CN101119485A - Characteristic reservation based three-dimensional model progressive transmission method - Google Patents
Characteristic reservation based three-dimensional model progressive transmission method Download PDFInfo
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Abstract
The present invention relates to a three-dimensional model progression transmission method on basis of keeping character, the present invention holds the improvement for character keeping on the basis of the simplified arithmetic of the original three-dimensional model, and at the same time of simplifying the geometrical model, the present invention keeps the topological property and attribute character of the model, and gets the underlying net with smaller data amount, and on the basis of above, the processing coding is held distributed on basis of octree to construct the procession net document. When in transmission, the octree broadness prior coding underlying net is firstly used, and then adopting the procession net transmission method to transport a serial detail recovering information, and continuousely improving model presicion and recovering the original document, thereby solving the problem that: the responding time for the traditional transmission method is long. In adition, the viewpoint related transmission strategy facing the object is designed for the three-dimensional scene, increasing the actural drawing, and making the visibility judging of the object is carried out by putting on the clinet end, and reducing the loading of the server.
Description
Technical Field
The invention relates to the technical field of three-dimensional model simplification, geometric compression coding, progressive transmission and the like, in particular to a characteristic-retaining three-dimensional model progressive transmission method which can be applied to processing and network release of various three-dimensional models with complex textures and structural characteristics. In addition, the method is also applied to the network publishing of precious cultural relics in a digital museum.
Background
In computer graphics, complex three-dimensional shapes are typically described using triangular meshes. With the continuous progress of three-dimensional data capture technology, the data volume of the grid can be huge, which brings many difficulties to the storage, transmission and drawing of the three-dimensional model. The digital museum comprises a large number of three-dimensional models which need to be displayed on the internet, and the bottleneck limit of network transmission needs to be solved for the most basic transmission of single-model exhibits and complex real-time free-play of large-scale scenes.
The network transmission of the traditional single-resolution model adopts a Download-and-Display (Download-and-Display) mode, that is, all the related data of the three-dimensional model is downloaded to the client and then displayed. The disadvantage of this approach is that the user wait time is too long. The improvement is a progressive grid method proposed by Hoppe (see Hoppe H. Progressive nets. ACM Computer Graphics,1996, 30 (1): 99-108), that is, vertex deletion (see Schroeder W. Definitions of Triangle nets. Computer Graphics,1992, 26 (2): 65-70), quadratic Error (see Garland M. Surface simulation using quadratic Error metrics. Computer Graphics,1997, 31 (3): 209-216) and other model Simplification algorithms are firstly adopted to obtain a multi-resolution model, and each step is recorded in the Simplification process, so that the original grid model is decomposed into a rough base grid and a series of detail optimization information which can be reversely restored to the base grid; in the transmission process, firstly transmitting the base grid to a client and displaying, then gradually transmitting detail optimization information, and refining the initial rough model; such a lossless model reconstruction and encoding method can give a user a response in a short time and can stop transmission at any time, which is a progressive transmission method in a Download-while-Display (Download-while-Display) mode.
For the progressive mesh method, many methods are improved later, however, most of the methods are processed aiming at a relatively regular geometric model without attributes, do not relate to attribute information such as textures and the like, and do not support a three-dimensional scene. In the practical application field, no matter a single model or a three-dimensional scene, not only contains geometric and topological information, but also often contains attributes such as color and texture, and boundaries and holes inevitably exist, so that a proper method needs to be adopted, and the characteristic information is kept while simplification is realized. In addition, many methods only use model simplification to obtain progressive grid files, and do not further compress model data, if progressive grids and compression coding can be combined to reconstruct model files, the method is more beneficial to reducing model data quantity and improving real-time response of model transmission browsing.
Disclosure of Invention
The technical solution of the present invention is: the method is based on the characteristic retention, namely the topological property and texture or color attribute characteristics of the original model are retained in the processing process, the model has high reality retaining performance, the requirements on network bandwidth and client machine performance are low, and the progressive transmission of the three-dimensional scene is supported.
The technical solution of the invention is as follows: a three-dimensional model progressive transmission method based on feature preservation is characterized by comprising the following steps:
(1) Simplifying the retained features of the original grid model to form a rough base grid;
(2) Implementing octree compression coding on the base grid to form a progressive grid file;
(3) Adopting a progressive transmission mode of octree decoding-progressive grid transmission under a Browser/Server structure;
(4) And transmitting the three-dimensional scene by adopting an object-oriented viewpoint related transmission strategy on the basis of the steps.
