An internet-based digital city model display method and system

Abstract

The application discloses an Internet-based digital city model display method and system, and relates to the technical field of data processing.The method comprises the following steps: acquiring the spatial position coordinates and network transmission rate parameters of a target event; taking the spatial position coordinates as a reference point, dividing a three-dimensional city scene into a core attention area and a secondary buffer area; calculating the upper limit value of the polygon number of a three-dimensional model allowed to be loaded according to the transmission rate parameters; based on the range of the divided area and the upper limit value of the polygon number, performing asymmetric distribution on the upper limit value of the polygon number according to the preset business priority of the city model of different semantic types, generating and sending a dynamic acquisition request, and receiving returned target model data flow; and analyzing the target model data flow and performing a differential rendering display strategy according to the semantic type. The application dynamically adapts to the network environment and preferentially allocates rendering resources according to the priority, and the display efficiency of key city models is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of data processing technology, and specifically to a method and system for displaying digital city models based on the Internet. Background Technology

[0002] With the continuous advancement of digital twin and smart city construction, internet-based digital city model visualization has become an important tool for urban management and emergency command. The data scale of various 3D city scenes is constantly expanding, allowing users to view the spatial environment surrounding target events through terminal devices. As a crucial tool for decision support, the efficient loading and clear display of 3D city models significantly impact the effectiveness of event analysis.

[0003] Currently, the display methods for digital city models mainly rely on dynamic loading technology based on viewpoint distance (LOD). By calculating the geometric distance between the viewpoint and each city model in real time, loading strategies for models with different levels of detail are determined to control the rendering overhead of the overall scene.

[0004] However, relying solely on viewpoint distance for indiscriminate model loading makes it difficult to adapt to the dynamic changes in the internet transmission environment and the differences in the primary and secondary importance of different types of facilities in the target event. This results in a massive amount of data transmission occurring instantly, causing network congestion and reducing the display efficiency of key city models. Summary of the Invention

[0005] To address the aforementioned shortcomings, a method and system for displaying digital city models based on the Internet is provided.

[0006] In a first aspect, the present invention provides a method for displaying a digital city model based on the Internet, characterized in that the method includes:

[0007] Obtain the spatial coordinates of the target event and the current internet connection's transmission rate parameters;

[0008] Using the aforementioned spatial coordinates as a reference point, the 3D city scene to be displayed is divided into a core focus area and a secondary buffer area.

[0009] Based on the transmission rate parameter, calculate the upper limit of the number of polygons of the 3D model that can be loaded within the current rendering cycle;

[0010] Based on the range of the core focus area and the secondary buffer area, and the upper limit of the number of polygons, the upper limit of the number of polygons is asymmetrically allocated according to the preset business priority of the city model of different semantic types in the 3D city scene to be displayed, and a dynamic acquisition request is generated.

[0011] The dynamic acquisition request is sent to the server via the Internet, and the target model data stream returned by the server based on the dynamic acquisition request is received.

[0012] The target model data stream is parsed, and a differentiated rendering and display strategy is executed in the 3D city scene to be displayed, based on the semantic type corresponding to the target model data stream.

[0013] By employing the aforementioned technical solution, the spatial coordinates of the target event and the transmission rate parameters of the current internet connection are obtained, clarifying the physical center of the event and the network's carrying capacity. Using the spatial coordinates as a reference point, the 3D city scene to be displayed is divided into a core focus area and a secondary buffer area, distinguishing the spatial hierarchy of the scene. Based on the transmission rate parameters, the upper limit of the number of polygons allowed to be loaded in the current rendering cycle is calculated, quantifying network transmission capacity into a specific model face limit to avoid data requests exceeding network load and causing congestion. Based on the range of the core focus area and the secondary buffer area, and the upper limit of the number of polygons, the upper limit of the number of polygons is asymmetrically allocated according to the preset business priorities of city models of different semantic types in the 3D city scene, and dynamic acquisition requests are generated. This ensures that important areas and high-priority semantic types of models receive more polygon allocation quotas under limited network conditions. The dynamic acquisition requests are sent and received via the internet, reducing the network transmission of invalid data. The target model data stream is parsed, and differentiated rendering and display strategies are executed in the 3D city scene according to the semantic type corresponding to the target model data stream, allowing models of different semantic types to present different visual details, thereby improving the display efficiency of key city models.

[0014] Secondly, the present invention provides an Internet-based digital city model display system, the system comprising:

[0015] The acquisition module is used to acquire the spatial coordinates of the target event and the transmission rate parameters of the current Internet connection;

[0016] The partitioning module is used to divide the 3D city scene to be displayed into a core focus area and a secondary buffer area, based on the spatial location coordinates.

