An electronic chart topology automatic construction method

Abstract

The application relates to an electronic chart topology automatic construction method, and belongs to the technical field of marine surveying and mapping. The method comprises the following steps: constructing an element table, an attribute table and a spatial geometry topology table according to the geometric type of elements; importing element, geometry and attribute data into corresponding table structures; performing a de-duplication processing based on a buffer threshold on a point topology table; breaking and reconstructing curves intersecting with the point buffer in the curve topology table; merging overlapping curves in the curve topology table; and merging overlapping surfaces in the surface topology table. The application realizes the topology consistency construction of the elements of the electronic chart at the physical geometry level, meets the S-101 standard requirements, has the characteristics of flexibility, openness and easy integration into a basic geographic information platform, and effectively improves the automation degree and data quality of the production of the electronic chart.

Description

Technical Field

[0001] This invention belongs to the field of marine surveying and mapping technology, and in particular to an automatic method for constructing the topology of electronic nautical charts. Background Technology

[0002] In mathematics, "topology" refers to the characteristics of a graph (or set) that remain unchanged under continuous deformation. "Map topology," a concept in cartography and geographic information systems, refers to the sum of stable spatial relationships (such as coincidence, adjacency, containment, and connection) between spatial geometric instances (such as points, lines, and polygons) after ignoring their specific geometric details (such as length, area, and coordinate position). "Topology editing" refers to various graphic and relational operations applied to spatial geometric instances to construct a map topology that meets requirements. For example, it involves constructing two line features with a coincident relationship into the same set of connected edges and nodes, thereby ensuring the accuracy and consistency of map topological relationships.

[0003] In map topology, spatial geometry is often abstracted into geometric simplexes and geometric complexes. A geometric simplex refers to a single, connected, and homogeneous geometric object in space; a geometric complex is a set of separate geometric simplexes, where the boundary of each simplex can be expressed as a union of other geometric simplexes with lower dimensions within the set. In two-dimensional space, spatial geometry can be divided into three types of geometric simplexes based on their dimension: points, curves, and surfaces. Based on different spatial geometric organization methods and constraints, five topological levels can be defined: 1. Level 1. Unconstrained, consisting of a set of independent points and curves: curves have no reference points (no boundaries), points and curves may repeat; a region is represented by a closed curve. This level can be simply referred to as "topologically unrestricted".

[0004] 2. Level 2a. Consists of a set of point and curve simplexes conforming to the following constraints: Each curve must reference a start point and an end point (which may be the same); curves must not self-intersect; the region is represented by a closed curve, and the start and end points are common points; for regions with holes, all internal boundaries must be completely contained within the external boundaries, and internal boundaries cannot intersect with other internal or external boundaries. Internal boundaries may be tangent to other internal or external boundaries (i.e., at a single point); the outer boundary of the surface must be clockwise (the surface is to the right of the curve), and the direction of the curve must be positive; the inner boundary of the surface must be counterclockwise (the surface is to the right of the curve), and the direction of the curve must be negative. This level can be simply referred to as "point chain topology".

[0005] 3. Level 2b. Consists of a set of point and curve simplexes that meet the following constraints: In addition to Level 2a, the following constraints are added: Each set of simplexes must form a geometric complex; curves cannot self-intersect if no points at their intersections are referenced; multiple coincident geometries are not allowed. This level can be simply referred to as "planar topology".

[0006] 4. Level 3a. Consists of a set of points, curves, and surface simplexes that comply with the following constraints: Level 2a constraints apply.

[0007] 5. Level 3b. Consists of a set of point, curve, and surface simplexes that conform to the following constraints: Building upon Levels 2a and 2b, the following constraints are added: surfaces must be mutually exclusive, and they must provide a complete spatial cover. This level may be simply referred to as "complete topology".

