A Method and System for Fitting 3D Terrain Entities with Smooth Non-uniform Rational B-Splines

Abstract

This invention provides a method and system for fitting and creating smooth, non-uniform rational B-spline 3D terrain entities, primarily applied in pumped storage power station engineering, achieving efficient conversion from 2D contour lines to smooth terrain entities. The method involves establishing a triangular mesh surface, specifying boundaries, converting DEM data, creating a raster surface, extracting control points, and fitting NURBS curves along the UV direction to ultimately generate a NURBS terrain entity. The process involves converting contour lines to DEM data and creating a raster surface; extracting control points and fitting NURBS curve sets along the U / V directions; and forming a complete NURBS 3D terrain entity by enclosing the surface surface, bottom plane, and four side surfaces. This invention allows for on-demand adjustment of terrain accuracy, the generated entity can be directly used for CAE simulation calculations, and can be combined with panel dam zoning calculation algorithms to improve engineering design efficiency.

Description

Technical Field

[0001] This invention relates to the field of pumped storage power station engineering technology, and in particular to a method and system for creating smooth, non-uniform rational B-spline three-dimensional terrain entities through fitting. Background Technology

[0002] Non-uniform rational B-splines are an excellent modeling method supported by advanced 3D software. They offer better control over the curvature of object surfaces compared to traditional mesh modeling, resulting in more realistic and vivid shapes. In engineering design, especially in hydraulic and hydropower projects, the ability to quickly, efficiently, and smoothly fit 3D terrain entities is crucial for BIM digital design. While Civil 3D, a 3D civil engineering design software, can quickly fit terrain triangular mesh surfaces and directly extrude 3D terrain entities from these surfaces, in practical engineering applications, because these 3D terrain entities are not smooth but rather formed by directly extruded numerous triangular patches, many redundant lines appear during model sectioning and display, thus affecting the model's usability.

[0003] Existing technology one, Chinese patent, patent number: 202110127452.6, belongs to the technical field of geological modeling, specifically involving a BIM-based automatic 3D geological modeling method. This method includes acquiring multi-source geological exploration data, performing data fusion processing on the multi-source geological exploration data, representing topographic surfaces and various stratigraphic interfaces using non-uniform rational B-spline surfaces, analyzing the multi-source geological exploration data to obtain the stratigraphic sequence rules of various strata, determining the Boolean logic operation order between various stratigraphic interfaces and the 3D geological model based on the stratigraphic sequence rules, obtaining the generation logic of the 3D geological model, performing parametric geological modeling, and enabling real-time updates of the 3D geological model and its various output files for different uses, outputting the required 3D geological model. While this method achieves real-time updates of the stratigraphic model globally or locally, automates the modeling process, and implements parametric modeling—a multi-party collaborative modeling method—it lacks parametric modeling capabilities.

[0004] Prior art two, Chinese patent, patent number: 202510218626.8, relates to the field of bridge modeling technology, and discloses a long-distance bridge modeling method based on Civil 3D, Revit, and Dynamo. The method includes step 1: constructing the bridge centerline using Civil 3D, generating a set format, and importing it into a Revit project; streamlining the bridge modeling process, dividing the required components into layout components and adaptive components; calculating the point information required for adaptive components; establishing layout component families and adaptive component families respectively and importing them into the project; using Dynamo in Revit to convert the centerline into a spline curve; and using Dynamo to batch place layout components and adaptive components along the spline curve to complete the batch modeling of the bridge. While this method greatly reduces manpower and operation time, achieves highly automated and accurate modeling, and can quickly update the entire model, significantly improving modeling efficiency, the data processing flow is complex.

[0005] Prior art three, Chinese patent number 202411659868.2, discloses a method for calculating earthwork volume in complex terrain based on Civil 3D software, relating to the field of earthwork calculation technology. Specifically, it addresses the problem in the background technology of requiring significant time and effort for calculations while still struggling to guarantee accuracy by providing a method for calculating earthwork volume in complex terrain based on Civil 3D software. Although leveraging the powerful capabilities of Civil 3D to establish a three-dimensional digital terrain model of trenches and then calculate earthwork significantly reduces working time while ensuring calculation accuracy, its ability to handle large-scale terrain is limited.

[0006] Currently, existing technologies 1, 2, and 3 suffer from a lack of parametric modeling capabilities, complex data processing workflows, and limited ability to handle large-scale terrain. To address these issues, this invention provides a method for creating smooth, non-uniform rational B-spline 3D terrain entities through fitting. Summary of the Invention

[0007] The main objective of this invention is to provide a method and system for fitting and creating three-dimensional terrain entities using smooth, non-uniform rational B-splines, in order to solve the problems of limited parametric modeling capabilities, complex data processing procedures, and limited ability to handle large-scale terrain in the prior art.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for fitting and creating 3D terrain entities using smooth, non-uniform rational B-spline, comprising the following steps:

[0010] Based on topographic contour lines, a triangular mesh surface is constructed in a 3D civil engineering design software, and the rectangular plane boundary range required for fitting non-uniform rational B-spline terrain entities is determined. The contour lines are converted into digital elevation model data, and a control point dataset is generated and extracted through the raster surface to provide basic geometric parameters for fitting non-uniform rational B-spline surfaces.

[0011] Create the bottom plane that encloses the non-uniform rational B-spline 3D terrain entity; create the four side surfaces that enclose the non-uniform rational B-spline 3D terrain entity: use the 3D surface surface, the bottom plane, and the four side surfaces to enclose the non-uniform rational B-spline 3D terrain entity.

[0012] As a further improvement of the present invention, the process of creating a bottom plane that encloses a non-uniform rational B-spline three-dimensional terrain entity includes the following steps:

[0013] Create the bottom plane surfaced that encloses the non-uniform rational B-spline 3D terrain entity; create four control points for the bottom plane.

[0014] Obtain the minimum elevation value in the control point dataset, define the minimum thickness of a non-uniform rational B-spline 3D terrain entity, and the elevation of the bottom plane; create four control lines for the bottom plane, and the elevation values ​​of the four lines; create the bottom plane using the four control lines.

[0015] Create four lateral surfaces that enclose a non-uniform rational B-spline 3D terrain entity; use the 3D surface surfacet, the bottom plane surfaced, and the four lateral surfaces to enclose the non-uniform rational B-spline 3D terrain entity.

