CN110751696A

CN110751696A - Method, device, equipment and medium for converting BIM (building information modeling) model data into glTF (glTF) data

Info

Publication number: CN110751696A
Application number: CN201911351939.1A
Authority: CN
Inventors: 毛飞; 马礼伟
Original assignee: Glodon Polytron Technologies Inc
Current assignee: Glodon Polytron Technologies Inc; Glodon Co Ltd
Priority date: 2019-12-25
Filing date: 2019-12-25
Publication date: 2020-02-04
Anticipated expiration: 2039-12-25
Also published as: CN110751696B

Abstract

The invention discloses a method and a related device for converting BIM model data into glTF data, which are used for solving the problems of low MD data format loading capability and poor expansibility in the light weight process of the existing three-dimensional model. The method for converting the BIM model data into the glTF data mainly comprises the following steps: 1) uploading the three-dimensional model file to a cloud platform, and converting the three-dimensional model file into MD data; 2) converting the MD data into glTF data, which specifically comprises the following steps: exporting scene; analyzing the node; exporting material; and exporting the mesh. After the conversion into the glTF format, the user can directly import the data without creating redundant importers, loaders and converters. Meanwhile, because the glTF data is in a json format, the analysis and loading speed is high, and the extension can be conveniently carried out.

Description

Method, device, equipment and medium for converting BIM (building information modeling) model data into glTF (glTF) data

Technical Field

The invention belongs to the technical field of BIM (building Information modeling), and particularly relates to lightweight conversion and glTF data conversion of a three-dimensional model.

Background

With the development of cloud technology, more and more applications are moving to the Web side, and users can conveniently use the applications through Web pages or mobile phones. The three-dimensional model lightweight application generally comprises three parts of model data conversion, Web end rendering and model data consumption. The model conversion extracts light-weight geometric data and an MD data format for secondary consumption from a huge BIM original model, greatly compresses the data size of the model, and lays a foundation for Web end display and editing. The Web end rendering is mainly used for rendering geometric data such as points, lines and planes and presenting the geometric data to a user. However, there are some drawbacks to be solved after converting the BIM model into the MD data format. Such as its data loading performance, to be improved. The scene data analysis and the 3D geometric data are converted into a format required by a graphic API, and the 3D data are transmitted into the GPU and then the graphic API is called to draw. If the data format can be arranged with reference to the data format in the GPU interface, the loading speed can be greatly increased. And the MD data format is not a universal 3D model format, the expansibility is not strong, and a user needs to create an importer, a loader and a converter when using the format, so the expansibility needs to be improved.

The invention relates to the following technical terms:

bimface: the BIM application development platform of the Guangda company is the same as BIM360 and BIMglue of the Autodesk company, and can enable researchers in the construction industry to carry out secondary development, so that more diversified BIM application is provided for users.

Md (modeldrive): the lightweight data format used by the Bimface model display is an intermediate format for three-dimensional model conversion, and mainly comprises scene, symbol, mesh, material and texture. Wherein:

scene: consists of nodes (nodes) of the following types:

groupnode (composite node): combined node

Meshnode (mesh node): mesh can be shared between mesh

Geotrynode (geometric node): there are several types of parametrically described nodes: pipe, box, tube

Symbol instancenode (type instance node): instance nodes of Symbol (type) for node level, sharing of complex primitives

Symbol (type): a general term for a certain type of grid data is usually combined with a matrix for grid data reuse

mesh (mesh): is composed of a series of polygons, and each polygon has three component values of x, y and z at its vertex

material (material): for describing the appearance of the grid

texture: chartlet of grid surface

glTF (Graphics Library Transmission Format): the method is a runtime resource format for GL (Open graphics library Open GL, embedded system Open graphics library Open GL ES and Web graphics library Web GL) interfaces, and has the advantages of high efficiency, easiness in expansion, capability of cooperation and the like in transmission and loading of 3D data. At present, a mainstream three-dimensional model data format is designed aiming at data production, and cannot meet the requirement of internet development in transmission and content analysis, and a glTF format is characterized in that aiming at efficient transmission and analysis, an extensible and universal release format is defined for a 3D content production tool and service, the glTF is transmitted in a binary (Array Buffer) mode, and is very efficient, and meanwhile, in order to improve the analysis efficiency, a data body of the glTF is designed into a form that Web GL can be directly loaded.

Accesser (Accessor): all data with large data volume including multi-grid messages, multi-skin skins and multi-animation interactions are stored in the cache, and the access reads corresponding data according to the access Id.

bufferView (buffer view): and pointing to a view of a certain cache, wherein the cache corresponding to one buffer View is a subset of the whole cache.

buffer (buffer): binary data streams pointing to geometry, animation, skin.

primary geometry (raw geometry): geometry data, including texture information rendered together.