In the simplification, a triangle folding method for reserving topological boundary and texture or color attribute is adopted, and the main operation steps are as follows:
(1) Classifying the original triangular mesh: boundary triangles, corner triangles, internal triangles and characteristic triangles;
(2) According to the classification of the triangle, different error measurement methods are adopted:
a. for internal triangles, T is for each triangle i Provided with a 4 x 4 error matrix Q i And assume that the new point after folding is v i Defining the folding error of the triangle as
By minimizing the error to obtain v i A location;
b. for the corner point triangle, defining new point v after folding i Calculating a folding error for a vertex on the primary boundary by adopting the same method as the step a;
c. the folding error is set to a maximum value for the boundary triangle and the feature triangle.
(3) And after the folding errors of all the triangles are obtained, selecting the triangle with the smallest error to perform the folding operation.
In the step (3), a method of combining geometric compression decoding and progressive mesh is adopted in the transmission process, and the steps are as follows:
(1) In the initial transmission stage, an octree breadth-first traversal decoding mode is adopted until the transmission of the base grid data is finished;
(2) And a progressive grid transmission mode is adopted to keep the continuous improvement of the model precision under higher similarity.
The step (4) of adopting an object-oriented viewpoint-related transmission strategy for the three-dimensional scene comprises the following steps:
(1) Constructing a single data stream for each object in the scene, and adopting the progressive transmission mode of the octree decoding-progressive grid transmission for each data stream;
(2) The method comprises the steps that downloading, analyzing and drawing threads are arranged on a client side, synchronous control is conducted, and parallel transmission of objects is guaranteed;
(3) Calculating viewpoint information at a client, and judging the current object to be transmitted according to the visibility of the view cone;
(4) The server receives the needed object mark transmitted by the client and sends corresponding optimization information.
Compared with the existing release method, the invention has the following advantages:
(1) Original model topological property and texture/color attribute are reserved
Most of the traditional methods are processed aiming at a more regular geometric model without attributes; in the field of practical application, three-dimensional data not only contains geometric and topological information, but also often contains attributes such as color and texture, and boundaries and holes inevitably exist, and the information plays an important role in maintaining the appearance and the sense of reality of the model and must be preserved in a simplified process.
The invention provides a simplifying method of a non-closed grid model combined with attributes based on a triangular folding method, which not only effectively controls the geometric error between a simplified grid and an original grid, but also better keeps the topological boundary, color, texture, normal vector and other attributes of a three-dimensional model, and has wider application range and higher practicability compared with the traditional method.
In addition, the model simplification algorithm of the invention can specify the accuracy degree of model simplification according to the retention requirements of users on different proportions of geometry/attributes, and for an initial model of hundreds of thousands or even millions of polygons, after the initial model is simplified by 99%, the high geometric similarity and boundary topology structure and attribute characteristics can be still maintained.
(2) Flexibility in network bandwidth and client machine performance requirements
In the traditional three-dimensional transmission mode of 'downloading and displaying firstly', all relevant data of the three-dimensional model need to be downloaded to a client and then displayed. Therefore, the requirement on network bandwidth is high, and the mode cannot be applied to three-dimensional models with scales exceeding million polygons; in addition, the graphics processing capabilities of different client machines are different, and the same model may already be difficult for some users to process, but other users may also need higher precision effects.
The remote rendering system proposed in recent years is a Client/Server structure, a Client is responsible for receiving input of a user and sending a corresponding rendering request to a Server, and a Server with high graphics performance is responsible for rendering and transmitting an obtained image back to the Client sending the request for display.
The progressive transmission mode based on the Browser/Server structure is adopted, only one rough base grid with small data volume needs to be transmitted to the client, the client can display the data immediately after receiving the base grid data, then the Server continuously transmits the optimization information of the base grid, and the display effect of the client is gradually refined until the transmission is finished or the requirement of a user on the model fineness is met. Therefore, a user can select a model with corresponding precision to check according to the requirement of the user and the performance of the machine, and can suspend or continue transmission at any time; since the rendering task is shared to each client, more users can be supported to the maximum extent.
(3) Short response time and high fineness degree
The biggest problem of the method of 'downloading before displaying' is that the response time is too long, and the display can be started after the whole model is downloaded.