[0017] The calculation module is used to calculate the upper limit of the number of polygons of the 3D model that can be loaded within the current rendering cycle based on the transmission rate parameter.

[0018] The allocation module is used to asymmetrically allocate the upper limit of the number of polygons based on the range of the core focus area and the secondary buffer area, as well as the upper limit of the number of polygons, according to the preset business priority of the city model of different semantic types in the 3D city scene to be displayed, and generate dynamic acquisition requests.

[0019] The transceiver module is used to send the dynamic acquisition request to the server via the Internet and to receive the target model data stream returned by the server according to the dynamic acquisition request.

[0020] The rendering module is used to parse the target model data stream and execute differentiated rendering and display strategies in the 3D city scene to be displayed, based on the semantic type corresponding to the target model data stream. Attached Figure Description

[0021] Figure 1 A flowchart illustrating an internet-based digital city model display method provided in an embodiment of the present invention;

[0022] Figure 2 This is a schematic diagram illustrating the division of a core area of ​​interest and a secondary buffer area according to an embodiment of the present invention.

[0023] Figure 3 A flowchart illustrating a differentiated rendering and display strategy provided in an embodiment of the present invention.

[0024] Figure 4 This is a schematic diagram of the architecture of an Internet-based digital city model display system provided in an embodiment of the present invention. Detailed Implementation

[0025] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0026] Example 1

[0027] like Figure 1 As shown, a method for displaying a digital city model based on the Internet includes:

[0028] Obtain the spatial coordinates of the target event and the current internet connection's transmission rate parameters;

[0029] Using spatial coordinates as a reference point, the 3D city scene to be displayed is divided into a core focus area and a secondary buffer area;

[0030] Based on the transmission rate parameter, calculate the upper limit of the number of polygons of the 3D model that can be loaded within the current rendering cycle;

[0031] Based on the scope of the core focus area and the secondary buffer area, as well as the upper limit of the number of polygons, the upper limit of the number of polygons is asymmetrically allocated according to the business priority preset for different semantic types of city models in the 3D city scene to be displayed, and dynamic acquisition requests are generated.

[0032] The dynamic acquisition request is sent to the server via the Internet, and the target model data stream returned by the server based on the dynamic acquisition request is received.

[0033] The target model data stream is parsed, and a differentiated rendering and display strategy is executed in the 3D city scene to be displayed, based on the semantic type corresponding to the target model data stream.

[0034] By obtaining the spatial coordinates of the target event and the transmission rate parameters of the current internet connection, the physical center of the event and the network capacity are determined. When obtaining the spatial coordinates of the target event, the target event includes, but is not limited to, urban management events requiring emergency response, such as sudden urban fires, traffic accidents, and medical emergencies. The event location can be manually marked by the user in the 3D city scene, or the geographical coordinates of the corresponding location can be automatically obtained by accessing an external event reporting system. For example, the obtained spatial coordinates are longitude 116.4°, latitude 39.9°, and elevation 50m. The transmission rate parameters are obtained by the electronic device through real-time speed testing of the internet connection before the start of the current rendering cycle; for example, the current downlink transmission rate is 20Mbps.

[0035] The 3D city scene to be displayed is divided into a core focus area and a secondary buffer area based on spatial coordinates, distinguishing the spatial hierarchy of the scene. The maximum number of polygons allowed to be loaded in the current rendering cycle is calculated based on transmission rate parameters, quantifying network transmission capacity into a specific model face limit to avoid data requests exceeding network load and causing congestion. Based on the range of the core focus area and secondary buffer area, and the maximum number of polygons, the maximum number of polygons is asymmetrically allocated according to the preset business priorities of city models of different semantic types in the 3D city scene, and dynamic acquisition requests are generated to ensure that important areas and high-priority semantic types receive more polygon allocation quotas under limited network conditions. The dynamic acquisition requests are sent and received via the internet, reducing the network transmission of invalid data. The target model data stream is parsed, and differentiated rendering and display strategies are executed in the 3D city scene according to the semantic type of the target model data stream, allowing models of different semantic types to present different visual details, thereby improving the display efficiency of key city models.

[0036] Example 2

[0037] As a preferred embodiment of the present invention, based on Embodiment 1, the three-dimensional city scene to be displayed is divided into a core focus area and a secondary buffer area, using spatial location coordinates as reference points, including:

[0038] Extract the urban road network topology nodes that intersect with spatial location coordinates from the 3D urban scene to be displayed;

[0039] Calculate the topological connectivity cost extending from the spatial location coordinates to the topological nodes of the road network in the surrounding cities;

[0040] The continuous spatial range where the topological connectivity cost is less than the first cost threshold is defined as the core region of interest.