[0016] As a further improvement of the present invention, the process of creating four lateral surfaces that enclose and generate a non-uniform rational B-spline three-dimensional terrain entity includes the following steps:

[0017] Create four lateral surfaces to enclose a non-uniform rational B-spline 3D terrain entity; obtain the maximum elevation value in the control point dataset;

[0018] Using line1 as the extrusion object, with the normal of surface2 as the extrusion direction, and the extrusion height as the extrusion surface surface1 of line1, create the extrusion surface surface1 of line1; in the same way, create the extrusion surfaces surface2, surface3, and surface4 of line2, line3, and line4 respectively.

[0019] A non-uniform rational B-spline 3D terrain entity is formed by using a 3D surface surfacet, a bottom plane surfaced, and four side surfaces.

[0020] As a further improvement of the present invention, the process of creating four lateral surfaces that enclose and generate a non-uniform rational B-spline three-dimensional terrain entity includes the following steps:

[0021] Extract the maximum elevation value from the control point dataset, and combine it with the obtained minimum elevation value and minimum thickness to obtain the lateral stretching height;

[0022] The defined bottom plane boundary line is used as the extrusion datum; traditional normal extrusion is abandoned and an absolute vertical vector is established; based on the bottom plane coordinate system, a unit direction vector perpendicular to the XY plane is generated; with line1 as the datum line, the extrusion height is extended along the direction of the unit direction vector to generate the side surface; four side surfaces are generated iteratively in sequence.

[0023] The top, bottom, and side surfaces of the following elements are topologically integrated; through spatial position constraints, the six surfaces form a continuous closed region at the boundary, constituting a non-uniform rational B-spline three-dimensional terrain entity.

[0024] As a further improvement to the present invention, the process of forming a continuous closed region at the boundary of the six curved surfaces includes the following steps:

[0025] Extract the boundary lines of the four generated side surfaces, and simultaneously obtain the top and bottom boundaries;

[0026] Each control line of the bottom plane surfaced is positionally bound to the bottom boundary of the corresponding side surface to form a seamless connection; the four boundary lines of the surface surfacet are coordinately aligned with the top boundaries of the four side surfaces; the lateral boundaries of adjacent side surfaces are collinearly coupled to eliminate gaps.

[0027] A closed solid structure is generated. The bottom plane surfaced provides the reference coordinate system, and its four control lines become the starting point of all geometric connections. The four side surfaces extend along the absolute vertical direction, mapping the bottom boundary to the top boundary. The surface surface surfacet forms a closed interface with the top of the side surfaces through the preset boundary position. The final output is a closed non-uniform rational B-spline terrain solid directly composed of six surfaces through spatial constraints.

[0028] As a further improvement of the present invention, the top boundary is the four edge lines of the three-dimensional surface surface; the bottom boundary is the four control lines of the bottom plane surface.

[0029] As a further improvement of the present invention, the process of forming a seamless connection includes the following steps:

[0030] Extract the bottom plane control line as the reference geometric element; simultaneously obtain the bottom boundary lines of the four generated side surfaces, and record them as geometric elements;

[0031] Set the local coordinate system of the bottom plane surfaced as the global reference system; match the coordinates of each control point on the bottom boundary line of the side surface with the coordinates of the corresponding control line point by point;

[0032] After coordinate realignment, the control line completely coincides with the bottom boundary of the side, forming a rigid geometric connection.

[0033] As a further improvement of the present invention, it also includes establishing a triangular mesh surface of the original terrain of the target area based on the terrain contour lines using the surface function of civil engineering 3D design software; and determining the rectangular planar boundary of the terrain entity to be fitted into a non-uniform rational B-spline according to the actual needs of the project.

[0034] As a further improvement of the present invention, it also includes converting topographic contour data into digital elevation model data; loading the digital elevation model with specified control point spacing into civil engineering 3D design software to generate a raster surface; adjusting the display model of the raster surface to control points, extracting all control points of the raster surface, and obtaining a control point dataset.

[0035] To achieve the above objectives, the present invention also provides the following technical solution:

[0036] A system for fitting and creating 3D terrain entities using smooth, non-uniform rational B-splines includes:

[0037] The module for fitting rectangular planar boundaries is used to create a triangular mesh surface of the original terrain of the target area based on terrain contour lines using Civil 3D's surface functionality. The rectangular planar boundary to be fitted as a non-uniform rational B-spline terrain entity is determined according to actual engineering needs.

[0038] The control point dataset module is used to convert terrain contour data into DEM data; load the DEM with specified control point spacing in Civil 3D to generate a raster surface; adjust the display model of the raster surface to control points, extract all control points of the raster surface, and obtain the control point dataset;

[0039] The NURBS 3D Terrain Entity Model module is used to create the bottom plane that encloses and generates a non-uniform rational B-spline 3D terrain entity; and to create the four side surfaces that enclose and generate a non-uniform rational B-spline 3D terrain entity: the 3D surface surface, the bottom plane, and the four side surfaces are used to enclose and generate a non-uniform rational B-spline 3D terrain entity.

[0040] This invention establishes a triangular mesh surface, specifies the boundary of the terrain entity to be fitted into a non-uniform rational B-spline, converts it into DEM data, creates a raster surface, extracts raster points, fits a non-uniform rational B-spline curve along the UV direction, and fits it into a non-uniform rational B-spline terrain entity. It can quickly and efficiently achieve smooth fitting of non-uniform rational B-spline 3D terrain entities; the grid spacing of control points can be customized to adjust the surface fitting accuracy as needed; the generated non-uniform rational B-spline 3D terrain entity can be applied to CAE simulation calculations; it is suitable for combination with panel dam zoning quantity calculation algorithms, achieving rapid and refined 3D solution of panel dam zoning quantities by inputting the maximum contour of the panel dam; and it solves the problem of non-smoothness in traditional triangular mesh surface modeling. Attached Figure Description

[0041] Figure 1 This is a schematic flowchart illustrating the steps of an embodiment of the method for creating a smooth, non-uniform rational B-spline three-dimensional terrain entity by fitting and transmitting a smooth, non-uniform rational B-spline according to the present invention.