GL (Graphics Library): the underlying graphics libraries WebGL, OpenGL ES and OpenGL are collectively referred to.

JSON (Java Script Object Notation): java Script object markup language.

Disclosure of Invention

The invention aims to solve the problems of low MD data format loading capability and weak expansibility in the existing three-dimensional model lightweight process.

In order to achieve the above object, the present invention provides a method for converting BIM model data into glTF data, comprising the steps of:

1) uploading the three-dimensional model file to a cloud platform, and converting the three-dimensional model file into MD data, wherein the MD data comprises scene, grid mesh, material and texture, the scene consists of nodes, and the nodes comprise the following types: combining nodes, namely a group node, a grid node, a geometry node and a type instance node, namely a symbol instancenode;

2) converting the MD data into glTF data, which specifically comprises the following steps: deriving a scene; analyzing the node; exporting material; and exporting the mesh.

Further, the deriving the scene specifically includes: and creating a new scene node, wherein the id is set to the id value of the scene in the MD data, thereby realizing the derivation of the scene information from the MD data.

Further, the parsing the node specifically includes: traversing all the nodes in the scene of MD data, firstly judging which node is, if the node is a geometric node geotreynode, constructing mesh data according to geometric parameters for subsequent use, if the node is a grid node or a type instance node SymbolInstancenode, acquiring corresponding grid mesh data for subsequent use, and if the node is a combined node groupnode, continuously traversing child nodes of the node.

Further, the deriving the material specifically includes: texture attributes pbrmmetalicrroughhness in the glTF data format are used to describe texture in MD data, and texture maps in the glTF data format are used to describe maps in MD data.

Further, the deriving the mesh specifically includes: the mesh data analyzed by the node analyzing step and the texture data derived by the texture deriving step are described as original geometric data primitives array form, each original geometric data primitive specifies one or more attributes, and each original geometric data primitive specifies texture material and type mode.

The invention also provides a device for converting the BIM model data into the glTF data, which comprises:

the MD data generation module is used for uploading the three-dimensional model file to a cloud platform and converting the three-dimensional model file into MD data, the MD data comprises scene, grid mesh, material and texture, the scene is composed of nodes, and the nodes comprise the following types: combining nodes, namely a group node, a grid node, a geometry node and a type instance node, namely a symbol instancenode;

the glTF data conversion module is used for converting the MD data into the glTF data, and specifically comprises the following steps: a scene derivation submodule; a node analysis submodule; a material export submodule; and a grid mesh derivation submodule.

Further, the scene derivation sub-module is configured to: and creating a new scene node, and setting id as the id value of the scene in the MD data, thereby realizing the derivation of the scene information from the MD data.

Further, the node parsing submodule is configured to: traversing all the nodes in the scene of MD data, firstly judging which node is, if the node is a geometric node geotreynode, constructing grid mesh data according to geometric parameters for subsequent use, if the node is a grid node or a type instance node SymbolInstancenode, acquiring corresponding grid mesh data for subsequent use, and if the node is a combined node groupnode, continuously traversing child nodes of the node.

Further, the material export sub-module is configured to: texture attributes pbrmmetalicrroughhness in the glTF data format are used to describe texture in MD data, and texture maps in the glTF data format are used to describe maps in MD data.

Further, the mesh derivation submodule is configured to: the method comprises the steps of describing mesh data analyzed by a node analysis submodule and material data exported by a material export submodule into an original geometric data primitive array form, wherein each original geometric data primitive specifies one or more attribute attributes, and each original geometric data primitive specifies a material and a type mode.

The present invention also provides an electronic device, including: a storage device; one or more processors; wherein the storage is configured to store one or more programs that, when executed by the one or more processors, cause the one or more processors to implement the aforementioned methods.

The present invention also provides a computer-readable storage medium having stored thereon a computer program which, when executed, implements the aforementioned method.

Compared with the prior art, the method has the advantages that after the BIM is converted into the MD data format, the MD data format is further converted into the GLTF format, and a user can directly import the data without creating redundant importers, loaders and converters. Meanwhile, because the glTF data is in a json format, the analysis and loading speed is high, and the extension can be conveniently carried out.

Drawings

FIG. 1 is a schematic diagram of the MD data format;

FIG. 2 is a schematic diagram of the configuration of the glTF data format;

FIG. 3 is a flow chart of a method of data conversion according to the present invention;

FIG. 4 is a view showing the structure of the apparatus of the present invention.