[0008] In the 1980s and 90s, when digital mapping was still in its infancy, many applications adopted data models with topological constraints to reduce storage space. A typical example is the Coverage data model in ESRI's ArcInfo software, which is essentially a "complete topology." Due to the huge success of ArcInfo software in its global rollout, the Coverage data model was widely recognized and used for a long time, and most people equated "topology" with the Coverage data model. However, building a Coverage data model requires maintaining and updating very complex topological relationship tables, such as "face-face," "face-edge," and "edge-edge" relationship tables, making it very difficult to build a robust and practical topology editing software. In the 21st century, ArcInfo has been upgraded to ArcMap, which no longer supports the Coverage data model. It no longer requires explicitly defining and maintaining complex topological relationship tables. Instead, it adopts an object-oriented data model and predefined topology rules to achieve "instant" topology consistency checks at the feature object level, that is, to achieve logical consistency rather than physical spatial geometry consistency, or to achieve topology editing by building temporary "point-edge" topology relationships.

[0009] Nautical charts are a type of map that follows the shape of the land. Figure 1While possessing general theoretical frameworks, electronic nautical charts (ENATs) also have specific conventions and exhibit significant international characteristics. Their development is guided and influenced by international hydrographic organizations. For example, current ENAT data exchange formats must conform to the S-57 standard, with a topology level of 2a; while the next-generation ENAT exchange format must conform to the S-101 standard, with a topology level of 3a. The topology level of ENAT data differs from that of Coverage, and to date, topological consistency at the physical spatial geometric level is still required. Therefore, neither ArcInfo nor ArcMap currently supports the standardized production of ENATs. Globally, achieving topology editing of ENATs is a highly specialized technical issue. Currently, only a very few ENAT production software programs possess this capability, such as Caris and dKart. However, these software programs are specifically designed for ENATs, and their complex internal business logic makes them difficult to integrate into basic geographic information platforms, thus limiting the integration of ENATs into the mainstream geographic information industry. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of the prior art and propose an automatic construction method for electronic nautical chart topology. Compared with traditional technology, it has the characteristics of flexibility, openness and ease of implementation, and can be integrated and applied in basic geographic information platforms.

[0011] The technical problem solved by this invention is achieved through the following technical solution: A method for automatically constructing the topology of an electronic nautical chart, characterized by comprising the following steps: Step S1: Based on the geometric type of the electronic nautical chart elements, construct an element table, an attribute table, and a spatial geometric topology table; the spatial geometric topology table includes a point topology table, a curve topology table, a composite curve topology table, and a surface topology table, which are used to store automatically constructed topology information and realize the initial construction of the topology structure; Step S2: Import the feature data, geometric data, and attribute data to be constructed into the table constructed in step S1; Step S3: Perform deduplication processing on the point topology table described in Step 2, eliminate redundant points and update associated references to complete the automatic construction of the point topology; Step S4: Break the curves that intersect with the point buffer in the curve topology table described in Step 2, and update the composite curves and surface references to complete the automatic construction of some new curves and composite curves. Step S5: Merge the overlapping curves in the curve topology table described in Step 2, update the associated topology structure, and complete the automatic construction of the remaining curves and combined curves. Step S6: Merge the overlapping surfaces in the surface topology table described in Step 2, update the reference relationship between features and geometry, and complete the automatic construction of surface topology.

[0012] Furthermore, the point topology table is used to store the unique identifier and geometric coordinates of a point; The curve topology table is used to store the unique identifier, geometric coordinates, start endpoint identifier, and end endpoint identifier of the curve. The combined curve topology table is used to store the unique identifier of the combined curve and the list of curve identifiers and directions it references; The surface topology table is used to store the unique identifier of the surface, the identifier of the referenced curve or composite curve, the reference type, direction, and inner and outer loop indication information.

[0013] Moreover, step S2 includes: For point features, their geometry is stored in the point topology table, and the one-to-one correspondence between features and geometry is recorded in the feature and topology relationship table. For line features, store their first and last points in the point topology table, store the remaining geometric points in the curve topology table, record the reference relationship between the curve and the endpoints, and record the one-to-one correspondence between line features and curves in the feature and topology relationship table. For polygon features, their geometry is stored in the curve topology table. If an inner loop exists, a one-to-many correspondence and inner / outer loop identifiers are recorded in the feature-topology relationship table; otherwise, a one-to-one correspondence is recorded.