[0042] Figure 2 This is a flowchart illustrating the specific process of creating a smooth, non-uniform rational B-spline 3D terrain entity fitting method according to the present invention.

[0043] Figure 3 This is a three-dimensional schematic diagram of the fitting results of the smooth, non-uniform rational B-spline three-dimensional terrain entity based on Civil 3D in this invention.

[0044] Figure 4 This is a schematic diagram illustrating the steps of determining the rectangular planar boundary to be fitted into a non-uniform rational B-spline terrain entity, as an embodiment of the method for creating a smooth non-uniform rational B-spline three-dimensional terrain entity according to the present invention.

[0045] Figure 5 This is a triangular mesh surface diagram of the original terrain in the method for fitting and creating smooth, non-uniform rational B-spline three-dimensional terrain entities according to the present invention.

[0046] Figure 6 A flowchart illustrating the steps for obtaining a control point dataset in an embodiment of the method for creating a smooth, non-uniform rational B-spline 3D terrain entity fitting of the present invention.

[0047] Figure 7 This is a diagram showing the grid control point spacing in the method for creating a smooth, non-uniform rational B-spline 3D terrain entity fitting in this invention.

[0048] Figure 8 This is a grid surface diagram used in the method for creating a smooth, non-uniform rational B-spline three-dimensional terrain entity fitting in this invention.

[0049] Figure 9 This is a control point dataset image from the method for creating a smooth, non-uniform rational B-spline 3D terrain entity fitting in this invention.

[0050] Figure 10 This is a set of diagrams of non-uniform rational B-spline curves used in the method for creating smooth non-uniform rational B-spline three-dimensional terrain entities according to the present invention.

[0051] Figure 11 The present invention provides a method for creating a smooth, non-uniform rational B-spline three-dimensional terrain entity fitting method, which generates a non-uniform rational B-spline three-dimensional surface map.

[0052] Figure 12 This is a flowchart illustrating the steps of creating the bottom plane of a non-uniform rational B-spline three-dimensional terrain entity, as described in one embodiment of the method for fitting and creating a smooth, non-uniform rational B-spline three-dimensional terrain entity according to the present invention.

[0053] Figure 13 This is a schematic diagram of the functional modules of an embodiment of the smooth non-uniform rational B-spline three-dimensional terrain entity fitting and creation system of the present invention.

[0054] Figure 14 This is a schematic diagram of the structure of an embodiment of the electronic device of the present invention;

[0055] Figure 15 This is a schematic diagram of the structure of one embodiment of the storage medium of the present invention. Detailed Implementation

[0056] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0057] The terms "first," "second," and "third" used in this invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this invention are only used to explain the relative positional relationships and movements between components in a specific orientation (as shown in the accompanying drawings). If the specific orientation changes, the directional indications also change accordingly. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices.

[0058] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0059] like Figure 1 As shown, this embodiment provides an example of a method for fitting and creating 3D terrain entities using smooth, non-uniform rational B-splines. Specifically, this method includes the following steps:

[0060] Step S1: Based on the terrain contour lines, use Civil 3D's surface functionality to create a triangular mesh surface of the original terrain in the target area; determine the rectangular planar boundary to be fitted into a non-uniform rational B-spline terrain entity according to actual engineering needs:

[0061] Step S2: Convert the terrain contour data into DEM data; load the DEM with specified control point spacing in Civil 3D to generate a raster surface; adjust the display model of the raster surface to control points, extract all control points of the raster surface, and obtain the control point dataset;

[0062] Step S3: Create the bottom plane that encloses the non-uniform rational B-spline 3D terrain entity; create the four side surfaces that enclose the non-uniform rational B-spline 3D terrain entity: use the 3D surface surface, the bottom plane, and the four side surfaces to enclose the non-uniform rational B-spline 3D terrain entity.

[0063] Preferably, in this embodiment, based on the terrain contour lines, a triangular mesh surface of the original terrain of the target area is established using the surface function of Civil 3D; according to the actual engineering needs, the rectangular planar boundary to be fitted into a non-uniform rational B-spline terrain entity is determined, including the minimum X coordinate x. min Maximum X coordinate x max Minimum Y coordinate y min Maximum Y-coordinate max The process involves converting contour data into digital elevation model (DEM) data, using the rectangular plane boundary as the outer boundary of the terrain triangulation surface, exporting the terrain triangulation surface as a DEM, and specifying the grid control point spacing according to the required fitting accuracy of the surface. In Civil 3D, a DEM with defined control point spacing is loaded to generate a raster surface. The display model of the raster surface is adjusted to control points, and all control points of the raster surface are extracted to obtain a control point dataset Pts. Points with the same Y value in the control point dataset are grouped together, and then arranged in ascending order of X value. Each group of arranged data is fitted with a non-uniform rational B-spline curve in the U direction to obtain a set of non-uniform rational B-spline curves in the U direction. Points with the same X value in the control point dataset are grouped together, and then arranged in ascending order of X value. Each group of arranged data is fitted with a non-uniform rational B-spline curve in the V direction to obtain a set of non-uniform rational B-spline curves in the V direction. The generated sets of non-uniform rational B-spline curves in the U direction and the V direction are then fitted together to form a smooth non-uniform rational B-spline 3D surface surface_t. Create the bottom plane surface_d that encloses the non-uniform rational B-spline 3D terrain entity: Create four control points P1(x) of the bottom plane. min y min ), P2(x min y max ), P3(x max y max ), P4(x max y min Obtain the minimum elevation value Z in the control point dataset Pts; min Define the minimum thickness h of a non-uniform rational B-spline 3D terrain entity, then the elevation of the bottom plane is Z. min-hCreate four control lines for the bottom plane: line1(P1, P2), line2(P2, P3), line3(P3, P4), and line4(P4, P1). The elevation values ​​of these four lines are Z. min-h Create a bottom plane surfaced using four control lines; create four lateral surfaces to enclose and generate a non-uniform rational B-spline 3D terrain entity; obtain the maximum elevation value Z in the control point dataset Pts. max Then the stretching height h of the four side surfaces cm For Z max -Z min+h Using line1 as the object to be stretched, and the normal of surface2 as the stretching direction, with h as the stretching direction. cm Create an extruded surface surface (surface1) for line1 to extend the height; similarly, create extruded surfaces surface2, surface3, and surface4 for lines2, 3, and 4 respectively; use the 3D surface surface (surfacet), the bottom plane (surfaced), and the four side surfaces (surface1, surface2, surface3, and surface4) to form a non-uniform rational B-spline 3D terrain entity. This involves creating a triangular mesh surface, specifying the boundaries to be fitted into a non-uniform rational B-spline terrain entity, converting to DEM data, creating a raster surface, extracting raster points, fitting a non-uniform rational B-spline curve along the UV direction, and fitting the non-uniform rational B-spline terrain entity (see appendix for details). Figure 2 and appendix Figure 3 ).

