CN101408990B - Progressive compression and transmission method for urban architecture model - Google Patents

Abstract

The invention discloses a processing method of building models by a computer, in particular to a progressive compression and transmission method of three dimensional city models. The method includes the following steps: classification is carried out on city roads, boundaries, subdistricts, building notes, landmarks and the like, and then numerical calculation is carried out by certain calculation methods; numerical value combination is carried out according to specific combination orders; certain tree models are adopted in the process of combination, then technological means such as coding and compression and the like are carried out, thus obtaining code streams from a sever continuously and displaying the three dimensional city models on a computer screen from vague to clear by utilizing computer drawing methods. The method has the advantages that a series of layered compressed code streams are used for expressing a complex city building model scene; besides, the data stream on each layer is less than the amount of original model data, thus reducing data memory space of the scene. The invention can be applied to a large-scale city roaming system.

Description

A kind of progressive compression and transmission method of urban architecture model

Technical field

The present invention relates to a kind of computing machine to the BUILDINGS MODELS disposal route, refer in particular to a kind of progressive compression and transmission method of three-dimensional city model.

Technical background

Three-dimensional city model (3DCM) is described as the three dimensional lifelike in city, and the application model with true expressive force is provided for association areas such as urban construction and planning.The three-dimensional city model is set up from the three dimensional computer modeling in Britain Bath city, from the nineties in 20th century bigger development has been arranged, and has received concern more and more widely, and has obtained large-scale application.

In the three-dimensional sight of city, buildings and landform are the types of ground objects that needs most concern in the city.Yet, moulding is abundant, quantity mega structure object model is one of important symbol of urbanization construction, building model occupies quite great proportion in the three-dimensional city model, the effect of visualization of building model has the irreplaceable effect of other types of ground objects for the expression true to nature of whole three-dimensional city model.

Yet, the contradiction the when textural characteristics true to nature of the photograph texture that building model had and complicated three-dimensional geometrical structure have caused the three-dimensional city model to use between high fidelity performance and the system performance.Consider that different professional domains show the demand that has in various degree to the sense of reality of building model, (Level ofdetail, LOD) technology becomes one of effective ways in the three-dimensional city model investigation to detail.

The LOD theory is widely used in flight simulation, fields such as quick drafting, interactive visual and the virtual reality of complex three-dimensional scene.To the object in Same Scene or the scene, use the describing method of different details to obtain a group model during its basic thought, in graphic plotting, select suitable level of detail model to draw according to viewpoint.The LOD descriptive model more meets people's cognitive characteristics, be to improve Real-Time Scheduling to play up the important channel that the speed reconciliation is never analyzed with 3D under the yardstick on the one hand, be in data on the other hand and obtain diversity with application demand, different application often will be produced the model data of different level of detail.

The LOD technology can be divided into static LOD technology and dynamic LOD technology two classes.Static LOD technology generates and stores a plurality of simplified models in advance, and its advantage has been to omit the processing time of real-time simplified model, has taken more storage space on the other hand, and switches the sudden change that can produce visual effect between the model of different fine degree.Dynamically the LOD technology dynamically generates simplified model according to viewpoint, and purpose is to guarantee the ground transition of model continuously smooth, the sudden change that does not produce visual effect.

At present, the most models shortcut calculation mainly is the simplification at general geometric model, particularly to continuous free grid surface, in three-dimensional city model investigation and technology, the technology of Terrain LOD on a large scale based on True Data has obtained suitable progress, the continuous LOD algorithm of many rule-based grids has been realized the real-time reality of large-scale terrain, wherein representational real-time continuous LOD algorithm (the Continuous Level ofDetail that has based on quaternary tree, CLOD), the adaptive grid algorithm of real-time optimization (Real Time Optimally Adapting Meshes, ROAM) and the relevant progressive trellis algorithm of viewpoint (ViewDependent Progressive Meshes, VDPM) etc.

