3D MODELLING

3D Modelling



3D Modelling

Introduction

Three-dimensional modeling involves the use of modern graphics hardware to present spatial data in three dimensions and allow the user to interact with the data in real time. When applied to geographic applications, this enables the user to view map data that include height information in a more intuitive and comprehensible form, rather than using a projection of those data onto a 2D plane (Rhyne, 2007). For example, Figure 1 illustrates a terrain elevation model that is displayed as a 3D surface, with satellite imagery mapped onto that surface and 3D building models overlaid on the terrain. The user is then free to view the scene from any vantage point or create a fly-through of the scene where a path is navigated through the 3D world.

A GIS application that utilizes 3D modeling will typically provide the functionality of a standard GIS system—such as the ability to display different layers of data and perform analyses on the terrain surface—in addition to being able to display the layers within a 3D context where the user can manipulate the viewpoint interactively (Luebke, 2002). This involves a synergy of multiple disciplines, including real-time 3D graphics, visual simulation, GIS, CAD, and remote sensing. The remainder of this entry provides further details about the common features of 3D modeling systems, describes the creation of 3D terrain and symbols, and concludes with some background about the graphics technology used to create the 3D images (Luebke, 2002).

What Is Required From a 3D Modelling

GIS acquire, manage, maintain, analyze, and visualize spatial data. This section describes how well commercial GIS in general currently are able to meet these requirements for a fully functional 3D GIS.

Data Acquisition

Satellite remote sensing, terrestrial data acquisition (e.g., surveying), and map-based data capture (e.g., digitizing elevation data) have traditionally been used to acquire 3D terrain data. Well logging and measurements taken in vertical columns in the ocean are also sources of 3D data. More recently, radiometry using RADAR and LiDAR (laser scanning) is now being widely used to create 3D data, particularly of buildings and other structures (Hearnshaw, 2006).

Image analysis has long been used to extract elevation and height data from satellite and airborne images. Image classification tools can detect and classify the roofs of buildings and distinguish between planar concrete areas (e.g., parking lots) and buildings. Since the length of the shadow indicates the height of a building, if it is possible to measure the shadow length reliably, it is possible to make solid estimations on the height of a building. The potential from automating these methods is huge, since it enables the automated extraction of building height information from any traditional 2D satellite image (Abdul Rahman, 2006).

In summary, 3D data are becoming more and more available (e.g., by terrestrial 3D scanning systems) in high accuracy, and automated techniques for extracting height and elevation information from traditional 2D sources are being developed. In this regard, the requirements of a 3D GIS are met.

Data Modeling and Management

With respect to the storage, management, ...