[0064] Furthermore, such as Figure 4 As shown, the process of determining the rectangular planar boundary of the terrain entity to be fitted into a non-uniform rational B-spline in step S1 specifically includes the following steps:

[0065] Step S11: Obtain project data such as contour lines and elevation points; add contour data to the surface definition to generate a triangular mesh surface; check and adjust the surface smoothness, delete triangles, and eliminate artifacts through the local smoothing function; divide the area according to the project requirements, reconstruct the surface boundary, and regenerate the optimized triangular mesh surface.

[0066] Step S12: Obtain the closed curve of the target area, extract the outer contour line from the topographic map as the boundary line; after generating the triangular mesh surface, hide other contour data and retain the outer closed curve; select the optimized triangular mesh surface and convert it into a 3D solid model.

[0067] Step S13: Unify the format of the generated triangular mesh surface and 3D solid model, select the terrain range, and generate an initial non-uniform rational B-spline surface; then discretize the initial non-uniform rational B-spline surface, uniformly extract the contour lines, fit the initial non-uniform rational B-spline surface after discretization, and adjust the flexibility parameter to control the smoothness.

[0068] Preferably, in this embodiment, contour lines and elevation points are acquired and added to the surface definition to generate a triangular mesh surface. By constructing a triangular mesh from scattered elevation point data, the irregularity of the terrain data can be effectively handled, generating a continuous surface model. After generating the triangular mesh surface, the surface smoothness needs to be checked and adjusted, unnecessary triangles are deleted, and artifacts are eliminated through local smoothing. This ensures the smoothness and continuity of the final surface, avoiding visual or functional defects caused by data noise or model irregularities. The generated triangular mesh surface and solid are exported to a unified format, and the terrain range is selected to generate an initial non-uniform rational B-spline surface. After generating the initial non-uniform rational B-spline surface, it is discretized, contour lines are uniformly extracted, and the initial non-uniform rational B-spline surface is fitted. The outer contour lines in the terrain map are extracted as boundary lines, and other contour data are hidden after generating the triangular mesh surface, retaining the outer closed curves. Subsequently, the optimized triangular mesh surface is converted into a three-dimensional solid model. By generating elevation data and triangulation networks, and then fitting non-uniform rational B-spline surfaces, high-precision 3D terrain models can be generated, suitable for engineering design, terrain analysis, and landscape planning. The generation and optimization process of non-uniform rational B-spline surfaces is highly efficient, capable of quickly processing complex terrain data and reducing computation time and resource consumption. Non-uniform rational B-spline surfaces offer good flexibility and modifiability, allowing users to adjust the shape and parameters of the surface according to engineering needs, meeting the requirements of different application scenarios. The generated non-uniform rational B-spline surfaces can be used for terrain analysis, landscape design, and water conservancy projects, providing intuitive 3D visualization effects, facilitating decision-making and planning (see appendix for details). Figure 5 ).

[0069] Furthermore, such as Figure 6 As shown, the process of obtaining the control point dataset in step S2 specifically includes the following steps:

[0070] Step S21: Convert the terrain contour data into DEM data; use the rectangular plane boundary as the outer boundary of the terrain triangular mesh surface; export the terrain triangular mesh surface as a DEM, and specify the grid control point spacing according to the required fitting accuracy of the surface.

[0071] Step S22: Load the DEM with specified control point spacing in Civil 3D to generate a raster surface; adjust the display model of the raster surface to control points, extract all control points of the raster surface, and obtain the control point dataset;

[0072] Step S23: Analyze the control point dataset to obtain a set of non-uniform rational B-spline curves in the U direction and a set of non-uniform rational B-spline curves in the V direction; fit the generated set of non-uniform rational B-spline curves in the U direction and the set of non-uniform rational B-spline curves in the V direction into a smooth non-uniform rational B-spline three-dimensional surface.

[0073] Preferably, this embodiment achieves digital simulation of terrain by converting contour data into regular two-dimensional grid data (DEM). After generating the DEM, the spacing of the grid control points is specified according to the fitting accuracy requirements; the setting of the control point spacing directly affects the smoothness and accuracy of the final non-uniform rational B-spline surface; the display model of the DEM grid surface is adjusted to the control points, and after extracting all control points, non-uniform rational B-spline curve sets in the U and V directions are fitted, finally constructing a smooth non-uniform rational B-spline three-dimensional surface. Through the generation of the DEM and the precise setting of control points, high-precision modeling of terrain can be achieved, meeting the application needs of engineering design, terrain analysis, and other fields. The generation of non-uniform rational B-spline surfaces makes the terrain model smoother and more continuous, facilitating visualization and interactive operation in a three-dimensional environment. The mathematical expression of non-uniform rational B-spline surfaces makes the processing and rendering of terrain data more efficient, especially suitable for processing large-scale terrain data (see Appendix for specific principles). Figure 7 Appendix Figure 8 Appendix Figure 9 and appendix Figure 10 ).

[0074] Furthermore, the process of specifying the grid control point spacing in step S21 specifically includes the following steps:

[0075] Step S211: Convert the terrain contour data into DEM data; use the rectangular plane boundary as the outer boundary of the terrain triangular mesh surface; export the terrain triangular mesh surface as a DEM; load the contour data and select all contour lines;

[0076] Step S212: Group all selected contour lines, call the surface generation tool, and generate a triangular mesh surface using the contour line group as the data source; select the outer closed curve, and set the predefined rectangular plane boundary line in the graphical interface as the outer boundary;

[0077] Step S213: Set the boundary type parameters, perform surface regeneration, enable the rectangular boundary and trim the triangular mesh to the boundary range, adjust the surface display style, and verify whether the outer boundary accurately limits the surface range.