[0041] The continuous spatial range where the topological connectivity cost lies between the first cost threshold and the second cost threshold is defined as the secondary buffer region.

[0042] Specifically, such as Figure 2 As shown, the three-dimensional city scene pre-stores urban road network topology data. The urban road network topology data includes topology nodes composed of road intersections, road endpoints, etc., as well as topology edges connecting each topology node. First, the urban road network topology node that intersects with or is the nearest neighbor of the spatial location coordinates is extracted as the starting node. For example, if the spatial location coordinates fall near a certain intersection, the topology node corresponding to that intersection is extracted as the starting node.

[0043] Starting from the initial node, the system traverses and expands along the urban road network topology to the surrounding urban road network topology nodes, calculating the topological connectivity cost required to reach each surrounding urban road network topology node from the spatial location coordinates. The topological connectivity cost comprehensively considers factors such as road segment length, road grade, and traffic capacity. The specific calculation method is as follows: Topological connectivity cost = actual road segment length × road grade weight coefficient, where the road grade weight coefficient for main roads is 1.0, for secondary roads it is 1.5, and for branch roads it is 2.0. Taking the total length of the road segment from the initial node to an emergency rescue station as 800m and passing through a secondary road as an example, the corresponding topological connectivity cost is 800 × 1.5 = 1200.

[0044] After calculating the topological connectivity cost of each city's road network topological node, the continuous spatial range covered by each topological node with a topological connectivity cost less than the first cost threshold is defined as the core region of interest, and the continuous spatial range covered by each topological node with a topological connectivity cost between the first and second cost thresholds is defined as the secondary buffer region. For example, if the first cost threshold is set to 1500 and the second cost threshold is set to 4000, then the topological nodes with a topological connectivity cost less than 1500 and their associated spatial range constitute the core region of interest, the topological nodes with a topological connectivity cost between 1500 and 4000 and their associated spatial range constitute the secondary buffer region, and the region with a topological connectivity cost exceeding 4000 is not included in the model loading range of this rendering cycle.

[0045] This embodiment delineates regions along the urban road network topology, ensuring that the boundaries of the core focus area and secondary buffer areas align with the actual road routes. This avoids including inaccessible or high-cost detour areas within the core focus area, thereby making the asymmetric allocation of polygon counts more closely match the actual traffic structure around the target event and further improving the display efficiency of the key urban model.

[0046] Example 3

[0047] As a preferred embodiment of the present invention, based on Example 1, the upper limit of the number of polygons of the 3D model allowed to be loaded within the current rendering cycle is calculated according to the transmission rate parameter, including:

[0048] Get the real-time rendering frame rate parameters for the current rendering cycle;

[0049] Based on the transmission rate parameter, calculate the estimated number of the first polygons that satisfy the non-blocking transmission of the network.

[0050] Based on the real-time rendering frame rate parameters, calculate the estimated number of second polygons to satisfy the smoothness of the image.

[0051] By comparing the first estimated polygon count with the second estimated polygon count, the smaller of the two values ​​is determined as the upper limit of the polygon count.

[0052] Specifically, before the start of the current rendering cycle, the electronic device synchronously collects transmission rate parameters and real-time rendering frame rate parameters: the transmission rate parameters are obtained by real-time speed measurement of the current Internet connection, for example, the current downlink transmission rate is 100Mbps; the real-time rendering frame rate parameters are read in real time by the performance monitoring interface of the rendering engine, for example, the current rendering frame rate is 20fps, corresponding to the current rendering cycle duration of 1 / 20s=0.05s.

[0053] Based on the transmission rate parameters, the estimated number of the first polygons is calculated according to the preset network non-blocking transmission calculation model. The specific calculation formula is: estimated number of the first polygons = (transmission rate parameters × rendering cycle time × network utilization coefficient) / average data volume of a single polygon; where the network utilization coefficient is 0.8 to reserve bandwidth margin to avoid transmission congestion, and the average data volume of a single polygon is 40 bits; taking the above parameters as an example, the estimated number of the first polygons = (100 × 10^6 × 0.05 × 0.8) / 40 = 100,000.

[0054] Based on the real-time rendering frame rate parameters, the estimated number of second polygons is calculated according to the preset screen smoothness calculation model. The specific calculation formula is: estimated number of second polygons = maximum polygon rendering capacity of the device × frame rate compliance coefficient, frame rate compliance coefficient = real-time rendering frame rate parameter ÷ target frame rate; where the maximum polygon rendering capacity of the device is pre-calibrated by the graphics card hardware specifications, for example, the calibration value is 150,000, and the target frame rate is set to 60fps; taking a real-time rendering frame rate of 20fps as an example, the frame rate compliance coefficient = 20 ÷ 60 ≈ 0.33, and the estimated number of second polygons = 150,000 × 0.33 = 50,000.