Progressive grid transmission is used as a fine-grained model multi-resolution division scheme, after base grid data are obtained, the coarse model rendering and refining process can be started immediately, and a model with higher accuracy than other methods can be provided; but the disadvantage is that it takes a long time to recover the complete highest resolution model compared to the non-progressive method; in addition, although the conventional progressive transmission method is "display while downloading" in the whole process, it still needs to wait for the base mesh data to be completely downloaded in the beginning stage before displaying and progressively updating, and for the three-dimensional model with higher precision and containing attributes such as texture/color, etc., the base mesh data amount is still larger after being processed by a simplified method, for example, the size of the base mesh file after the three-dimensional model with the number of polygonal planes of 1000000 is simplified by 99% is still as large as 3MB, and the required download time is also intolerable in the case of low bandwidth.
The geometric progressive compression based on the tree structure is a coarse-grained model multi-resolution partitioning scheme, the model can be displayed from zero, and the geometric data of the model is updated in batches along with the transmission and decoding of recovery information, so that the response time is reduced to the maximum extent; due to effective compression in batches, the generated model file data volume is smaller and the total transmission time is much shorter than that of a progressive grid method; however, the method has the disadvantages that the improvement of the resolution of the model is discontinuous, jump exists, and the accuracy of the model in the recovery process is lower than that of a progressive grid method.
The invention combines the advantages of progressive grid and geometric compression, further compression coding is carried out on the base grid on the basis of grid simplification, and an octree breadth-first traversal decoding and progressive grid transmission combined recovery scheme is adopted, and a compression decoding transmission mode is adopted at the transmission initial stage with high requirement on response time and low requirement on model accuracy until the base grid data transmission is finished; and then, a progressive grid transmission mode is adopted, so that higher and continuous model resolution improvement is kept, and a user can stop at any time, so that the response time is further shortened.
(4) Supporting three-dimensional scenes
The three-dimensional model includes an object model and a three-dimensional scene, and the three-dimensional scene is composed of different objects, wherein each object is an independent body or structure. Most of the traditional methods only process the object model and do not consider the three-dimensional scene.
The invention regards the scene model as a combination of a plurality of object models, and simplifies each object in the combination by a mesh with completely reserved topological boundary, thereby achieving the purpose of simplifying the whole model. In the transmission recovery stage, multiple data streams are used, each object forms an independent data stream, a transmission strategy related to a view point is adopted, and the transmission of the current visible object is controlled, and all objects are ensured to be in a uniform world coordinate system, so that a complete original model can be recovered.
Drawings
FIG. 1 is a system implementation flow of the present invention;
FIG. 2 is a simplified feature-preserving experimental result of a three-dimensional model according to the present invention;
FIG. 3 is a perspective-dependent transport framework for a three-dimensional scene according to the present invention;
FIG. 4 is a process of the present invention for incrementally transmitting a luni-solar model;
fig. 5 is a process of performing viewpoint-dependent decoding transmission on a three-dimensional scene containing 25 terracotta soldiers and horses according to the invention.
Detailed Description
The invention comprises three aspects of model simplification, compression coding and progressive transmission, and the implementation flow is shown in figure 1.
1. Three-dimensional model simplification
The method adopts a triangle folding algorithm based on quadratic errors to simplify the three-dimensional model, and retains the topological boundary and attribute characteristics of the model while simplifying. The basic operation of the algorithm is triangle collapsing contraction, i.e. by folding the triangle T i Performing a folding operation to merge its three vertices into a vertex v i Thereby simplifying the original mesh.
The algorithm firstly classifies all triangles in the original mesh according to the following division principle:
for each triangle in the mesh model, if a certain edge thereof is owned by only one triangle (i.e., the triangle), the edge is a boundary edge, and the triangle is a boundary triangle; for non-boundary triangles, if at least one vertex is on a boundary edge, the vertex is a boundary point, and the triangle is an angular point triangle; if none of the three vertices are on a boundary edge, the triangle is an interior triangle.
For models containing color attributes, the average of the color values of the three vertices of each triangle is used as the equivalent color value for that triangle if the difference between the color value of the current triangle and the color value of its surrounding neighbors exceeds a pre-specified threshold τ, i.e.
Then mark the triangle as a feature triangle, where [ r i g i b i ] T 、[r p g p b p ] T Are respectively triangular T i 、 T p The threshold τ may be selected according to different requirements of the user on the retention degree of the geometric and attribute features, and the higher the requirement on the attribute details is, the smaller the τ value is, and otherwise, the larger the τ value is.