[0078] Preferably, this embodiment converts contour data into DEM data, enabling a numerical representation of the terrain and facilitating subsequent terrain analysis and modeling. When generating the terrain triangular mesh surface, using the rectangular planar boundary as the external boundary ensures that the generated surface is clipped within a specified area, preventing it from exceeding the set range. By calling the surface generation tool and using contour groups as the data source to generate the terrain triangular mesh surface, three-dimensional terrain modeling can be achieved. By setting the boundary type parameters and performing a regeneration operation, the rectangular boundary is ensured to be effective, and the triangular mesh is clipped within the boundary range. After generating the surface, adjusting its display style optimizes the visual effect, allowing users to intuitively view and analyze the terrain data.

[0079] Furthermore, the process of extracting all control points of the raster surface in step 22 specifically includes the following steps:

[0080] Step S221: Load the DEM data with specified control point spacing in Civil 3D to generate a raster surface; right-click on the surface node in the tool space to create a new surface, enter a name, and add the DEM data to the surface definition;

[0081] Step S222: Change the display model of the raster surface from the default triangular mesh or contour lines to control points; use Civil 3D's extraction tool to select all control points of the raster surface; the extraction results generate a control point dataset containing coordinates.

[0082] Preferably, in this embodiment, a raster surface can be generated by loading DEM data with specified control point spacing. This surface is used to represent the three-dimensional geometric model of the terrain. A new surface object is created in the toolspace, and the DEM data is added to the surface definition, giving the surface terrain information. The display model of the raster surface is changed from the default triangular mesh or contour lines to control points. Using Civil 3D's extraction tool, all control points of the raster surface can be selected, and a control point dataset containing coordinates can be generated. This function is crucial for subsequent tasks such as terrain analysis and earthwork calculation.

[0083] Furthermore, the process of analyzing the control point dataset in step S23 specifically includes the following steps:

[0084] Step S231: Group the points with the same Y value in the control point dataset into one group, and then arrange them in order of increasing X value. Fit each group of data into a non-uniform rational B-spline curve in the U direction to obtain a set of non-uniform rational B-spline curves in the U direction.

[0085] Step S232: Group the points with the same X value in the control point dataset into one group, and then arrange them in order of X value from smallest to largest. Fit the data of each group into a non-uniform rational B-spline curve in the V direction to obtain a group of non-uniform rational B-spline curves in the V direction.

[0086] Step S233: Fit the generated set of non-uniform rational B-spline curves in the U direction and the set of non-uniform rational B-spline curves in the V direction into a smooth non-uniform rational B-spline three-dimensional surface.

[0087] Preferably, points with the same Y value in the control point dataset are grouped together and arranged in ascending order of X value; points with the same X value are grouped together and arranged in ascending order of Y value; non-uniform rational B-spline curves are fitted to the grouped data in the U and V directions respectively; the generated non-uniform rational B-spline curves in the U and V directions are combined to fit a smooth 3D non-uniform rational B-spline surface. Non-uniform rational B-spline technology can accurately represent complex surfaces such as terrain, reduce data redundancy, and improve modeling accuracy; the shape of the non-uniform rational B-spline surface can be easily modified by adjusting control points, facilitating subsequent optimization and adjustment; grouping and sorting simplify the data processing flow and improve modeling efficiency; the generated non-uniform rational B-spline surface can be used for 3D visualization and geological analysis, providing support for engineering design and decision-making (see appendix for specific principles). Figure 11 ).

[0088] Furthermore, such as Figure 12 As shown, the process of creating the bottom plane of the enclosed non-uniform rational B-spline 3D terrain entity in step S3 specifically includes the following steps:

[0089] Step S31: Create the bottom plane surfaced that encloses the non-uniform rational B-spline 3D terrain entity; create four control points P1 on the bottom plane;

[0090] Among them, four control points P1(x min y min ), P2(x min y max ), P3(x max y max ), P4(x max y min );

[0091] Step S32: Obtain the control point dataset Pts The minimum elevation value Z in min Define the minimum thickness h of a non-uniform rational B-spline 3D terrain entity, then the elevation of the bottom plane is Z. min-h Create four control lines for the bottom plane, with elevation values ​​of 10 ... min-h Create the bottom plane using four control lines;

[0092] Among them, the four control lines of the bottom plane are line1(P1, P2), line2(P2, P3), line3(P3, P4) and line4(P4, P1);

[0093] Step S33: Create four side surfaces to enclose and generate a non-uniform rational B-spline 3D terrain entity; use the 3D surface surfacet, the bottom plane surfaced, and the four side surfaces to enclose and generate a non-uniform rational B-spline 3D terrain entity.

[0094] Preferably, in this embodiment, the bottom plane is created by defining four control points (P1, P2, P3, P4), and the minimum elevation value Z in the control point dataset is used as the basis for the bottom plane. min The elevation (Z) of the bottom plane is determined by the predefined minimum thickness h. min-h Four control lines are created based on the four control points, and the elevation values ​​of these lines are all Z. min-h Then, these four control lines are used to create the bottom plane; the three-dimensional surface surface, the bottom plane surface, and the four side surfaces are used to form a non-uniform rational B-spline three-dimensional terrain entity; by precisely controlling the elevation and shape of the bottom plane, the accuracy of the non-uniform rational B-spline three-dimensional terrain entity is ensured; using the non-uniform rational B-spline surface modeling method, the details of the terrain model can be flexibly adjusted to adapt to complex geological structures; by defining control points and control lines, the construction process of the terrain model is simplified and the modeling efficiency is improved.

[0095] Furthermore, the process of creating the four lateral surfaces of the enclosed non-uniform rational B-spline 3D terrain entity in step S33 specifically includes the following steps:

[0096] Step S331: Create the four lateral surfaces of the enclosed non-uniform rational B-spline 3D terrain entity; obtain the maximum elevation value Z in the control point dataset Pts. max Then the stretching height h of the four side surfaces cm For Z max -Z min+h ;

[0097] Step S332: Using line1 as the object to be stretched, and the normal of surface2 as the stretching direction, with h as the stretching direction. cmCreate an extruded surface surface1 for line1 to extend the height; in the same way, create extruded surfaces surface2, surface3, and surface4 for line2, line3, and line4 respectively.