[0055] Comparing the first estimated polygon count of 100,000 with the second estimated polygon count of 50,000, the smaller value of 50,000 is taken as the upper limit of the number of polygons of the 3D model that can be loaded in the current rendering cycle. That is, the current low rendering frame rate is the bottleneck constraint of this rendering cycle, and the total number of polygons loaded is controlled with the smoothness of the screen as the priority.

[0056] This embodiment also introduces a real-time rendering frame rate parameter, which independently estimates the number of polygons from two dimensions: network transmission capability and local rendering capability, and takes the smaller value of the two as the upper limit. This ensures that even when the network conditions are good but the local rendering performance is insufficient, the number of polygons loaded can still be controlled within the local rendering capability range, avoiding screen stuttering caused by the number of polygons exceeding the rendering capability. This further improves the display efficiency of key city models while ensuring screen smoothness.

[0057] Example 4

[0058] As a preferred embodiment of the present invention, based on Example 1, the upper limit of the number of polygons is asymmetrically allocated according to the preset business priorities of city models of different semantic types in the three-dimensional city scene to be displayed, including:

[0059] Identify the semantic types bound to the city model in the 3D city scene to be displayed. The semantic types are statically limited to key facility types, physical occlusion types, and visual decoration types.

[0060] Remove the polygonal assignments of city models with visual decorative types from all regions;

[0061] Prioritize allocating the maximum polygon count to the city model of key facility types within the core area of ​​concern, and calculate the first remaining polygon quota.

[0062] If the first remaining polygon quota is greater than zero, the first remaining polygon quota is allocated to the city model with physical occlusion type within the core area of ​​interest.

[0063] Specifically, each city model in the 3D city scene is pre-bound with a unique semantic type label during the modeling phase. The semantic type is statically limited to the following three categories: Key facility types, including city facility models with direct business significance in responding to target events, such as emergency rescue stations, hospitals, fire stations, and substations; Physical occlusion types, including city models that physically obstruct sightlines or paths, such as ordinary buildings, overpasses, and walls, but do not directly participate in business responses; and Visual decoration types, including city models that only provide visual background effects and do not substantially contribute to business judgment, such as green vegetation, landscape features, streetlights, and billboards. When performing asymmetric allocation, the semantic type labels of all city models in the core focus area and secondary buffer areas are first traversed. All city models of the visual decoration type are removed from the current polygon allocation plan, without being allocated any polygon quota or generating corresponding model data requests. This ensures that the maximum polygon count is entirely concentrated on city models with practical value for business display.

[0064] After removing city models of visual decoration type, starting from the maximum polygon count, the maximum polygon count is prioritized for allocation to all city models of key facility type within the core focus area. The number of polygons required for key facility type city models is calculated based on the high-precision level. For example, if there are 5 key facility type city models within the core focus area, and each model requires 8,000 polygons for high-precision rendering, then the key facility type city models will consume a total of 40,000 polygons. If the maximum polygon count is 100,000, then after the allocation of key facility types, the first remaining polygon quota = 100,000 - 40,000 = 60,000.

[0065] If the first remaining polygon quota is greater than zero, it will continue to be allocated to physically occluded city models within the core area of ​​interest. These physically occluded city models are arranged in ascending order of topological connectivity cost to their spatial coordinates, with priority given to allocating polygon quotas to those with lower cost. Calculations are performed using a medium precision level. For example, if the core area of ​​interest requires 50,000 polygons for all physically occluded city models, and the first remaining polygon quota of 60,000 can fully cover them, the second remaining polygon quota will be 10,000. If the first remaining polygon quota is insufficient to cover all physically occluded city models, allocations will continue in ascending order of topological connectivity cost until the quota is exhausted. Any remaining physically occluded city models without quotas will not be loaded in this rendering cycle. Critical facility city models within the secondary buffer area are only included in the allocation process if the second remaining polygon quota is greater than zero, and are calculated using a low precision level, with a lower priority than physically occluded city models within the core area of ​​interest.

[0066] This embodiment statically converges semantic types into three categories: key facility type, physical occlusion type, and visual decoration type. In terms of allocation logic, the polygon quota of the visual decoration type city model is completely eliminated. This avoids the consumption of rendering resources by models such as green vegetation and landscape features that do not contribute substantially to business judgment. This allows the limited upper limit of the number of polygons to be more focused on serving the display of city facilities with business value around the target event. In scenarios where transmission bandwidth or local rendering capabilities are limited, the display completeness of the key city model is further improved.