[0014] Moreover, step S3 includes: setting a point buffer threshold and identifying points in the point topology table whose distance is less than the threshold as overlapping points; Keep one point, mark the remaining overlapping points as deleted, and record the index of the kept point; Update the references to the corresponding points in the curve topology table; Update the references of the corresponding points in the feature and topology table.

[0015] Furthermore, step S4 includes: setting a threshold for the distance buffer between points and curves, and identifying the intersection relationship between points in the point topology table and curves in the curve topology table; At the intersection point, break the curve into two new curves and update the curve topology table; Create a composite curve that references a new curve, and update the composite curve topology table. Update the surface topology table and the references to the corresponding curves in the feature and topology relationship table.

[0016] Moreover, step S5 includes: setting a curve distance threshold and identifying geometrically overlapping curves in the curve topology table; If they completely overlap, keep one curve, mark the rest as deleted, and update the references; If there is partial overlap, insert a point at the separation point and extract the overlapping part as a new curve, then update the point and curve topology table; Update the curve references in the composite curve topology table, surface topology table, and feature and topology relationship table.

[0017] Furthermore, step S6 includes: identifying surfaces in the surface topology table that are composed of the same curves as overlapping surfaces; Keep one of the surfaces and mark the rest as deleted; Update the references to the corresponding surfaces in the feature and topology relationship table.

[0018] The advantages and positive effects of this invention are: This invention, through the ingenious design of tables such as feature tables, attribute tables, and spatial geometric topology tables, enables topology editing without altering the internal data model and business logic of the basic geographic information platform. Furthermore, because the topology structure is explicitly stored, topology data can be flexibly and conveniently queried, exported, or optimized, thus decoupling the topology structure from the basic geographic information platform. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the electronic nautical chart topology of the present invention; Figure 2 This is a schematic diagram illustrating the relationship between electronic chart elements and topology in this invention; Figure 3 This is a record of the water depth point element table of the present invention; Figure 4 This is a diagram illustrating the water depth point elements of the present invention; Figure 5 This is a topology table record for the points in this invention; Figure 6 This is a record of the UnderwaterAwashRock element table of the present invention; Figure 7 This is a record of the spatial relationship between the elements of this invention; Figure 8 This is a diagram illustrating the reef elements of the present invention; Figure 9 This is a topology table record for the points in this invention; Figure 10 This is a record of the curve topology table of the present invention; Figure 11 This is a record of the Coastline element table of the present invention; Figure 12 This is a record of the spatial relationship between the elements of this invention; Figure 13 This is a diagram illustrating the Coastline elements of the present invention; Figure 14 This is a topology table record for the points in this invention; Figure 15 This is a record of the curve topology table of the present invention; Figure 16 This is a record of the surface topology table of the present invention; Figure 17 This is a record of the LandArea element table in this invention; Figure 18 This is a record of the spatial relationship between the elements of this invention; Figure 19 This is a diagram illustrating the LandArea elements of the present invention; Figure 20 This is a schematic diagram of the invention before deduplication. Figure 21 This is a schematic diagram of the deduplication process for the present invention. Figure 22 This is a schematic diagram of the curve before it is broken in this invention; Figure 23 This is a record of the curve topology table of the present invention; Figure 24 This is a record of the combined curve topology table of the present invention; Figure 25 This is a record of the surface topology table of the present invention; Figure 26 This is a schematic diagram of the curve after it has been broken according to the present invention; Figure 27 This is a schematic diagram of the curves before merging in this invention; Figure 28 This is a schematic diagram of the curves after merging according to the present invention; Figure 29 This is a schematic diagram of the surface before merging in this invention; Figure 30 This is a schematic diagram of the surface merging process of the present invention; Figure 31 The diagram shows the topology after importing the elements of this invention and automatically building the topology. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the accompanying drawings.