Detailed Description

In order to facilitate the understanding and implementation of the present invention for those of ordinary skill in the art, the following technical solutions of the present invention are clearly and completely described with reference to the accompanying drawings, and it should be understood that the described embodiments are only for the purpose of explaining the present invention and do not limit the present invention.

The invention firstly performs lightweight conversion on the three-dimensional model, converts the BIM into the MD data format, and then performs glTF data conversion on the basis to generate the data format which is easy to analyze, load and render. The invention adopts Microsoft.glTF.CPP to encode and generate a glTF format file, and the underlying JSON encoding depends on rapidjson.temprelease (a third-party library which can rapidly analyze and generate JSON data).

The scheme of the present invention is specifically described below.

Firstly, any model file is converted into lightweight MD data after being uploaded to a Bimface cloud platform. The website of the Bimface cloud platform is http:// Bimface. com/. The MD data format is mainly composed of scene, symbol, mesh, material, and texture as shown in fig. 1.

Then, the MD data is further converted into data in the glTF format.

The construction of the glTF formatted data and its significant advantages will be explained first. As shown in fig. 2, the glTF formatted data includes three parts: json formatted file (. gltf), binary file (. bin), picture file (. jpg. png). The json formatted file (. gltf) contains complete description of the scene, including node hierarchical relationship, camera, and material. The binary file (. bin) contains geometry data, animation data, skin data, and other cache-based data. The picture file (.jpg. png) is used for mapping.

The json file is the core part of the glTF, and describes the structure and components of a three-dimensional model scene. The main elements that make up this document include the following: the basic structure of scene, the mesh of three-dimensional objects appearing in the scene, the index information of the three-dimensional object data, and the related information of how the objects should be rendered. The elements describing the basic structure of the scene mainly comprise multi-scene scenes, multi-node nodes, multi-camera cameras and multi-animation; the elements describing the three-dimensional objects appearing in the scene mainly comprise multi-grid meshes, multi-texture texturs, multi-image, multi-sample samplers and multi-skin skins; the elements of the data information comprise buffers, buffers and registers; elements of rendered related information are multi-material materials, multi-technology queries, multi-program programs, and multi-shading shaders. The elements are stored in the file in the form of a dictionary, and the elements are associated with each other through IDs. The JSON file also uses URLs to implement references to external files, such as bin files, image files, which store scene data. All information describing the whole scene is completely described by the association and the reference in the two forms.

The glTF format is used for 3D model data representation, with several significant advantages:

1. and (3) reducing the data volume: the data in the glTF format is compact, and json coding is easy to analyze. Geometry and animation containing a large amount of data are saved in a binary form, and the data amount is greatly reduced.

2. And (3) quick loading: the glTF data structure is designed according to the data form of the GPU graphics interface so that the glTF data can be directly loaded into the GPU cache. Only a simple copy operation is required and no parsing or further processing is required. For example, binary data describing a grid may be viewed as a JavaScript array, which may be loaded directly into the GPU cache. This process involves only a simple copy of the data and no parsing of the data or further processing of the data.

3. Full 3D scene description: the glTF provides a complete description of the 3D scene, and the entire scene (including nodes, transforms, transform hierarchies, surfaces, textures, cameras, animations) can be easily derived and provided as data to downstream programs for use.

The scheme for converting the MD data into the data in the glTF format specifically includes deriving a scene, a node parsing node, deriving a material, and deriving a mesh, which are respectively described in detail below. FIG. 3 depicts a flow of steps for an embodiment of the present invention.

Deriving scene

The glTF creates a new scene node, and id is set as the id value of the scene in the MD data, so that scene information can be derived from the MD data.

Resolving a node

A scene in MD data is composed of nodes, and the nodes can be divided into 4 types according to types:

groupnode (composite node): several child nodes may be included under the node. The id of the child node comprises two parts, wherein the prefix is the id of the parent node, and the suffix is different characters arranged according to the sequence of the child node. The parent node itself may maintain a transformation matrix that maintains the offset, rotation, and scaling information for that node. The child nodes may be mesh nodes, geometry nodes, and even type instance nodes, symbol instancenodes. Since the child node is a reference to the other node, there is no need to create a mesh at this time.

(mesh node): pointing to an actual mesh, it itself holds a transformation matrix that holds the offset, rotation and scaling information for that node. The mesh node mesh does not need to create a mesh.

(geometric nodes): it may be a box, pipe or tube. For the box, 8 vertices can be obtained to form 12 triangles in turn, and then a normal vector is obtained. For the more complex tubes Pipe and tube, vertex data can be obtained through uniform sampling, and then vertex indexes and triangular surface patches are constructed, and normal vectors are calculated.