[0067] Example 5

[0068] As a preferred embodiment of the present invention, based on Example 4, the upper limit of the number of polygons is asymmetrically allocated according to the preset business priorities of city models of different semantic types in the three-dimensional city scene to be displayed, and further includes:

[0069] Calculate the second remaining polygon quota after the allocation of the core focus area;

[0070] Determine whether the second remaining polygon quota meets the minimum loading requirements for critical facility types within the secondary buffer zone;

[0071] If the minimum loading requirements are not met, the critical facility types in the secondary buffer area are downgraded and replaced with basic geometric bounding box models, and the corresponding preset number of basic polygons are allocated to the basic geometric bounding box models.

[0072] Specifically, after allocating polygon quotas for the key facility type city model and the physical occlusion type city model within the core focus area, the upper limit of the polygon quantity is reduced by the total polygon quotas already consumed by the two types of city models. The difference is the second remaining polygon quota. For example, if the upper limit of the polygon quantity is 100,000, and the key facility type city model within the core focus area consumes 40,000 polygons and the physical occlusion type city model consumes 50,000 polygons, then the second remaining polygon quota = 100,000 - 40,000 - 50,000 = 10,000 polygons.

[0073] After obtaining the second remaining polygon quota, the total number of polygons required to render all key facility type city models within the secondary buffer area at the minimum loading accuracy level is calculated. This total is taken as the minimum loading requirement for key facility types within the secondary buffer area. The minimum loading accuracy level is the minimum accuracy requirement for the semantic information that can be identified by the key facility type city model. For example, if there are 4 key facility type city models in the secondary buffer area, and each model requires 4000 polygons to render at the minimum loading accuracy level, then the minimum loading requirement = 4 × 4000 = 16000. The second remaining polygon quota of 10000 is compared with the minimum loading requirement of 16000. Since 10000 < 16000, it is determined that the second remaining polygon quota does not meet the minimum loading requirement for key facility types within the secondary buffer area.

[0074] If the minimum loading requirements are not met, the loading scheme for all key facility type city models in the secondary buffer area will be downgraded and replaced with the basic geometric bounding box model. The basic geometric bounding box model uses the spatial bounding box of the original key facility type city model as its geometric basis, and uses minimalist geometric forms such as cuboids or convex hulls to express the spatial occupancy information of city facilities. It retains the facility location, outline size, and semantic type labels, and does not load the fine geometric details of the original model. The preset number of basic polygons required for the basic geometric bounding box model is 12 polygons per model, that is, each of the six faces of the cuboid is composed of two triangular polygons. Taking the replacement of 4 key facility type city models in the secondary buffer area with the basic geometric bounding box model as an example, the total number of polygons consumed is 4 × 12 = 48, which is far less than the second remaining polygon quota of 10,000. After allocating 48 polygons to the basic geometric bounding box model, the remaining quota can continue to be allocated to the physical occlusion type city models in the secondary buffer area according to priority.

[0075] In this embodiment, when the second remaining polygon quota is insufficient to support the rendering of key facility types in the secondary buffer area at the lowest loading precision level, the basic geometric bounding box model is used to replace the original detailed model for loading. This allows the spatial location and outline information of key facilities in the secondary buffer area to still be presented in the 3D city scene with extremely low polygon consumption, avoiding the complete absence of key facilities in the secondary buffer area due to insufficient quota. This further improves the display completeness of key city models in scenarios where rendering resources are severely limited.

[0076] Example 6

[0077] As a preferred embodiment of the present invention, based on Example 1, a differentiated rendering and display strategy is executed according to the semantic type corresponding to the target model data stream, including:

[0078] Separate the first model data of key facility types and the second model data of physical obstruction types from the target model data stream;

[0079] The second model data is rendered using a semi-transparent wireframe material.

[0080] Turn off the depth test property of the first model data in the graphics rendering pipeline;

[0081] Apply a highlighted solid color material to the first model data after disabling the depth test attribute for overlay rendering.

[0082] Specifically, such as Figure 3 As shown, after the target model data stream is transmitted to the rendering module, the rendering module first reads the semantic type label carried by each city model data packet in the target model data stream, and splits the target model data stream into two independent data subsets according to the semantic type: city model data packets with semantic type label of key facility type are assigned to the first model data, and city model data packets with semantic type label of physical occlusion type are assigned to the second model data; city model data packets of visual decoration type have been removed in the asymmetric allocation stage of embodiment 4 and do not enter the target model data stream, so they do not participate in the rendering and display strategy of this embodiment.

