information of the surface element.

[0085] S5: Convert the geometric information of the features into integers and remove null values ​​to further simplify the file, thereby achieving lightweight geographic information vector data files.

[0086] Among them, the point coordinates of the transformed element geometric information W" are integers without null values, and its conversion index is equal to the reciprocal of the storage precision T 1 / T. Thus, the final effect of the geometric information of the point element set, line element, and surface element is obtained. The expression is as follows:

[0087]

[0088] in, Indicates rounding up.

[0089] The technical effects of the present invention will be verified by specific examples below:

[0090] Example 1:

[0091] Take the route map file "dxf" as an example, its size is 78955KB. This example first uses the geographic information file format conversion tool to automatically extract the original file information and convert it into the commonly used file format "geojson" for vector geographic information. After the conversion, the file size is 79662KB.

[0092] After the file format is converted, when executing step S1 to merge and group the points, lines, and areas, the reference attributes for merging are the design line type, layer name, and style. It is worth noting that the reference attributes can be freely selected.

[0093] In this example, the latitude and longitude accuracy is set to an error of 0.1m. When executing step S2 to delete redundant points in line elements and surface elements, the set allowable error value is based on the latitude and longitude accuracy, that is, t = 10 -6 . Figure 5 The comparative effect of simplifying the line features with this allowable error value is shown. It can be seen that the number of geometric points is significantly reduced while the basic line shape, line topology and display effect are basically maintained as they were.

[0094] It is worth mentioning that the greedy algorithm is used to reorder the point elements of each group. Although the result of the greedy algorithm is a local optimal solution, it has a fast calculation speed and is very suitable for large-scale data.

[0095] The geometric coordinate difference is then represented and quantified according to step S4 and step S5. For example, the original geometric coordinates of a line element are (113.730416, 24.504445), (113.731816, 24.503573), (113.732307, 24.503274), which are converted into (113.730416, 24.504445), (1400, -873), (491, -299).

[0096] Lightweight file Figure 1 The process is carried out, in which the file compression efficiency is most significant after step S2 and step S5, and the lightweight effect is shown in Table 1.

[0097] Table 1 Lightweight effect

[0098] Design Number of geometry points File size / KB Compression % Compression increment% Before lightweight treatment 1098631 79662 - - After step S2 589208 64468 19.07 +19.07 After step S5 589208 8426 89.42 +70.35

[0099] From Table 1, we can see that the compression rate of the lightweight file reaches 89.42%, which is a significant effect. The difference in geometric coordinates indicates that the effect of deleting redundant points is more obvious than that of quantization.

[0100] It is worth noting that if the file size is directly reduced without removing redundant points, that is, step S2 is skipped and the file size generated by steps S1, S3, S4, and S5 is 18362KB, which is (18362-8426) / 8426=117.92% larger than the file size after the complete process. Therefore, if you want to achieve the best reduction effect, you should try to use all the steps of the present invention.

[0101] In this example, a method for lightweight processing of geographic information vector data files provided by the present invention is used to manage the point elements, line elements and surface elements of the route master map data file by grouping and classifying them according to reference attributes; the error tolerance value is determined according to the latitude and longitude accuracy required for mapping, thereby simplifying the geometric information of line elements and surface elements and deleting redundant points; the point elements of each group are reordered according to the greedy algorithm to minimize the geometric spacing of each point element; the geometric information differences of the point, line and surface elements are calculated, and converted into integers to delete null values, thereby further simplifying the route master map file. The present invention performs lightweight processing on files from two main aspects: attribute description and geometric composition: grouping and classification facilitates management while unifying the expression of point, line and surface elements, comprehensively and efficiently improving the operability of the file; geometric simplification significantly reduces the file size, alleviates the pressure of file transmission and the difficulty of post-processing.

[0102] The above description is only a preferred embodiment of the present invention and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention. This specification and the drawings are merely exemplary illustrations of the present invention and are deemed to have covered any and all modifications, variations, combinations or equivalents within the scope of the present invention. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the present invention and its equivalent technologies, the present application is intended to include these modifications and variations.

Claims

1. A method for lightweight processing of geographic information vector data files, characterized in that: The following steps are included: S1: Divide geographic information vector data into three categories: point features, line features, and area features, simplify the attribute expression of each category of features and group them; S2: Delete redundant geometric points of line elements and surface elements under the condition of meeting the allowable error to achieve preliminary simplification of the file; S3: Reorder the point features based on their geometric distance. S4: Calculate the difference between the coordinate values ​​of adjacent points in the geometric information of point feature sets, line features, and surface features, and replace the original geometric information expression with the difference; S5: Convert the geometric coordinates of the features into integers and remove null values ​​to further simplify the file, thereby achieving lightweight geographic information vector data files.