Yet, compare with the progress that large-scale terrain LOD landform is obtained, the research of the detail of the such irregular geometry of buildings still is in the junior stage.Because a large amount of cultures' geometric shape presentation is widely different, be difficult to its level of detail is carried out unified quantification regulation, need consider respectively according to factors such as the serviceability of three-dimensional city model data and the property obtained.So far, how to plan and to express detail, compression and the transmission of the building model in the three-dimensional sight of city effectively, the characteristics of obtaining each level of detail model of conditional plan according to different application scope and data become that the three-dimensional city model is used and one of digital urban construction urgent problem.In addition, the LOD method of most existing urban architecture model all is a static type, does not support the requirement of progressive transmission, and the expression data volume of scene increases the feasible data transmission burden that increases scene.

Summary of the invention

The present invention is directed to the disadvantages of background technology part, purpose provides a kind of progressive compression and transmission method of urban architecture model, according to this method, the urban architecture model scene of a complexity can be expressed as the code stream form of the compression of a series of layerings, and every layer data stream helps Network Transmission much smaller than original model data amount.

The present invention realizes that geometrical property that the method for purpose is based on BUILDINGS MODELS in the scene carries out with similar building geometric model that iteration is closed and carry out effective shape and approach, and it comprises the steps:

Step 1: the three-dimensional city model is classified, be divided into road, border, sub-district, building node and terrestrial reference;

Step 2:, obtain its minimum direction and surround the polygon box to each BUILDINGS MODELS; The distance metric of two buildingss is the distance of its minimum polygon bounding box, is defined as follows:

$d(P,Q)=\frac{\mathrm{Area}\left(P\right)\·\mathrm{Area}\left(Q\right)}{{\left(\mathrm{Area}(P\∪Q)\right)}^{\mathrm{\α}}}{d}_H(P,Q)$

P in the formula, Q are the minimum polygon bounding box of 2 buildings, and Area (P) is the area of P in the projection on ground, and Area (Q) is the area of Q in the projection on ground, Area (P _UQ) be P and the Q area in the projection of ground surface union part, α is the distance calculation parameter greater than 0, d _H(P, Q) be P and Q in the subregional Hausdorff distance of floor portion, the unit of each numerical value is identical measurement unit, as all being meter, centimetre, square metre or square centimeter etc.

As preferably, the progressive compression and the transmission method of above-mentioned a kind of urban architecture model, the parameter alpha of described distance calculation is between the 1-3.As better selection, the parameter alpha of described distance calculation is 2.

Step 3: BUILDINGS MODELS is carried out the union operation of level, specifically comprise

(1) to the BUILDINGS MODELS that belongs to same sub-district according to building orientation, distance, information such as orientation merge;

(2),, also merge according to information such as the distance of sub-district, orientation if they are not in the both sides of road to different districts;

(3) in each merging process, keep boundary information;

(4) in each merging process, some landmark is needed special processing, perhaps do not merge.

Step 4: the merging process of BUILDINGS MODELS is organized into a level merges tree and express;

Step 5: level is merged each non-root node of setting, the process that merges is expressed as some easy operation operators;

Step 6: operation operator is encoded, and be concatenated into continuous code stream;

Step 7: the minimum direction of each building is surrounded the polygon box carry out geometry compression and coding;

Step 8: the code stream in step 7 and the step 6 is spliced, form total code stream.

The present invention can be applicable to large-scale city roaming system.

Beneficial effect: advantage of the present invention is: the urban architecture model scene of a complexity can be expressed as the code stream form of the compression of a series of layerings, and every layer data stream is much smaller than original model data amount, thereby has reduced the memory data output of scene.

Figure of description

The building data structure diagram of Fig. 1 city of the invention process display system;

The structure of Fig. 2 city scene BUILDINGS MODELS data;

The oriented bounding box of the single building of Fig. 3;

The polygon bounding box that the level of a plurality of buildings of Fig. 4 merges;

Fig. 5 BUILDINGS MODELS is the process of progressive code stream through compression expression.