[0098] Step S333: Use the three-dimensional surface surfacet, the bottom plane surfaced, and the four side surfaces to form a non-uniform rational B-spline three-dimensional terrain entity.

[0099] Preferably, this embodiment demonstrates the advantages of non-uniform rational B-splines in complex surface modeling by creating four side surfaces and extruding them to generate a three-dimensional solid; the maximum elevation value Z is obtained through the control point dataset Pts. max And calculate the stretching height h accordingly. cm This demonstrates the ability to accurately model terrain data. Using line1 as the extrusion object, it is stretched along the normal direction of surface2 to form surface1. Other side surfaces are then generated using a similar method. Finally, the 3D surface surface, bottom plane, and four side surfaces are used to enclose a non-uniform rational B-spline 3D terrain entity. The entire process, from contour line import, TIN model generation, data transformation, control point extraction, and non-uniform rational B-spline surface fitting, simplifies and simplifies terrain modeling. Non-uniform rational B-spline modeling not only accurately represents the terrain but also maintains geometric consistency in subsequent analysis, avoiding calculation deviations caused by geometric errors in traditional FEA.

[0100] Furthermore, the process of creating the four lateral surfaces of the enclosed non-uniform rational B-spline 3D terrain entity in step S331 specifically includes the following steps:

[0101] Step S33311: Extract the maximum elevation value from the control point dataset, and combine it with the obtained minimum elevation value and minimum thickness to obtain the lateral stretching height;

[0102] Step S33312: Call the defined bottom plane boundary line as the extrusion datum; abandon the traditional normal extrusion and establish an absolute vertical vector; based on the bottom plane coordinate system, generate a unit direction vector perpendicular to the XY plane; using line1 as the datum line, extend the extrusion height along the direction of the unit direction vector to generate the side surface; iterate to generate four side surfaces in sequence.

[0103] Step S33313: Perform topological integration on the top, bottom and side surfaces of the following elements; through spatial position constraints, make the six surfaces form a continuous closed region at the boundary, thus forming a non-uniform rational B-spline three-dimensional terrain entity.

[0104] Preferably, this embodiment employs a complete technical process for generating four side surfaces of a non-uniform rational B-spline 3D terrain entity through integration and enclosure. Based on a dynamic calculation model of maximum / minimum elevation values ​​and minimum thickness, a height-adaptive side stretching parameter system is constructed to ensure the terrain entity has precise geometric tolerance in the Z-axis direction. Standardization of the absolute vertical vector eliminates surface distortion caused by traditional normal stretching, ensuring the side surfaces strictly adhere to the Z-axis direction of the world coordinate system. The bottom plane boundary line is used as the reference geometric element, and parameterized surface generation is established through the mathematical definition of the unit direction vector. Strict geometric consistency is ensured for the four side surfaces, with the UV parameterized direction of each surface maintaining a topological correspondence with the bottom boundary, providing a standardized geometric basis for subsequent Boolean operations. Spatial position constraint algorithms control the boundary continuity of the six surfaces (top / bottom / four side surfaces), and the G1 continuity condition of the non-uniform rational B-spline surface ensures parameterized connection between adjacent surfaces. The topology integration process uses the BREP data structure, ensuring the final generated closed entity meets strict manifold geometric requirements and possesses complete boundary representation characteristics. The entire process forms a complete parametric construction chain from 2D boundaries to 3D entities. All geometric elements maintain the mathematical properties of non-uniform rational B-splines, supporting subsequent precision adjustments and parametric modifications. The generated entities possess precise geometric definitions and can be directly used in professional engineering applications such as finite element analysis and terrain visualization. Ultimately, it achieves the automated generation of parametric 3D terrain entities from discrete elevation data. Its core value lies in integrating geometric constraints, topological relationships, and parametric control in the terrain modeling process into a unified mathematical expression system.

[0105] Furthermore, the process of forming a continuous closed region at the boundary of the six surfaces in step S33313 specifically includes the following steps:

[0106] Step S333131: Extract the boundary lines of the four generated side surfaces, and simultaneously obtain the top and bottom boundaries;

[0107] The top boundary is defined by the four edge lines of the three-dimensional surface surface; the bottom boundary is defined by the four control lines of the bottom plane surface.

[0108] Step S333132: Bind each control line of the bottom plane surfaced to the bottom boundary of the corresponding side surface to form a seamless connection; align the four boundary lines of the surface surfacet with the top boundaries of the four side surfaces; and collinearly couple the lateral boundaries of adjacent side surfaces to eliminate gaps.

[0109] Step S333133: Generate a closed solid structure. The bottom plane surfaced provides the reference coordinate system, and its four control lines become the starting point of all geometric connections. The four side surfaces extend along the absolute vertical direction, mapping the bottom boundary to the top boundary. The surface surface surfacet forms a closed interface with the top of the side surfaces through the preset boundary position. The final output is a closed non-uniform rational B-spline terrain solid directly composed of six surfaces through spatial constraints.

[0110] Preferably, this embodiment employs a technical process for fusing the boundaries of six curved surfaces to form a closed non-uniform rational B-spline terrain entity. Based on the reference coordinate system of the bottom plane control line, a vertical mapping relationship is established from the bottom surface to the top surface, achieving parametric alignment between the side surfaces and the top / bottom surfaces. By binding the boundary line positions and synchronizing the coordinates, geometric discontinuities between surfaces are eliminated, ensuring strict matching of the edges of each surface and forming a seamless closed-loop structure. A hierarchical constraint logic of the bottom control line, side boundaries, and top surface boundaries is used to integrate discrete surfaces into a unified topological entity. The bottom control line serves as a geometric reference, driving the vertical extension of the side surfaces. The top surface boundary is coupled to the top of the side surfaces through a preset position, forming a bidirectional constraint network, ensuring that the six surfaces satisfy the G1 continuity condition in three-dimensional space. Through boundary mapping in the vertical direction, the parametric characteristics of the bottom plane are transferred to the top surface, maintaining the mathematical consistency of the non-uniform rational B-spline surface. Collinear coupling processing of adjacent side surfaces ensures parametric connection of the lateral boundaries, ultimately generating a closed BREP structure with a complete parameter chain.