In addition, for the texture, a similar method is adopted for processing; the difference is that the color information of the corresponding vertex is obtained from the texture image through the texture coordinate, and then the texture equivalent color value of the triangle is calculated.
Then, the geometric folding error of each triangle is calculated:
(1) For each internal triangle T in the original mesh i Provided with an error matrix Q i If, ifTriangle T i Folding to a point v i ＝[x i y i z i 1] T Then define the folding error of the triangle as the sum of the squares of the distances from the new point to all the adjoining triangle planes of the original triangle:
where p = [ abcd ]] T Representation and triangle T i The plane equation ax + by + cz + d =0 for the plane of each triangle in the adjoining triangle set (where a is 2 +b 2 +c 2 = 1). The error criteria given by the above equation can then be converted to the following quadratic form:
wherein M is p Is a symmetric 4 × 4 matrix, which can represent the secondary distance from any point in the triangular mesh to the plane:
and the error matrix Q i Planar quadratic matrix addition for all adjoining triangles
For v i The position is selected by calculating to make epsilon (T) i ) Is obtained with the smallest value.
(2) For each corner triangle, defining a new point v after it is folded i Is a vertex on the primary boundary and passes through
Calculating a folding error;
(3) The folding error is set to the maximum for the boundary triangle and the feature triangle.
After the folding error of each triangle is obtained, the triangles are arranged according to the final error from small to large, and the triangle with the minimum folding error is selected from the triangle sequence to execute the folding operation, so that the boundary triangle and the characteristic triangle are ensured not to participate in folding on the premise of keeping the geometric similarity, and the boundary and attribute details of the model are reserved.
By using the above simplification method, the model is still very close to the original model after being simplified by 70%, and when the model is simplified by more than 90%, the obtained result can still better retain the boundary, contour and attribute characteristics of the original model, besides being acceptable in geometric similarity, as shown in fig. 2.
And recording the vertex coordinates of the triangles participating in the collapsing disappearance and the information of the related triangles to construct a progressive mesh file while simplifying the model, thereby supporting effective incremental transmission. For models containing attributes, the vertex coordinate expression can be extended, and the vertex information is expressed as v i (x i ，y i ，z i ，) Wherein x is i ，y i ，z i Is the coordinate of the vertex, and the coordinate of the vertex,
scalar attributes corresponding to the vertices (e.g. for color attributes,
representing RGB color values; with respect to the attribute of the texture,
surface texture coordinates), through the above processing, can be obtainedThe attribute information is recorded in a progressive mesh file to provide recovery of the attributes while reconstructing the original geometric model.
2. Base mesh compression encoding
The invention carries out compressed coding based on octree division on the simplified base grid, quantizes the geometric coordinates of the vertexes by 12 bits, and mainly comprises three steps:
(1) The multi-resolution hierarchical organization of the octree is carried out on the vertexes of the geometric model until the most refined tree nodes can express the quantized precision: firstly, setting a minimum bounding box for a model, and carrying out recursive subdivision according to an octree partitioning method, wherein each tree node records the number of top points contained in a subtree, tree nodes without top points are not sub-divided continuously, and tree nodes containing top points are sub-divided iteratively until the nodes are empty or only contain one top point and reach a maximum precision layer; the leaf node centers in the generated octree implicitly represent the spatial locations of the vertices they contain.
(2) Traversing each node of the octree in a breadth-first mode from coarse to fine, and outputting a data stream describing the position condition of the vertex: according to the number of vertexes contained in the node, for each non-empty node, identifying whether the node is a single node by using 1 bit; for a single node, identifying which child node in the single node contains a unique vertex by using 3 bits; for a non-empty non-single node, an 8bits mark is generated to indicate whether a child node of the node is non-empty; and circulating the steps until the nodes accessing the finest layer stop.
(3) And (3) carrying out rearrangement and compression of vertex indexes on the topology data: and rearranging vertex indexes in the order of left to right of the vertexes contained in the leaf nodes, updating corresponding index values in the original topology data, and compressing the topology data.
(4) Arranging and compressing the attribute information in advance according to the sequence of leaf vertexes of the geometric node flow: and arranging the attribute information in advance according to the sequence of the leaf top points of the geometric node flow, and synchronizing the attribute information with the geometric information in the encoding process.
(5) All data streams are arithmetically encoded.
After compression coding is adopted, the file amount of the base grid is further reduced.