[0021] A method for automatically constructing the topology of an electronic nautical chart, characterized by comprising the following steps: Step S1: Based on the geometric type of the electronic nautical chart elements, construct the element table, attribute table, and spatial geometric topology table; the spatial geometric topology table includes the point topology table, curve topology table, composite curve topology table, and surface topology table.

[0022] A point topology table is used to store the unique identifier and geometric coordinates of a point; The curve topology table is used to store the unique identifier, geometric coordinates, start endpoint identifier, and end endpoint identifier of a curve. The composite curve topology table is used to store the unique identifier of the composite curve and the list of curve identifiers and directions it references; The surface topology table is used to store the unique identifier of the surface, the identifier of the referenced curve or composite curve, the reference type, direction, and inner and outer loop indication information.

[0023] Step S2: Import the feature data, geometric data and attribute data to be constructed into the table constructed in step S1.

[0024] Store the water depth point features separately as a water depth point feature table (multiple points); store the source data point features, line features, and polygon features and their attributes into the corresponding feature tables (each feature type corresponds to one feature table) and topology table in sequence; store the spatial geometry of point features, line features, and polygon features into the topology table; store the relationship between features and spatial geometry into the feature-topology relationship table.

[0025] For all point feature spatial geometry, store them in the point topology table, and store the one-to-one correspondence between features and topology relationships in the feature-topology relationship table; for all line feature spatial geometry, store their first and last points in the point topology table, store the remaining points in the curve topology table, store the reference relationship between curves and their first and last points, and store the one-to-one correspondence between line features and curves in the feature-topology relationship table; for all polygon feature spatial geometry, store them in the curve topology table. If a polygon feature has an inner loop, store its one-to-many correspondence and inner / outer loop indicator in the feature-topology relationship table; otherwise, store its one-to-one correspondence in the feature-topology relationship table.

[0026] Step S3: Perform deduplication processing on the point topology table to eliminate redundant points and update associated references.

[0027] Set a point buffer threshold, identify points whose spatial distance is within the buffer threshold as overlapping points, retain the first point, mark the remaining duplicate points as deleted, and note the index position of the retained point in each duplicate point record; update the endpoint reference record of the curve topology table; traverse the feature and topology relationship table, and update the reference record pointing to the duplicate point to point to the retained point.

[0028] Step S4: Break the curves that intersect with the point buffer in the curve topology table, and update the composite curve and surface references.

[0029] Set a threshold for the distance buffer between points and curves. Using points Pnt in the point topology table, determine their spatial relationship with a curve CurveOne in the curve topology table. Use Pnt to disconnect CurveOne, creating two curve records, Curve1 and Curve2. Replace CurveOne with Curve1 and Curve2 in the curve topology table and update its endpoint reference records. Construct a composite curve record CurveComposite, referencing Curve1 and Curve2. Find feature records in the feature and topology relationship table that reference curve Curve, and update these references to CurveComposite. Search the composite curve topology table for possible CurveCompositeMaybe records referencing CurveOne; if found, reorganize their curve composition relationships. Update the surface topology table.

[0030] Step S5: Merge the overlapping curves in the curve topology table and update the associated topology structure.

[0031] In step 4, if point Pnt is outside the curve, a curve distance threshold is set, and overlapping geometry in the curve topology table is identified. If it is a complete overlap, the first curve is retained, the remaining duplicate curves are marked for deletion, and the index position of the retained curve is noted in each duplicate curve record. If it is a partial overlap, a point is inserted at the separation point and added to the point topology table, and the overlapping part is extracted as a new curve CurveNew. Deduplication is performed on the point topology table and the curve topology table; the combined curve topology table, surface topology table, and feature and topology relationship table are updated.

[0032] Step S6: Merge the overlapping surfaces in the surface topology table and update the reference relationship between features and geometry.

[0033] Surfaces in the surface topology table that are composed of the same curves are identified as overlapping surfaces. The first surface is retained, and the remaining duplicate surfaces are marked for deletion. The index position of the retained surface is noted in each duplicate surface record. The overlapping surfaces are deduplicated, and the feature and topology relationship table is updated.