[0083] The second model data is rendered using a semi-transparent wireframe material. The specific process is as follows: During the material binding stage of the graphics rendering pipeline, a preset semi-transparent wireframe material is uniformly bound to all physically occluded city models in the second model data. The parameter configuration of the semi-transparent wireframe material includes: wireframe color set to gray-white (RGB value 200, 200, 200), wireframe opacity set to 0.3, and face fill opacity set to 0.15. This allows the physically occluded city models such as buildings, overpasses, and walls to be presented in a semi-transparent outline form in the 3D city scene. Operators can directly observe the key facility city models within the occluded area through the semi-transparent wireframe of the physically occluded city models, eliminating the interference of physically occluded city models on the visual visibility of key facility city models.

[0084] The depth test attribute is turned off for the first model data. The specific process is as follows: During the rendering state configuration phase of the graphics rendering pipeline, the depth test switch of the graphics rendering pipeline is turned off for all key facility type city models in the first model data. After the depth test attribute is turned off, the pixel fragments of the key facility type city models will skip the depth buffer comparison stage during the rasterization stage. Regardless of whether the depth value of the key facility type city model in 3D space is covered by the depth value of the physically occluded type city model, the pixel fragments corresponding to the key facility type city model are forcibly written into the color buffer. From the rendering result, the key facility type city model is always displayed in front of the physically occluded type city model and is not occluded by any city model.

[0085] After disabling the depth test attribute, a highlighted solid color material is applied to the first model data for overlay rendering. The specific process is as follows: During the material binding stage of the graphics rendering pipeline, a preset highlighted solid color material is uniformly bound to all key facility type city models in the first model data. The parameter configuration of the highlighted solid color material includes: the fill color is set differently according to the specific business category of the key facility type city model; for example, emergency rescue stations are set to orange (RGB value 255,140,0), hospitals are set to red (RGB value 220,20,60), and fire stations are set to red (RGB value 255,69,0). The substation is set to yellow (RGB value 255,215,0), and the opacity is set to 1.0. Lighting calculations and shadow casting are not applied to ensure that the city model of the key facility type is presented in saturated solid color under any lighting environment. Overlay rendering is performed after the semi-transparent wireframe material rendering is completed. The rendering order is to first render the semi-transparent wireframe material of the second model data, and then render the bright solid color material of the first model data in overlay mode. This allows the city model of the key facility type to penetrate the semi-transparent wireframe of the physically occluded city model with a high-saturation solid color outline, forming a significant visual prominence effect in the rendered 3D city scene.

[0086] This embodiment uses a semi-transparent wireframe material for rendering city models with physical occlusion, and disables the depth test attribute and applies a high-brightness solid color material overlay for city models with critical facilities. This ensures that city models with critical facilities always maintain a transparent and bright display at the visual level, unaffected by the spatial occlusion of city models with physical occlusion. This significantly improves the visual recognition efficiency of critical city facilities in the complex spatial environment of 3D city scenes, assisting operators in quickly locating the spatial distribution of critical city facilities in target event response scenarios.

[0087] Example 7

[0088] As a preferred embodiment of the present invention, based on Example 1, the target model data stream is parsed, and in the 3D city scene to be displayed, a differentiated rendering and display strategy is executed according to the semantic type corresponding to the target model data stream, including:

[0089] The received target model data stream is parsed into basic topology data and additional detailed feature data;

[0090] In the 3D city scene to be displayed, the spatial outline of the corresponding city model is constructed first based on the basic topological structure data;

[0091] Based on the business priority order of semantic types, additional detailed feature data are asynchronously mapped to the corresponding spatial contours to complete the progressive rendering display.

[0092] Specifically, when the target model data stream enters the parsing phase of the rendering module, the data parser performs a structured split of the target model data stream according to a preset data frame structure. This splits the data package corresponding to each city model in the target model data stream into two independent data subsets: basic topology data and additional detail feature data. The basic topology data includes vertex coordinate arrays, edge connection lists, and face index tables that constitute the geometric shape of the city model, as well as the spatial transformation matrix of the city model (translation parameters, rotation parameters, scaling parameters). This is the minimum necessary dataset for the city model to perform spatial positioning and contour representation in a 3D city scene, and its data volume typically accounts for 15% to 30% of the complete model data package. The additional detail feature data includes the surface normal array, UV texture coordinate array, high-precision texture map file, normal map file, material parameter configuration (roughness parameters, metallicity parameters, self-illumination intensity parameters), and LOD level switching threshold of the city model. This is a supplementary dataset for achieving visual detail representation of the city model, and its data volume typically accounts for 70% to 85% of the complete model data package.

