Analysis of ArcGIS polytopic (multipatch) -- Introduction

The multipatch structure is a data structure parallel to points, lines, and surfaces in ArcGIS data structure. It is a core structure for ArcGIS 3D, arcGIS platform can flexibly describe rules and irregular 3D entities. For relative rule models such as buildings and roads, ArcGIS can be expressed in the GIS platform, and other GIS platforms can also. However, for geological strata with irregular structures, a node-level 3D model is required, many GIS systems can only be displayed in the form of three-dimensional point symbols. The disadvantage of this method is that node-level generation, management, editing, and analysis cannot be performed. ArcGIS can do this simply because of the polygon data structure.

Maybe we usually do not involve polygon when doing two-dimensional projects, but once it involves three-dimensional applications, especially when we need to describe irregular structures such as strata based on the truth, we need to study the polygon structure in depth. As mentioned above, the polygon of ArcGIS can be operated at the node level. That is to say, each node in ArcGIS can be generated, queried, modified, and so on, but it does not mean that the coordinates of each node for which the polygon must be generated are calculated (although the interface allows this ). ArcGIS generates a polygon automatically/manually divided into the following three methods: the first two are relatively automated, the third is manual, and manual intervention is powerful:

1) tool import method, that is, ArcGIS toolbox has the import 3D files tool, you can directly convert 3DS, Flt, fig, SKP, Dae and other third-party models into a polygon. The cityengine modeling project can also be directly exported as a polygon. This is the core step for transferring models from a non-GIS platform to a GIS platform. This method is often used for building and road models in 3D cities.

2) It is automatically generated using ArcGIS tools. This method uses multiple tools (buffer 3D, Intersect 3D, extrude between, etc.) for layer 3D to feature class and 3D space calculation in toolbox) based on the existing 3D GIS layers or data, spatial operations are performed to automatically solve the new polygon data. This process is the same as above and does not require human intervention at the node level. The ArcGIS tool handles the process on its own. In this process, the common scenario is to use a three-dimensional pipeline to generate a three-dimensional pipeline polygon. Spatial analysis is used to solve the intersection of the two polygon (whether the radar scanning range and the flight track of the plane are intersecting, geological mass profile analysis ).

3) a polygon must be generated at the node level. The development interface organizes ordered nodes to generate triangles (the most common is triangles), and then concatenates them into polygons. This method is mainly used to generate irregular 3D models, such as complex geological bodies. Geological, subway, and other industries need to carry out 3D simulation of irregular shape objects such as strata and minerals.

In the first two cases, you generally do not need to understand the internal structure of the polygon, but you only need to use the corresponding interface to automatically generate the polygon. However, in the third case, in order to let us "Know where it is ", I will use several blogs to parse the internal structure of a polygon.

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