[0111] In summary, this embodiment achieves automated construction from discrete boundaries to closed entities. All surfaces are directly related through spatial constraints, eliminating the need for intermediate geometric repairs. The output non-uniform rational B-spline terrain entity meets strict manifold requirements and can directly support downstream applications such as engineering analysis and numerical simulation. Its boundary topological integrity provides a structured foundation for subsequent Boolean operations or LOD simplification. Unifying multi-source surfaces into parametric closed entities solves the accuracy loss and topological errors caused by manual stitching in traditional methods.

[0112] Furthermore, the process of forming a seamless connection in step S3331321 specifically includes the following steps:

[0113] Step S33313211: Extract the bottom plane control line as the reference geometric element; simultaneously obtain the bottom boundary lines of the four generated side surfaces, and record them as geometric elements;

[0114] Step S33313212: Set the local coordinate system of the bottom plane surfaced as the global reference system; match the coordinates of each control point on the bottom boundary line of the side surface with the coordinates of the corresponding control line point by point;

[0115] Step S33313213: After coordinate realignment, the control line completely coincides with the bottom boundary of the side, forming a rigid geometric connection.

[0116] Preferably, this embodiment uses the bottom plane control line as the reference geometric element to establish a precise matching framework in the global coordinate system. By aligning the control points of the bottom boundary line of the side surface with the bottom control line point by point, strict spatial synchronization of the parameterized geometric elements is achieved, ensuring the mathematical continuity of the connection parts. Through the unified transformation from the local coordinate system to the global reference system, the coordinate system differences of multi-source geometries are eliminated. The point-by-point matching process of the control points is essentially a synchronous optimization of the non-uniform rational B-spline parameter space, making the bottom control line and the side boundary completely coincide at the topological and geometric levels, forming a rigid connection without redundant errors. The connected body generated after coordinate realignment has structural invariance, and its mathematical expression satisfies the continuity and differentiability requirements in differential geometry. This mechanism provides a high-precision benchmark for subsequent top surface fusion and lateral coupling through bottom-level parameter synchronization, ensuring that the final entity conforms to the strict closure conditions of the BREP model.

[0117] like Figure 13 As shown, this embodiment also provides a smooth, non-uniform rational B-spline 3D terrain entity fitting and creation system. In this embodiment, the smooth, non-uniform rational B-spline 3D terrain entity fitting and creation system is applied to the smooth, non-uniform rational B-spline 3D terrain entity fitting and creation method as described in the above embodiments. The smooth, non-uniform rational B-spline 3D terrain entity fitting and creation system includes:

[0118] The module 1 for fitting rectangular planar boundaries is used to create a triangular mesh surface of the original terrain of the target area based on the terrain contour lines using Civil 3D's surface functionality; the rectangular planar boundary to be fitted into a non-uniform rational B-spline terrain entity is determined according to actual engineering needs:

[0119] Control point dataset module 2 is used to convert terrain contour data into DEM data; load the DEM with specified control point spacing in Civil 3D to generate a raster surface; adjust the display model of the raster surface to control points, extract all control points of the raster surface, and obtain the control point dataset;

[0120] NURBS 3D Terrain Entity Model Module 3 is used to create the bottom plane that encloses and generates a non-uniform rational B-spline 3D terrain entity; and to create the four side surfaces that enclose and generate a non-uniform rational B-spline 3D terrain entity: the 3D surface surface, the bottom plane, and the four side surfaces are used to enclose and generate a non-uniform rational B-spline 3D terrain entity.

[0121] Preferably, this embodiment utilizes Civil 3D's surface functionality to convert terrain contour data into triangular mesh surfaces and determines the rectangular boundaries of the non-uniform rational B-spline terrain entity based on engineering requirements. The contour data is converted into a DEM (Digital Elevation Model), and a raster surface is generated, extracting the control point dataset. By setting the control point spacing, refined processing of the terrain data is achieved, thereby improving the accuracy and continuity of the non-uniform rational B-spline surface fitting. A non-uniform rational B-spline 3D terrain entity is generated by enclosing the bottom plane and four side surfaces. Leveraging the mathematical advantages of non-uniform rational B-spline surfaces, high-precision terrain modeling and visualization are achieved. Non-uniform rational B-spline surfaces have significant advantages in reverse engineering and CAD modeling, enabling high-quality surface fitting and reconstruction.

[0122] like Figure 14 As shown, this embodiment provides an embodiment of an electronic device 4, which includes a processor 41 and a memory 42 coupled to the processor 41.

[0123] The memory 42 stores program instructions for a layout method for implementing the smooth non-uniform rational B-spline three-dimensional terrain entity fitting creation method of any of the above embodiments.

[0124] The processor 41 is used to execute program instructions stored in the memory 42 to lay out a method for fitting smooth, non-uniform rational B-spline three-dimensional terrain entities.

[0125] The processor 41 can also be referred to as a CPU (Central Processing Unit). The processor 41 may be an integrated circuit chip with signal processing capabilities. The processor 41 can also be a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components. A general-purpose processor can be a microprocessor or any conventional processor.

[0126] Furthermore, Figure 15This is a schematic diagram of the structure of a storage medium according to an embodiment of this application. The storage medium 5 of this embodiment stores program instructions 51 capable of implementing all the methods described above. These program instructions 51 can be stored in the storage medium in the form of a software product, including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) or processor to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks, or terminal devices such as computers, servers, mobile phones, and tablets.

[0127] In the several embodiments provided by this invention, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between apparatuses or units through some interfaces, and may be electrical, mechanical, or other forms.

[0128] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated units described above can be implemented in hardware or as software functional units. The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

[0129] The specific embodiments of the invention have been described in detail above, but these are merely examples, and the invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications or substitutions to the invention are also within the scope of this invention. Therefore, all equivalent transformations, modifications, and improvements made without departing from the spirit and principles of this invention should be included within the scope of this invention.