[0034] Based on the above-mentioned method for automatically constructing the topology of electronic nautical charts, calculations were performed to verify the effectiveness of the invention.

[0035] Step 1: Construct corresponding feature, attribute, and spatial geometry topology tables based on different feature geometry types.

[0036] Topological data structures include four types of topological units: points, curves, composite curves, and surfaces. Figure 1As shown, the geometric relationships within a topological unit are as follows: curves are composed of control points, excluding endpoints; surfaces are composed of several curves or composite curves; there is a one-to-many relationship between composite curves and curves, and also a one-to-many relationship between surfaces and composite curves or curves; endpoints participate in the formation of curves as topological units, while ordinary control points only have geometric significance and do not participate in topological construction.

[0037] like Figure 2 As shown, electronic nautical chart elements, through structured storage, fully record information such as element metadata, attributes, geometry, topology, and relationships.

[0038] Each point record in the point topology table contains the (end) point's ID and geometry.

[0039] Each curve record in the curve topology table contains the curve's ID, the curve's geometry, the start endpoint ID of the curve reference, and the end endpoint ID of the curve reference.

[0040] Each composite curve in the composite curve topology table consists of one or more records. Each record contains the ID of the composite curve, a list of curve IDs referenced by the composite curve, the ID of each referenced curve, and the direction of the referenced curve. The complete geometry of the composite curve can be logically assembled through the geometry and direction of the curves it references.

[0041] Each surface in the surface topology table consists of one or more records. Each record contains the surface ID, the ID of the curve or composite curve referenced by the surface, the reference type, the curve direction, and inner / outer loop indication information. Reference types include curve type and composite curve type; curve direction includes positive and negative types; inner / outer loop indication includes inner loop and outer loop types. The complete geometry of a surface can be logically constructed using the geometry and direction information of the curves it references.

[0042] Step 2: Import the feature data, geometric data, and attribute data to be constructed into the feature, attribute, and spatial geometric topology table created in Step 1.

[0043] (1) Import water depth point elements (multi-point) The source data is a point-type SHP file named Sounding.shp, whose geometric three-dimensional coordinates represent the position and depth of each water depth point. The attribute fields include qualityOfVerticalMeasurement and techniqueOfVerticalMeasurement.

[0044] During import, the geometric and attribute information is directly imported into the Sounding feature table for water depth points. Key information includes RCID (feature code), SmGeometry (coordinate information), and ATTR (attribute information), with the SmGeometry field stored in binary format. The imported data table looks like this. Figure 3 As shown.

[0045] like Figure 4 The image shows how the water depth point element is displayed.

[0046] (2) Importing point elements The source data is a point-type SHP file named UnderwaterAwashRock.shp, whose geometric coordinates represent the location of each reef, and the attribute fields include qualityOfVerticalMeasurement, valueOfSounding, waterLevelEffect, and surroundingDepth.

[0047] like Figure 5 As shown, during import, a point is first added to the geometry point table All_Points, and the main information includes RCID (geometric code) and SmGeometry (coordinate information).

[0048] Then, as Figure 6 As shown, add a feature to the UnderwaterAwashRock feature table. The main information includes RCID (feature code) and ATTR (attribute information).

[0049] Finally, as Figure 7 As shown, it is necessary to establish feature-geometric associations. Add records to the Feature-Geometric Associations table FVSO, with key information including CODE (feature type code), RCID (feature code), RRID (associated geometry code), RRNM (geometric type code), and ORNT (reference direction).

[0050] like Figure 8 The image shows how the reef element is displayed.

[0051] (3) Importing line elements The source data is a line-type SHP file Coastline.shp, whose line coordinates represent the position and shape of each coastline, and the attribute field includes categoryOfCoastline.

[0052] When importing, such as Figure 9 As shown, first, the first and last endpoints of the coastline are added to the geometry point table All_Points. The main information includes RCID (geometric code) and SmGeometry (coordinate information).