1. Progressive transmission
The invention adopts a progressive transmission mode of octree decoding-progressive grid transmission under a Browser/Server structure. In the transmission decoding stage, firstly, a layer-by-layer refinement mode based on octree breadth-first traversal is adopted to recover a base grid; after the transmission of the basic grid information is finished, a progressive grid transmission mode is continuously adopted to transmit a series of detail recovery information, and the model is optimized and recovered.
(1) Browser-server
According to the method, the Java Applet embedded in the Web browser is used at the browser end, so that the three-dimensional model can be rendered without installing an independent application program by a user; the user can perform interactive operations such as rotation, translation, zooming and the like on the model, and can also roam and walk in a scene to check an interested region and the like; in addition, because of adopting the progressive compression and transmission strategy, the response time is greatly shortened, and the method is more suitable for the online browsing of common users.
In the process of three-dimensional data transmission, a user can control transmission suspension at any time when needing to check and operate a model, at the moment, a browser end sends a waiting request to a server, the request comprises the current data stream position and state, and the server suspends data transmission; and when the user stops operating, the browser sends a downloading request to the server, and the server continues to send data to the browser according to the stored state information, so that the thinning process of the three-dimensional model is continued.
(2) Communication thread and management thereof
In order to achieve the purpose of progressive transmission, model rendering needs to be performed while file data is downloaded, so that a multi-thread implementation mode is adopted.
The server sequentially transmits the model files to the client, the client analyzes data content while receiving the data, and different internal model data representations are constructed according to different contents so as to start drawing; at the same time, when every new message arrives, the internal data content needs to be updated, and the image in the screen needs to be updated again. Here, three threads are needed, respectively: a data download thread, a data analysis thread, and a graphics rendering thread (main thread).
The downloading thread is responsible for downloading file data from the server side, and when the client side has data, the client side is handed to the analysis thread to carry out semantic analysis on the data to form an internal data description format. The drawing thread is responsible for displaying these internal data on the screen. In the subsequent process, every time a new message is received, the new message is converted into an internal data description and then displayed; this is repeated.
In this process, the problem of synchronization between threads needs to be solved: first, it makes no sense for the download thread and the analysis thread to analyze before the data is downloaded, which requires synchronization between the two threads; secondly, when the analysis thread analyzes the downloaded file data, the download thread may download new data and request to update the file data, which requires mutually exclusive access of data between the two threads; similarly, there is a problem between the analysis thread and the drawing thread, and the drawing thread can only display after the analysis thread is partially completed (the analysis of several pieces of optimization information is completed), and there is a mutual exclusion between them.
The three threads are used for realizing the exclusive access to the resources by the critical section, and when the downloading thread does not download the data to the local part of the client, the analysis thread can only wait and can only work after the data is obtained. According to the difference of the speeds, the method can be divided into two cases:
(1) The download speed is slower than the analysis speed: after the current data segment is analyzed, the analysis thread needs to determine its own running state according to the current downloaded state. If the current file is not downloaded completely, continuing waiting for the next section of data to arrive; and if the current file is downloaded, the analysis is finished.
(2) The downloading speed is faster than the analysis speed: at this time, the data to be analyzed is always present for the analysis thread, and only the arrival of the first data needs to be waited for at the beginning.
The synchronization between the analysis thread and the drawing thread is simple, so long as the drawing thread can draw after the new data analysis is finished.
1. Three-dimensional scene transmission
A three-dimensional scene is composed of different objects, where each object is an independent form or structure. For this purpose, in the simplification and coding phase, the three-dimensional scene is regarded as an assembly of several object models, and each object in the three-dimensional scene is subjected to mesh simplification with completely reserved topological boundaries, and in the transmission recovery phase, a multi-data-stream method is used, and an object-oriented viewpoint-dependent transmission strategy is adopted, so that different model objects are selected for optimization according to different viewpoints of users.
A separate data stream is first established for each object of the scene, so that for each data stream, the aforementioned progressive transmission mode of octree decoding-progressive mesh transmission can be employed. Unlike simple object model transmission, the invention designs an object-oriented viewpoint-related transmission framework, as shown in fig. 3, a server side provides model data and stores the transmission state of the current model object, and a client side downloads the data and reconstructs and renders the model. Besides downloading, analyzing and drawing threads, a visibility judgment thread is added for the client side to calculate viewpoint information and judge an object to be transmitted according to the visibility of a viewing cone; the server only needs to receive the required object mark transmitted by each client, and then the corresponding optimization information can be transmitted. In this way, the calculation load is distributed to each client, so that the efficiency of the server is improved; for the client, because the visibility judgment is coarse-grained object-oriented, a large amount of calculation cannot be caused, and the visual effect is not influenced.