Embodiment

Particular content in conjunction with the inventive method provides following examples:

The contextual data that this implements employed three-dimensional city BUILDINGS MODELS is so-and-so regional economy development area, Zhejiang comprises more than 17000 BUILDINGS MODELS in 4 square kilometres of scopes.

The equipment of operation the inventive method is ordinary individual's computing machine, and its concrete configuration is Pentium 2.7G, 1G internal memory, 160G hard disk.Software platform is Windows XP.

Concrete performance is as follows:

Step 1: model of place is classified, comprise road, border, sub-district, types such as building node and terrestrial reference;

Step 2: the merge order that calculates each BUILDINGS MODELS; Calculate by following formula

$d(P,Q)=\frac{\mathrm{Area}\left(P\right)\·\mathrm{Area}\left(Q\right)}{{\left(\mathrm{Area}(P\∪Q)\right)}^{\mathrm{\α}}}{d}_H(P,Q)$

Wherein selecting α is 2;

Step 3: merging process is carried out encoded recording;

Step 4: the code stream after will encoding is stored on the computer server;

Step 5: utilize the computer drawing means, on computer screen, show the three-dimensional city scene:

(1) receives elementary stream from server, the basic layer of displayed scene;

(2) receive the first levels of detail code stream from server, the ground floor information of displayed scene, scene is more complicated;

(3) receive the second levels of detail code stream from server, the second layer information of displayed scene, scene is more complicated;

(4) by that analogy, up to receive all levels of detail code streams from server, the whole scene demonstration finishes.

At last, it is also to be noted that what more than enumerate only is specific embodiments of the invention.Obviously, the invention is not restricted to the foregoing description, can also many operative combination.The all scenario that those of ordinary skill in the art can directly derive or associate from content disclosed by the invention all should be thought protection scope of the present invention.

Claims (3)

1. the progressive compression and the transmission method of a urban architecture model, this method is a kind of method based on the building geological information, it is decomposed into a series of compact packed data stream of expressing with the geometric model of City Building, it is characterized in that: with progressive mode the building geometric model is compressed and transmits, it comprises the steps:

(1) the three-dimensional city model is classified, be divided into road, border, sub-district, building node and terrestrial reference;

(2), obtain its minimum direction polygon bounding box and distance to each BUILDINGS MODELS;

The distance metric of two buildingss is the distance of its minimum polygon bounding box, is defined as follows:

$d(P,Q)=\min \{\frac{\mathrm{Area}\left(P\right)\·\mathrm{Area}\left(Q\right)}{{\left(\mathrm{Area}(P\∪Q)\right)}^{\mathrm{\α}}}\·d(x,y)|x\∈P,y\∈Q\}$

P in the formula, Q are the minimum polygon bounding box of 2 buildings, and Area (P) is the area of P in the projection on ground, and Area (Q) is the area of Q in the projection on ground, Area (P _UQ) be P and the Q area in the projection of ground common factor part, α is the distance calculation parameter greater than 0, and (x y) is two some x, the distance between the y to d;

(3) volume by the minimum bounding box of each BUILDINGS MODELS calculates their merge order from small to large;

(4) merging process is carried out encoded recording;

BUILDINGS MODELS is carried out the union operation of level, specifically comprises:

A, the BUILDINGS MODELS that belongs to same sub-district is merged according to building orientation, distance, orientation, information;

B, to different districts, if they are not in the both sides of road, merge according to distance, the azimuth information of sub-district;

C, in each merging process, keep boundary information;

D, in each merging process, some landmark is needed special processing, perhaps do not merge;

(5) code stream after will encoding is stored on the computer server;

(6) from server, constantly obtain code stream, utilize the computer drawing means, demonstration three-dimensional city scene from coarse to fine on computer screen.

2. the progressive compression and the transmission method of a kind of urban architecture model according to claim 1, the parameter alpha that it is characterized in that distance calculation is between the 1-3.

3. the progressive compression and the transmission method of a kind of urban architecture model according to claim 2, the parameter alpha that it is characterized in that distance calculation is 2.

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