[0053] Then, as Figure 10 As shown, a curve is added to the All_Curves table of geometric curves. The main information includes RCID (geometric code), SmGeometry (coordinate information), STARTNODEID (start endpoint code), and ENDNODEID (end endpoint code). The codes of the start and end endpoints directly reference the codes of the geometric points added in the previous step.

[0054] Next, as Figure 11 As shown, a new feature is added to the Coastline feature table. The main information includes RCID (feature code) and ATTR (attribute information).

[0055] Finally, as Figure 12 The diagram shows the need to establish feature-geometric associations. Add records to the Feature-Geometric Associations (FVSO) table, including key information such as CODE (feature type code), RCID (feature code), RRID (associated geometry code), RRNM (geometric type code), and ORNT (reference direction).

[0056] like Figure 13 The image shows how the coastline features are displayed.

[0057] (4) Importing surface features The source data is a polygon-type SHP file, LandArea.shp, whose coordinates represent the location and shape of each land area, and the attribute field includes featureName.

[0058] When importing, such as Figure 14 As shown, first, add the endpoint of the outer ring of the land area to the geometry point table All_Points. The main information includes RCID (geometric code) and SmGeometry (coordinate information). The outer ring is closed, so only one endpoint needs to be added.

[0059] Then, as Figure 15 As shown, a curve is added to the All_Curves table of geometric curves. The main information includes RCID (geometric code), SmGeometry (coordinate information), STARTNODEID (start endpoint code), and ENDNODEID (end endpoint code). The codes of the start and end endpoints directly reference the codes of the geometric points added in the previous step.

[0060] Next, as Figure 16 As shown, a record is added to the SurfaceCurveLink table. The main information includes RCID (geometric code), RRID (associated geometric code), RRNM (associated geometric type code), and ORNT (reference direction).

[0061] Continue, as Figure 17 As shown, a new feature is added to the LandArea feature table. The main information includes RCID (feature code) and ATTR (attribute information).

[0062] Finally, as Figure 18 As shown, it is necessary to establish feature-geometric associations. Add records to the Feature-Geometric Associations table FVSO, with key information including CODE (feature type code), RCID (feature code), RRID (associated geometry code), RRNM (geometric type code), and ORNT (reference direction).

[0063] like Figure 19 The image shows how land area elements are displayed.

[0064] Step 3: Perform deduplication processing on the topology table corresponding to the points in Step 1.

[0065] Set the point buffer threshold T to 0.000001. When the distance between two points is less than this value, they are considered to be overlapping.

[0066] like Figure 20 As shown, the tail end of river 650, the head end of river 651, and reef 128 reference three different geometric points 386, 388, and 387, respectively. Calculations show that the distance between these three points is less than the threshold T, therefore they are determined to overlap, and deduplication is required. The execution process is as follows: (1) Keep the first point and mark the remaining duplicate points as deleted: Keep geometric point 386, and mark the other two geometric points 388 and 387 as deleted.

[0067] (2) Update the endpoint reference records in the curve topology table: Update the curve table All_Curves, changing the starting endpoint reference of the curve with RCID=338, i.e., the value of the STARTNODEID field, from 388 to 386.

[0068] (3) Point reference records in the element and topology relationship table: Update the feature geometry association table FVSO, changing the point reference (RRID) of the reef feature with RCID=128 from 387 to 386.

[0069] (4) Delete the remaining duplicates: Update the point table All_Points and delete the points with RCID=387 and RCID=388.

[0070] like Figure 21As shown, after deduplication, the above three elements achieve a common topology, resulting in a redrawn graphic effect.

[0071] Step 4: Break the curves that intersect with the buffer of the point within the threshold range in the topology table corresponding to the curve in Step 1.

[0072] Set the threshold T for the point-curve buffer to 0.000001. When the distance from a point to a curve is less than this value, the point is determined to be on the curve.

[0073] like Figure 22 As shown, the distance between the tail endpoint 719 of curve 733 and the outer loop curve 437 of surface 65 is 0.000000012, which is less than the threshold T. Therefore, it is determined that the endpoint is on the outer loop of the surface. The system performs the following processing: (1) Disrupt curve 437 like Figure 23 As shown, curve 437 is broken at endpoint 719, generating two new curves 731 (first endpoint 512, last endpoint 719) and 732 (first endpoint 719, last endpoint 512). They both reference endpoint 719, forming a common topology.