The whole execution process of the framework is as follows:
(1) A client sends a scene transmission request to a server;
(2) The server receives a client request, establishes a connection with the client, checks whether the model data requested by the user is called into the memory or not, calls the model data into the memory if the model data requested by the user is not called into the memory, and then establishes an octree for each object of the scene;
(3) The server transmits to the client the base mesh data (coordinates of vertices, indices of faces, and other relevant information) for each object;
(4) After receiving the basic grid information, the client displays the basic grid information;
(5) The client calculates the current visible object according to the own viewpoint and transmits the visibility state to the server;
(6) The server transmits the optimization information of the current visible object according to the current client state, suspends the transmission of the optimization information data streams of other objects, and saves the current state;
(7) The client refines the model and redraws the model every time the client receives one piece of optimization information;
(8) Repeating the above (5) if the viewpoint is changed;
(9) The client quits, and the server clears useless state information.
The model is progressively transmitted by using the transmission method, and fig. 4 shows the transmission of a kwan-yin model, in which octree decoding is firstly performed, and progressive grid transmission recovery is further performed after a base grid is obtained. As can be seen from the transmission process of fig. 4, the base mesh obtained after the octree is started and decoded for 20% transmission is close to the original model in geometric similarity, and the boundary, contour and texture features of the original model are well preserved.
Fig. 5 is a process of progressively transmitting a group of terracotta warriors models in a scene, the initial process is still similar, and at first, octree decoding transmission is performed on the currently visible terracotta warriors models; then, the viewpoint is drawn closer, and part of objects enter the visual field and participate in thinning; when the viewpoint continues to rotate, the terracotta warriors model originally outside the window still appears to be rough because the terracotta warriors model just starts to be transmitted.
Claims (4)
1. A three-dimensional model progressive transmission method based on feature retention is characterized by comprising the following steps:
(1) Simplifying the retained features of the original grid model to form a rough base grid;
(2) Carrying out octree compression coding on the formed rough base grid to form a progressive grid file;
(3) Adopting a progressive transmission mode of octree decoding-progressive grid transmission under a Browser/Server structure;
(4) And transmitting the three-dimensional scene by adopting an object-oriented viewpoint related transmission strategy on the basis of the steps.
2. The feature preservation-based three-dimensional model progressive transmission method according to claim 1, characterized in that: in the step (1), the original mesh model is simplified by adopting a method for retaining topological boundary and texture or color attribute based on triangle folding, and the steps are as follows:
(1) Classifying the original triangular mesh: boundary triangles, corner triangles, internal triangles and characteristic triangles;
(2) According to the classification of the triangle, different error measurement methods are adopted:
a. for internal triangles, T is assigned to each triangle i Provided with a 4 x 4 error matrix Q i And assume that the new point after it is folded is v i Defining the folding error of the triangle as
By minimizing the error to obtain v i Position;
b. for the corner point triangle, defining a new folded point vi as a vertex on the primary boundary, and calculating a folding error by adopting the same method as the step a;
c. the folding error is set to the maximum for the boundary triangle and the feature triangle.
(3) And after the folding errors of all the triangles are obtained, selecting the triangle with the smallest error to perform the folding operation.
3. The feature preservation-based three-dimensional model progressive transmission method according to claim 1, characterized in that: and (4) in the initial transmission stage in the step (3), an octree breadth traversal decoding mode is adopted until the transmission of the base grid data is finished, and then a progressive grid transmission mode is adopted to keep the continuous improvement of the model precision.
4. The progressive transmission method of the three-dimensional model according to claim 1, wherein: the step (4) of adopting an object-oriented viewpoint-related transmission strategy for the three-dimensional scene model comprises the following steps:
(1) Constructing a single data stream for each object in the scene, and adopting the progressive transmission mode of the octree decoding-progressive grid transmission for each data stream;
(2) The method comprises the steps that downloading, analyzing and drawing threads are arranged on a client side, synchronous control is conducted, and parallel transmission of objects is guaranteed;
(3) Calculating viewpoint information at a client, and judging the current object to be transmitted according to the visibility of the view cone;
(4) The server receives the needed object mark transmitted by the client and sends corresponding optimization information.
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