[0093] After data parsing is completed, the rendering module prioritizes reading the basic topology data. Based on the vertex coordinate array, edge connection list, and spatial transformation matrix in the basic topology data, it constructs the spatial outline of each city model in the target model data stream within the 3D city scene. The spatial outline construction stage only uses the geometric information in the basic topology data and does not wait for the transmission of additional detailed feature data to be completed. Therefore, the basic spatial form of the city model can be presented in the 3D city scene within a very short delay after the target model data stream begins to be received. Operators do not need to wait for the complete model data package to be loaded to obtain the spatial layout information of the city models around the target event. The spatial outline is filled with a default gray opaque planar material during the construction stage, and the spatial volume, position, and shape of the city model can be initially identified in the 3D city scene.

[0094] After the spatial outline is constructed, the rendering module asynchronously maps additional detail feature data onto the spatial outline according to the business priority order of semantic types: First, the additional detail feature data (including high-precision texture maps, normal maps, and high-precision material parameters) corresponding to the key facility type city model is asynchronously written into the spatial outline of the key facility type city model, completing the upgrade of the key facility type city model from spatial outline to complete high-precision rendering model; after the additional detail feature data of the key facility type city model is mapped, the additional detail feature data corresponding to the physical occlusion type city model is mapped to the spatial outline of the physical occlusion type city model in turn, completing the medium-precision rendering display of the physical occlusion type city model; the asynchronous mapping process of additional detail feature data is executed in an independent data loading thread, without blocking the main rendering thread. The spatial outline of each city model in the 3D city scene remains visible during the additional detail feature data mapping process, and gradually transitions from the basic outline appearance to the complete and detailed rendering appearance as the additional detail feature data is gradually written, forming a progressive rendering display effect.

[0095] This embodiment splits the target model data stream into two subsets: basic topology data and additional detailed feature data. It prioritizes using the smaller basic topology data to quickly construct the spatial outlines of each city model in a 3D city scene. Then, it asynchronously maps the additional detailed feature data to the spatial outlines according to the semantic type and business priority. This allows operators to obtain the full spatial layout of the city models surrounding the target event before the target model data stream transmission is complete. Key facility type city models are given priority for detailed rendering, which significantly shortens the waiting time for operators to obtain effective urban spatial information in the target event response scenario.

[0096] Example 8

[0097] Reference Figure 4This invention provides an internet-based digital city model display system, comprising:

[0098] The acquisition module is used to acquire the spatial coordinates of the target event and the transmission rate parameters of the current Internet connection;

[0099] The partitioning module is used to divide the 3D city scene to be displayed into a core focus area and a secondary buffer area, based on spatial location coordinates.

[0100] The calculation module is used to calculate the upper limit of the number of polygons of the 3D model that can be loaded within the current rendering cycle based on the transmission rate parameter.

[0101] The allocation module is used to asymmetrically allocate the maximum number of polygons based on the range of the core focus area and the secondary buffer area, as well as the upper limit of the number of polygons, according to the preset business priority of the city model of different semantic types in the 3D city scene to be displayed, and generate dynamic acquisition requests.

[0102] The transceiver module is used to send dynamic acquisition requests to the server via the Internet and to receive the target model data stream returned by the server based on the dynamic acquisition requests.

[0103] The rendering module is used to parse the target model data stream and execute differentiated rendering and display strategies based on the semantic type corresponding to the target model data stream in the 3D city scene to be displayed.

[0104] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for displaying digital city models based on the Internet, characterized in that, The method includes: Obtain the spatial coordinates of the target event and the current internet connection's transmission rate parameters; Using the aforementioned spatial coordinates as a reference point, the 3D city scene to be displayed is divided into a core focus area and a secondary buffer area. Based on the transmission rate parameter, calculate the upper limit of the number of polygons of the 3D model that can be loaded within the current rendering cycle; Based on the range of the core focus area and the secondary buffer area, and the upper limit of the number of polygons, the upper limit of the number of polygons is asymmetrically allocated according to the preset business priority of the city model of different semantic types in the 3D city scene to be displayed, and a dynamic acquisition request is generated. The dynamic acquisition request is sent to the server via the Internet, and the target model data stream returned by the server based on the dynamic acquisition request is received. The target model data stream is parsed, and a differentiated rendering and display strategy is executed in the 3D city scene to be displayed, based on the semantic type corresponding to the target model data stream.