[0074] (2) Construct a combined curve using new curves 731 and 732. like Figure 24 As shown, in the ComplexCuveLink table, add a composite curve 121, which is associated with two curves 731 and 732. The reference direction ORNT is equal to 1 for positive.

[0075] (3) Update the relationship between surface 65 and composite curve 121. like Figure 25 As shown, modify the SurfaceCurveLink table to change the associated curve code RRID of the record with RCID=65 to 121 and RRNM to 125, which is the combined curve.

[0076] (4) Update the geometric association of features Change all elements of the original curve 437 to the composite curve 121.

[0077] Query the feature geometric association table FVSO and change the records with RRID=437 and RRNM=120 to RRID=121 and RRNM=125.

[0078] (5) Delete the original curve 437 like Figure 26 As shown, after the above processing, there are no elements or geometric reference curves 437 left, therefore, they are deleted from the All_Curves table.

[0079] Step 5: Merge the overlapping curves in the topology table corresponding to the curves in Step 1.

[0080] The curve distance threshold T is set to 0.000001. When the distance between all points on two curves is less than this value, they are considered to overlap.

[0081] like Figure 27 As shown, surface 172 references curve 115, coastline 771 references curve 116, and composite curve 125 references curve 117. After calculating the curve buffer distance, the distance between these three curves is less than the threshold T, therefore they are determined to overlap, and deduplication processing needs to be performed. The execution process is as follows: (1) Keep the first curve and mark the remaining repeating curves as deleted: Curve 115 is retained, while the other two curves, 116 and 117, are marked for deletion.

[0082] (2) Update the composite curve topology table: Update the ComplexCurveLink table to reference the combined curve with RCID=125 and RRID=117. That is, change the RRID field value from 117 to 115.

[0083] (3) Update the surface topology table: Update the SurfaceCurveLink table, changing the record with RRID=117 to 115.

[0084] (4) Update the feature and topology relationship table: Update the feature geometry association table FVSO, changing the curve reference of the coastline feature with RCID=771, i.e., the RRID value, from 116 to 115.

[0085] (5) Delete the remaining duplicate curves: Update the curve table All_Curves and delete the curves with RCID=116 and RCID=117.

[0086] After deduplication, the above three elements achieve a shared edge topology, and the redrawn graphic effect is as follows: Figure 28 .

[0087] Step 6: Merge the overlapping surfaces in the topology table corresponding to the surfaces in Step 1.

[0088] Two surfaces are considered to overlap if they are composed of the same curves.

[0089] like Figure 29As shown, depth region 1132 references surface 200, lake 1131 references surface 201, and both surfaces reference the same curve 121, therefore they are determined to overlap. Deduplication is required. The execution process is as follows: (1) Keep the first surface and mark the remaining duplicate surfaces as deleted: Keep surface 200, and mark surface 201 as deleted.

[0090] (2) Update the feature and topology relationship table: Update the feature geometry association table FVSO, changing the surface reference (RRID) of the lake feature with RCID=1131 from 201 to 200.

[0091] (3) Delete the remaining duplicate surfaces: Update the SurfaceCurveLink table and delete the surface with RCID=201.

[0092] After deduplication, the two elements mentioned above share the same curve, and the redrawn graphic effect is as follows. Figure 30 As shown.

[0093] After importing various types of elements, including points, curves, and surfaces, along with their attributes, the system automatically constructs the geometric topology through the aforementioned processing. It removes overlapping points, curves, and surfaces, and establishes correct reference relationships between elements and geometry, as well as between geometric shapes. The resulting nautical chart, after rendering and graphical representation, displays as follows: Figure 31 As shown.

[0094] It should be emphasized that the embodiments described in this invention are illustrative rather than limiting. Therefore, this invention includes, but is not limited to, the embodiments described in the specific implementation. Any other implementations derived by those skilled in the art based on the technical solutions of this invention are also within the scope of protection of this invention.