2. The method for lightweight processing of geographic information vector data files according to claim 1, characterized in that: The simplification of attribute expression and grouping of each category of elements includes: merging elements with the same reference attribute value to reconstruct a new point element set F p , line feature set F l , polygon feature set F A , and thus establish the attribute table Q.

3. The method for lightweight processing of geographic information vector data files according to claim 2, characterized in that: The reference attributes of the point features, line features, and area features are freely selected, and the default is all attributes of the entire layer.

4. The method for lightweight processing of geographic information vector data files according to claim 1, characterized in that: The method of deleting redundant geometric points of line elements and surface elements under the condition of satisfying the allowable error includes: S21: Set line feature set F l and the polygon feature set F A Simplified tolerance value t; S22: Use the Douglas-Peucker algorithm to delete the line feature set F within the allowable error value t l and the polygon feature set F A Generate a simplified version of the line feature set F by using the redundant geometric coordinate points in l ′ and the face feature set F A ′.

5. The method for lightweight processing of geographic information vector data files according to claim 4, characterized in that: The process of deleting redundant points in feature geometry information using the Douglas-Peucker algorithm includes: S221: Remove polygon element F A The end point in the geometric information that coincides with the start point, line feature F l The geometric information remains unchanged as the feature to be processed F d ; S222: Element F d The geometric information W is composed of points P|(x,y)∈R, and an empty set W′ is created as the new geometric information; S223: Element F d The starting and ending points of are added to the set W′: S224: Connect the coordinate points in the set W to generate a reference line set L; S225: Calculate W at the endpoint P of the reference line l∈L s (x s ,y s ), P e (x e ,y e ) The distance D between the point P′(x′,y′) in the middle range and l, the maximum distance is recorded as D max , the corresponding point is P m ' ax , where the distance D is calculated as follows: S226: Compare the maximum distance D max With the allowable error value t: If D max ≤t, then delete all P′; if D max >t, then P m ' ax Insert it into the set W′ and repeat steps S224 to S226; S227: Redundant points are deleted and W′ is used as the element F d New geometry information.

6. The method for lightweight processing of geographic information vector data files according to claim 5, characterized in that: The new line element F in step S227 l ′ and the new face element F A 'Processing includes: Line features are directly equivalent to F d ; Area elements need to be F d Perform closing processing, including: copying F d The starting point of the geometric information W′ is inserted to the end as the end point, and the final line element geometric information W l ′ and the geometric information W of the surface element A ′ is expressed as follows:

7. The method for lightweight processing of geographic information vector data files according to claim 1, characterized in that: The point elements are reordered based on the geometric distance of the point elements, including: S31: Select a point feature at an edge corner position in the point feature set as the starting point C(x, y) and place it in the new point feature set U; S32: Calculate the distance S between C and other points, find the point element C′ with the smallest S and add it to U; S33: Repeat step S32 with C′ as the new starting point; S34: Output the reordered point feature set.

8. The method for lightweight processing of geographic information vector data files according to claim 1, characterized in that: The calculation of the difference between the coordinate values ​​of adjacent points in the geometric information of the point feature set, line feature, and surface feature, and replacing the original geometric information with the difference, includes: S41: Calculate the geometric information W' of the point feature set by using the offset subtraction method p [G (i)p |i=1,2,...,n], line feature geometric information W' l [G l,j |j=1,2,...,m], surface feature geometric information W' A [G A,k The coordinate difference ΔG of |k=1,2,...,o] is calculated as follows: S42: The coordinates of the first point of the geometric information W remain unchanged, and the coordinates of the subsequent points are replaced by ΔG to obtain the new geometric information W", which is expressed as follows: Among them, W″ p , W″ l , W″ A Respectively represent the new geometric information of point feature sets, line features, and surface features. The difference in geometric information point coordinates between the i-th point feature and the i-1-th point feature in the table point feature set; ΔG l,j Indicates the difference between the coordinates of the jth and j-1th points in the line feature geometry, ΔG A,k Represents the difference between the coordinates of the kth and k-1th points in the geometric information of the surface feature.

9. The method for lightweight processing of geographic information vector data files according to claim 1, characterized in that: The geometric information of the conversion element is an integer without null values, and its conversion index is equal to the reciprocal of the storage precision T 1 / T, thereby obtaining the final effect of the geometric information of the point element set, line element, and surface element. The expression is as follows: in, Indicates rounding up.

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