2. The method for displaying a digital city model based on the Internet according to claim 1, characterized in that, The process of dividing the 3D city scene to be displayed into a core focus area and a secondary buffer area, using the spatial coordinates as a reference point, includes: Extract the urban road network topology nodes in the three-dimensional urban scene to be displayed that intersect with the spatial location coordinates; Calculate the topological connectivity cost extending from the spatial location coordinates to each of the surrounding urban road network topology nodes; The continuous spatial range where the topological connectivity cost is less than the first cost threshold is defined as the core region of interest. The continuous spatial range where the topological connectivity cost is between the first cost threshold and the second cost threshold is defined as the secondary buffer region.

3. The method for displaying a digital city model based on the Internet according to claim 1, characterized in that, The step of calculating the upper limit of the number of polygons of the 3D model allowed to be loaded in the current rendering cycle based on the transmission rate parameter includes: Obtain the real-time rendering frame rate parameters for the current rendering cycle; Based on the transmission rate parameters, calculate the estimated number of first polygons that satisfy non-blocking network transmission. Based on the real-time rendering frame rate parameters, calculate the estimated number of second polygons to satisfy the smoothness of the image. By comparing the first estimated polygon count with the second estimated polygon count, the smaller of the two values ​​is determined as the upper limit of the polygon count.

4. The method for displaying a digital city model based on the Internet according to claim 1, characterized in that, The step of asymmetrically allocating the upper limit of the number of polygons according to the preset business priorities of the city models of different semantic types in the 3D city scene to be displayed includes: Identify the semantic types bound to the city model in the 3D city scene to be displayed, wherein the semantic types are statically limited to key facility types, physical occlusion types, and visual decoration types; Remove polygon assignments from city models for all regions that describe the visual decoration type; The upper limit of the number of polygons is preferentially allocated to the city model of the key facility type within the core area of ​​concern, and the first remaining polygon quota is calculated. If the first remaining polygon quota is greater than zero, the first remaining polygon quota is allocated to the city model of the physical occlusion type within the core area of ​​interest.

5. The method for displaying a digital city model based on the Internet according to claim 4, characterized in that, The step of asymmetrically allocating the upper limit of the number of polygons according to the preset business priorities of city models of different semantic types in the 3D city scene to be displayed also includes: The second remaining polygon quota after the allocation of the core area of ​​interest is completed; Determine whether the second remaining polygon quota meets the minimum loading requirements of the critical facility type within the secondary buffer area; If the minimum loading requirements are not met, the critical facility type in the secondary buffer area is downgraded and replaced with a basic geometric bounding box model, and a corresponding preset number of basic polygons is assigned to the basic geometric bounding box model.

6. The method for displaying a digital city model based on the Internet according to claim 1, characterized in that, The step of executing a differentiated rendering and display strategy based on the semantic type corresponding to the target model data stream includes: Separate the first model data of the key facility type and the second model data of the physical obstruction type from the target model data stream; The second model data is rendered using a semi-transparent wireframe material; Turn off the depth test property of the first model data in the graphics rendering pipeline; Apply a highlight solid color material to the first model data after disabling the depth test attribute for overlay rendering.

7. The method for displaying a digital city model based on the Internet according to claim 1, characterized in that, The process of parsing the target model data stream and executing differentiated rendering and display strategies based on the semantic type corresponding to the target model data stream in the 3D city scene to be displayed includes: The received target model data stream is parsed into basic topology data and additional detailed feature data; In the three-dimensional city scene to be displayed, the spatial outline of the corresponding city model is constructed first based on the basic topological structure data; Based on the business priority order of semantic types, additional detailed feature data are asynchronously mapped to the corresponding spatial contours to complete the progressive rendering display.

8. A digital city model display system based on the Internet, characterized in that, The system includes: The acquisition module is used to acquire the spatial coordinates of the target event and the transmission rate parameters of the current Internet connection; The partitioning module is used to divide the 3D city scene to be displayed into a core focus area and a secondary buffer area, based on the spatial location coordinates. The calculation module is used to calculate the upper limit of the number of polygons of the 3D model that can be loaded within the current rendering cycle based on the transmission rate parameter. The allocation module is used to asymmetrically allocate the upper limit of the number of polygons based on the range of the core focus area and the secondary buffer area, as well as the upper limit of the number of polygons, according to the preset business priority of the city model of different semantic types in the 3D city scene to be displayed, and generate dynamic acquisition requests. The transceiver module is used to send the dynamic acquisition request to the server via the Internet and to receive the target model data stream returned by the server according to the dynamic acquisition request. The rendering module is used to parse the target model data stream and execute differentiated rendering and display strategies in the 3D city scene to be displayed, based on the semantic type corresponding to the target model data stream.

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