(type instance node): an actual node is referenced, and the referenced node may be referenced multiple times. The method has the advantages that a transformation matrix can be stored, and the effect is that only one matrix needs to be added without adding the geometric data of the original node if the same node exists. The id of each symbol is different, the prefix is the id of the node actually referenced, and the suffix is arranged with different characters in the adding order of the symbol instance nodes. Because the node refers to other nodes, the node does not need to create the mesh, and can directly find the corresponding mesh according to the id.

The analysis in this step is to traverse all nodes in the MD data scene, determine which node is, if the node is a non-reference type node geometric node, construct grid mesh data according to geometric parameters for deriving grid mesh in the subsequent fourth step, and if the node is a reference type node group node, grid node mesh or type instance node symbol, construct grid mesh data is not needed, and the derivation of grid mesh in the fourth step can be performed only by acquiring corresponding grid mesh data. The step is essentially to prepare the mesh data and prepare for deriving the mesh in the fourth step.

Exporting material

The glTF uses a set of parameters based on physical rendering to define the material, and this material presentation scheme enables the glTF file to be rendered on different platforms.

For the material in the MD data, the material attribute pbrmmetalicroughress description in the glTF formatted data can be used to derive the material in the MD data.

Taking the data structure defined below as an example, baseColorFactor represents the color of a material, metalllicFactor represents the metal characteristics of a material, and roughnessFactor represents the roughness of a material. The use attribute doubllesided may be used to control whether to display on both sides.

For the map in the MD data, the texture map of the glTF format data can be used for description, so as to derive the map in the MD data. In the mapping conversion, two attributes, normal and emissiveFactor in the glTF texture mapping are used to describe the mapping in the MD data. normaltfuture is used to describe the texture of the map, and emissiveFactor is used to control the color and intensity of light reflected from the material. See the data structure defined as follows:

4. export mesh

After the node is analyzed in the step 2, mesh data including a vertex, an index, a normal vector and a material uv coordinate are prepared. After the texture material is exported in step 3, the texture data is prepared. The step leads the mesh data and the material data of the grids into a glTF file.

In the glTF format, the mesh is described as the primary geometry data primitives array form, and the step of deriving the mesh is to describe the mesh data obtained by the step 2 and the step 3 derived material data as the primary geometry data primitives array form. The original geometric data primitives point to data needed by GPU drawing, wherein a plurality of attribute attributes can be specified, and the attribute attributes correspond to vertex data needed by the GPU drawing. Meanwhile, each original geometric data prime also specifies a material and a type mode of the original geometric data prime, and the mode =4(TRIANGLES) is used in the invention.

The data structure of the mesh is described below, and the original geometry data priority array contains an original geometry data priority. Three attributes in the multi-attribute attributes respectively represent normal vectors, vertexes and uv coordinates of the material, and the specific meanings are shown in table 1. indices denotes a vertex index. Material represents material. mode represents a type. The corresponding number following represents the accesorid.

TABLE 1

The data structure defined below describes that one accessor access corresponds to one buffer view bufferView, and byteOffset and count respectively represent the location and size of data in the buffer view bufferView. The componentType represents a data type, data of different data types occupy different numbers of bytes, and the type represents the number of elements. The detailed meaning of componentType and type is described in table 2, such as VEC3 containing 3 data elements.

TABLE 2

As shown in fig. 4, an embodiment of the present invention further provides an apparatus for converting BIM model data into glTF data, including:

Preferably, the scene derivation submodule is configured to: and creating a new scene node, wherein the id is set to the id value of the scene in the MD data, thereby realizing the derivation of the scene information from the MD data.

Preferably, the node resolution submodule is configured to: traversing all nodes in an MD data scene, firstly judging which node is the node, if the node is a geometric node geotreynode, constructing grid mesh data according to geometric parameters for subsequent use, if the node is the grid node or a type instance node SymbolInstancenode, acquiring corresponding grid mesh data for subsequent use, and if the node is a combined node groupnode, continuously traversing child nodes of the node.

Preferably, the material derivation sub-module is configured to: texture attributes pbrmmetalicrroughhness in the glTF data format are used to describe texture in MD data, and texture maps in the glTF data format are used to describe maps in MD data.

Preferably, the mesh derivation submodule is configured to: the method comprises the steps of describing mesh data analyzed by a node analysis submodule and material data exported by a material export submodule into an original geometric data primitive array form, wherein each original geometric data primitive specifies one or more attribute attributes, and each original geometric data primitive specifies a material and a type mode.

It is clear to those skilled in the art that the specific working processes of the modules correspond to the steps of the foregoing method embodiments, respectively.

