What are the ways to get a 3d model?

Data acquisition is the basis of three-dimensional modeling, which is currently applied to the acquisition methods of building attribute data and texture data, digital ground and elevation, and natural landforms. There are mainly three-dimensional laser scanning to obtain data, aerial photogrammetry technology to obtain data, and mobile mapping system to obtain data.

1. 1 Use 3D laser scanning to obtain data.

Three-dimensional laser scanning system is also called three-dimensional laser mapping system. It is mainly composed of three-dimensional laser scanner and system software. The system can quickly, conveniently and accurately carry out close-range mapping of static objects, obtain fine three-dimensional coordinates in space, and provide high-precision data for three-dimensional modeling. Three-dimensional laser scanning system is mainly used to obtain three-dimensional data in a small area.

1.2 using aerial photogrammetry technology to obtain data

The data acquisition of aerial images is to process and synthesize the data by loading camera platforms, such as digital aerial cameras and lidar image measurement systems, to obtain digital line vector diagram (DLG) and digital elevation model (DEM), and to establish spatial three-dimensional data such as digital orthophoto map (DOM). It is suitable for macro and large-area acquisition of spatial three-dimensional data.

1.3 using mobile surveying and mapping system to obtain data

Mobile surveying and mapping system is a comprehensive multi-sensor surveying and mapping system based on automobile, which is mainly composed of GPS receiver, inertial navigation system, CCD camera, lidar rangefinder and vehicle-mounted platform. The characteristic of the system is that it can make up for the shortcomings of aerial photogrammetry technology that it is difficult to provide comprehensive detailed information of complex ground objects and the slow time to obtain ground data manually. It is suitable for data acquisition of three-dimensional spatial information with medium area and high accuracy.

2 key technologies of 3D modeling data processing

2. 1 model file format

Because it is necessary to redraw the 3D model in real time in the process of urban 3D modeling, texture mapping is generally used to improve the fidelity instead of increasing the complexity of geometric modeling.

In various projects, most 3D models are in OpenFlight format. OpenFlight format is the most popular file format in the field of virtual reality and the industry standard of facts. OpenFlight uses geometric hierarchy and node attributes to describe three-dimensional objects. Node types are database header (db), group, object and polygon from high to low. Group nodes can include sub-group nodes and object nodes. For each object, its model entity consists of one or more faces, and each face is calibrated by multiple vertices. The geometric modeling of model entities is determined by these points and surfaces, and the texture of model entities is realized by texture mapping.

2.2 Model structure

According to the demand of 3D model to express urban information, considering that the model needs to be updated with the pace of urban development and construction, in order to adapt to this actual situation, we divide the regional scene of 3D model into two parts: basic environment and ground features, and all kinds of land parcels and road models are classified into the basic environment scene part, while the ground building models at all levels with relatively frequent updates are classified into the ground features part. In modeling, each object that needs real-time query specifies its own identity. This structure can not only meet the functional requirements, but also bring convenience for future data update and maintenance.