Claims

1. A method for automatically constructing the topology of an electronic nautical chart, characterized in that, Includes the following steps: Step S1: Based on the geometric type of the electronic nautical chart elements, construct the element table, attribute table, and spatial geometric topology table; The spatial geometric topology table includes a point topology table, a curve topology table, a composite curve topology table, and a surface topology table, which are used to store automatically constructed topology information and realize the initial construction of the topology structure. Step S2: Import the feature data, geometric data, and attribute data to be constructed into the table constructed in step S1; Step S3: Perform deduplication processing on the point topology table described in Step 2, eliminate redundant points and update associated references to complete the automatic construction of the point topology; Step S4: Break the curves that intersect with the point buffer in the curve topology table described in Step 2, and update the composite curves and surface references to complete the automatic construction of some new curves and composite curves. Step S5: Merge the overlapping curves in the curve topology table described in Step 2, update the associated topology structure, and complete the automatic construction of the remaining curves and combined curves. Step S6: Merge the overlapping surfaces in the surface topology table described in Step 2, update the reference relationship between features and geometry, and complete the automatic construction of surface topology.

2. The method for automatically constructing the topology of an electronic nautical chart according to claim 1, characterized in that, In step S1: the point topology table is used to store the unique identifier and geometric coordinates of a point; The curve topology table is used to store the unique identifier, geometric coordinates, start endpoint identifier, and end endpoint identifier of the curve. The combined curve topology table is used to store the unique identifier of the combined curve and the list of curve identifiers and directions it references; The surface topology table is used to store the unique identifier of the surface, the identifier of the referenced curve or composite curve, the reference type, direction, and inner and outer loop indication information.

3. The method for automatically constructing the topology of an electronic nautical chart according to claim 1, characterized in that, Step S2 includes: For point features, their geometry is stored in the point topology table, and the one-to-one correspondence between features and geometry is recorded in the feature and topology relationship table. For line features, store their first and last points in the point topology table, store the remaining geometric points in the curve topology table, record the reference relationship between the curve and the endpoints, and record the one-to-one correspondence between line features and curves in the feature and topology relationship table. For polygon features, their geometry is stored in the curve topology table. If an inner loop exists, a one-to-many correspondence and inner / outer loop identifiers are recorded in the feature-topology relationship table; otherwise, a one-to-one correspondence is recorded.

4. The method for automatically constructing the topology of an electronic nautical chart according to claim 1, characterized in that, Step S3 includes: setting a point buffer threshold and identifying points in the point topology table whose distance is less than the threshold as overlapping points; Keep one point, mark the remaining overlapping points as deleted, and record the index of the kept point; Update the references to the corresponding points in the curve topology table; Update the references of the corresponding points in the feature and topology table.

5. The method for automatically constructing the topology of an electronic nautical chart according to claim 1, characterized in that, Step S4 includes: setting a threshold for the distance buffer between points and curves, and identifying the intersection relationship between points in the point topology table and curves in the curve topology table; At the intersection point, break the curve into two new curves and update the curve topology table; Based on the two broken new curves, construct a new combined curve and update the combined curve topology table. Update the surface topology table and the corresponding curve references in the feature and topology relationship table.

6. The method for automatically constructing the topology of an electronic nautical chart according to claim 1, characterized in that, Step S5 includes: setting a curve distance threshold and identifying geometrically overlapping curves in the curve topology table; If they completely overlap, keep one curve, mark the rest as deleted, and update the references; If there is partial overlap, insert a point at the separation point and extract the overlapping part as a new curve, then update the point and curve topology table; Update the curve references in the composite curve topology table, surface topology table, and feature and topology relationship table.

7. The method for automatically constructing the topology of an electronic nautical chart according to claim 1, characterized in that, Step S6 includes: identifying surfaces in the surface topology table that are composed of the same curves as overlapping surfaces; Keep one of the surfaces and mark the rest as deleted; Update the references to the corresponding surfaces in the feature and topology relationship table.

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