The embodiment of the invention also discloses an electronic device, which comprises: a storage device; one or more processors; wherein the storage is used to store one or more programs which, when executed by the one or more processors, cause the one or more processors to implement the methods of the foregoing embodiments.

The present invention also provides a computer-readable storage medium having stored thereon a computer program which, when executed, implements the method of the aforementioned embodiments of the present invention.

In conclusion, after the BIM is converted into the MD data format, the MD data is further converted into the glTF format with faster loading and stronger expansibility, so that the loading speed is increased, and the expansibility is enhanced. The reason that the loading of the glTF data is faster is that the glTF data structure is designed according to the GPU interface data format as much as possible, thereby reducing the loading time. The reason that the extensibility of the glTF data is higher is that the initial glTF standard provides a rich feature set, which provides a possibility for the extension of the glTF data. Meanwhile, the glTF defines a set of mechanisms that support the extension of reservation for general and specific providers.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, and the scope of the invention should not be limited to the embodiments described above.

Claims

1. A method for converting BIM model data into glTF data, comprising the steps of: 1) Uploading the three-dimensional model file to a cloud platform, and converting the three-dimensional model file into MD data, wherein the MD data comprises scene, grid mesh, material and texture, the scene consists of nodes, and the nodes comprise the following types: combining nodes, namely a group node, a grid node, a geometry node and a type instance node, namely a symbol instancenode; 2) Converting the MD data into glTF data, which specifically comprises the following steps: deriving a scene; analyzing the node; exporting material; and exporting the mesh.

2. The method of claim 1, wherein the deriving the scene specifically comprises: and creating a new scene node, and setting id as the id value of the scene in the MD data, thereby realizing the derivation of the scene information from the MD data.

3. The method of claim 1, wherein the parsing the node specifically comprises: traversing all the nodes in the scene of MD data, firstly judging which node is, if the node is a geometric node geotreynode, constructing grid mesh data according to geometric parameters for subsequent use, if the node is a grid node or a type instance node SymbolInstancenode, acquiring corresponding grid mesh data for subsequent use, and if the node is a combined node groupnode, continuously traversing child nodes of the node.

4. The method of claim 1, wherein said deriving a material specifically comprises: texture attributes pbrmmetalicrroughhness in the glTF data format are used to describe texture in MD data, and texture maps in the glTF data format are used to describe maps in MD data.

5. The method of claim 1, wherein said deriving a mesh specifically comprises: the mesh data analyzed by the node analyzing step and the texture data derived by the texture deriving step are described as original geometric data prime array forms, each original geometric data prime specifies one or more attributes, and each original geometric data prime specifies texture material and type mode.

6. An apparatus for converting BIM data into glTF data, comprising: the MD data generation module is used for uploading the three-dimensional model file to a cloud platform and converting the three-dimensional model file into MD data, the MD data comprises scene, grid mesh, material and texture, the scene is composed of nodes, and the nodes comprise the following types: combining nodes, namely a group node, a grid node, a geometry node and a type instance node, namely a symbol instancenode; the glTF data conversion module is used for converting the MD data into the glTF data, and specifically comprises the following steps: a scene derivation submodule; a node analysis submodule; a material export submodule; and a grid mesh derivation submodule.

7. The apparatus of claim 6, wherein the scene derivation sub-module is to: and creating a new scene node, and setting id as the id value of the scene in the MD data, thereby realizing the derivation of the scene information from the MD data.

8. The apparatus of claim 6, wherein the node resolution submodule is to: traversing all the nodes in the scene of MD data, firstly judging which node is, if the node is a geometric node geotreynode, constructing grid mesh data according to geometric parameters for subsequent use, if the node is a grid node or a type instance node SymbolInstancenode, acquiring corresponding grid mesh data for subsequent use, and if the node is a combined node groupnode, continuously traversing child nodes of the node.

9. The apparatus of claim 6, wherein the material derivation sub-module is to: texture attributes pbrmmetalicrroughhness in the glTF data format are used to describe texture in MD data, and texture maps in the glTF data format are used to describe maps in MD data.

10. The apparatus of claim 6, wherein the mesh derivation submodule is to: the method comprises the steps of describing mesh data analyzed by a node analysis submodule and material data exported by a material export submodule into an original geometric data prime array form, wherein each original geometric data prime specifies one or more attribute attributes, and each original geometric data prime specifies a material and a type mode.

11. An electronic device, comprising: a storage device; one or more processors; wherein the storage is to store one or more programs that, when executed by the one or more processors, cause the one or more processors to implement the method of any of claims 1-5.

12. A computer-readable storage medium, on which a computer program is stored which, when executed, implements the method of any of claims 1-5.