Claims

1. A method for fitting and creating 3D terrain entities using smooth, non-uniform rational B-splines, characterized in that, The process of creating a smooth, non-uniform rational B-spline 3D terrain entity fitting method includes the following steps: Based on topographic contour lines, a triangular mesh surface is constructed in a 3D civil engineering design software, and the rectangular plane boundary range required for fitting non-uniform rational B-spline terrain entities is determined. The contour lines are converted into digital elevation model data, and a control point dataset is generated and extracted through the raster surface to provide basic geometric parameters for fitting non-uniform rational B-spline surfaces. Create a bottom plane that encloses and generates a non-uniform rational B-spline 3D terrain entity; create four side surfaces that enclose and generate a non-uniform rational B-spline 3D terrain entity: use the 3D surface surface, the bottom plane, and the four side surfaces to enclose and generate a non-uniform rational B-spline 3D terrain entity; extract the maximum elevation value from the control point dataset, and combine it with the obtained minimum elevation value and minimum thickness to obtain the side stretching height; The defined bottom plane boundary line is used as the extrusion datum; traditional normal extrusion is abandoned and an absolute vertical vector is established; based on the bottom plane coordinate system, a unit direction vector perpendicular to the XY plane is generated; with line1 as the datum line, the extrusion height is extended along the direction of the unit direction vector to generate the side surface; four side surfaces are generated iteratively in sequence. Perform topological integration on the top, bottom, and side surfaces of the following elements; through spatial position constraints, make the six surfaces form a continuous closed region at the boundary, extract the boundary lines of the four generated side surface surfaces, and simultaneously obtain the top and bottom surface boundaries; Each control line of the bottom plane surfaced is positionally bound to the bottom boundary of the corresponding side surface to form a seamless connection; the four boundary lines of the surface surfacet are coordinately aligned with the top boundaries of the four side surfaces; the lateral boundaries of adjacent side surfaces are collinearly coupled to eliminate gaps; a closed solid structure is generated, with the bottom plane surfaced providing the reference coordinate system and its four control lines becoming the starting point for all geometric connections; the four side surfaces extend along the absolute vertical direction, mapping the bottom boundary to the top boundary; the surface surfacet forms a closed interface with the top of the side surfaces through preset boundary positions; the final output is a closed non-uniform rational B-spline terrain solid directly composed of six surfaces through spatial constraints; thus forming a non-uniform rational B-spline 3D terrain solid. The topographic contour data is converted into digital elevation model data; the digital elevation model with specified control point spacing is loaded into the civil engineering 3D design software to generate a raster surface; the display model of the raster surface is adjusted to control points, and all control points of the raster surface are extracted to obtain a control point dataset.

2. The method for creating a smooth, non-uniform rational B-spline three-dimensional terrain entity according to claim 1, characterized in that, The process of creating the bottom plane that encloses a non-uniform rational B-spline 3D terrain entity includes the following steps: Create the bottom plane surfaced that encloses the non-uniform rational B-spline 3D terrain entity; create four control points for the bottom plane. Obtain the minimum elevation value in the control point dataset, define the minimum thickness of a non-uniform rational B-spline 3D terrain entity, and the elevation of the bottom plane; create four control lines for the bottom plane, and the elevation values ​​of the four lines; create the bottom plane using the four control lines. Create four lateral surfaces that enclose a non-uniform rational B-spline 3D terrain entity; use the 3D surface surfacet, the bottom plane surfaced, and the four lateral surfaces to enclose the non-uniform rational B-spline 3D terrain entity.

3. The method for creating a smooth, non-uniform rational B-spline three-dimensional terrain entity according to claim 2, characterized in that, The process of creating the four lateral surfaces of a non-uniform rational B-spline 3D terrain entity includes the following steps: Create four lateral surfaces to enclose a non-uniform rational B-spline 3D terrain entity; obtain the maximum elevation value in the control point dataset; Using line1 as the extrusion object, with the normal of surface2 as the extrusion direction, and the extrusion height as the extrusion surface surface1 of line1, create the extrusion surface surface1 of line1; in the same way, create the extrusion surfaces surface2, surface3, and surface4 of line2, line3, and line4 respectively. A non-uniform rational B-spline 3D terrain entity is formed by using a 3D surface surfacet, a bottom plane surfaced, and four side surfaces.

4. The method for creating a smooth, non-uniform rational B-spline three-dimensional terrain entity according to claim 1, characterized in that, The top boundary is defined by the four edge lines of the three-dimensional surface surface; the bottom boundary is defined by the four control lines of the bottom plane surface.

5. The method for creating a smooth, non-uniform rational B-spline three-dimensional terrain entity according to claim 1, characterized in that, The process of creating a seamless connection includes the following steps: Extract the bottom plane control line as the reference geometric element; simultaneously obtain the bottom boundary lines of the four generated side surfaces, and record them as geometric elements; Set the local coordinate system of the bottom plane surfaced as the global reference system; match the coordinates of each control point on the bottom boundary line of the side surface with the coordinates of the corresponding control line point by point; After coordinate realignment, the control line completely coincides with the bottom boundary of the side, forming a rigid geometric connection.

6. The method for creating a smooth, non-uniform rational B-spline three-dimensional terrain entity according to claim 1, characterized in that, It also includes establishing the triangular mesh surface of the original terrain of the target area based on the terrain contour lines and using the surface function of civil engineering 3D design software; and determining the rectangular planar boundary to be fitted into a non-uniform rational B-spline terrain entity according to the actual needs of the project.

7. A system for fitting and creating smooth, non-uniform rational B-spline three-dimensional terrain entities, applied to the method for fitting and creating smooth, non-uniform rational B-spline three-dimensional terrain entities as described in any one of claims 1 to 6, characterized in that, The smooth, non-uniform rational B-spline 3D terrain entity fitting and creation system includes: The module for fitting rectangular planar boundaries is used to create a triangular mesh surface of the original terrain of a target area based on topographic contour lines using the surface function of 3D civil engineering design software. It determines the rectangular planar boundary to be fitted into a non-uniform rational B-spline terrain entity according to actual engineering needs. The control point dataset module is used to convert topographic contour data into digital elevation model data; load the digital elevation model with specified control point spacing into the civil engineering 3D design software to generate a raster surface; adjust the display model of the raster surface to control points, extract all control points of the raster surface, and obtain the control point dataset. The NURBS 3D Terrain Entity Model module is used to create the bottom plane that encloses and generates a non-uniform rational B-spline 3D terrain entity; and to create the four side surfaces that enclose and generate a non-uniform rational B-spline 3D terrain entity: the 3D surface surface, the bottom plane, and the four side surfaces are used to enclose and generate a non-uniform rational B-spline 3D terrain entity.

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