ArcGIS Tutorial: 3D Polygon Features

　　What are 3D polygon features?

A polygon feature is a GIS object whose geographic representation (a series of x-and y-coordinate pairs for enclosing areas) is stored in a row of the database as one of its properties (or fields). Polygon features have two separate parts that may be used for modeling in 3D mode: their outer perimeter lines and inner areas. In almost all instances, polygons should be modeled as 3D features only if the outer perimeter needs to include Z-values or heights in order to correctly position itself in 3D space.

If you need to model a 3D collision in the inner area of the opposite side, you can only use Multipatch features or feature polygons (such as tins) to meet the overwhelming majority of usage. This is because the surface of a 3D polygon is calculated in a consistent manner only when there are exactly three vertices (construct 3D triangles) or when vertices represent planes. Because 3D polygons meet these requirements with high labor intensity, they are not recommended as a workflow to maintain 3D area polygons.

3D Polygon features store z-coordinates in a geometric or Shape field that embeds z-coordinates into their feature class. This means that each new vertex created for a 3D polygon automatically contains z-values, allowing its perimeter to connect any two points together-whether they are on the ground, above the ground, or below the ground.

Examples of 3D polygon features are typically related to areas that define surfaces. Examples include the following:

Lake border;

Building cover area;

Street Roadside Line

Although you can also use a numeric feature attribute opposite Z-values to model, this option displays all features with the same z-coordinate in the entire polygon and may not support all the same analysis and interaction options supported by embedded Z-values. However, in some cases, a planar definition that defines a planar height based on an attribute may actually be a suitable design, such as when it is merged with an extrude or used to represent vertical parcel ownership in a multi-storey building.

All features that are only on the elevation surface, such as administrative boundaries, areas of interest, and parcel boundaries, should always be modeled as 2D polygon features. This simplifies the data storage and maintenance operations of the features and enables the features to automatically adjust the height when the underlying surface data is improved. In addition, if these polygons require Z-values, you can use tools such as interpolation Shape to calculate the Z-values of features by referencing the elevation data.

　　Two ways to create a 3D polygon feature class

There are two main ways to create a 3D Polygon feature class: Create a new Polygon feature class or convert existing 2D polygon data to a new feature class that contains Z-values.

　What should the z-value indicate?

Z-values are primarily used to include elevations in GIS features. These values can represent absolute heights (such as the aircraft at 30,000 feet) or height relative to the ground (for example, a subway station located 50 metres below the ground). Both methods are fully supported when displaying and analyzing a generated 3D feature class.

It is important to note that Z-values can also be used to include other vertical measurements, such as air pollution observations, temperatures, and other measurements for surface generation. Creatively applying Z-values and what they represent are useful for understanding and analyzing data.

The units and planes of the feature class Z-values should be defined in the feature dataset where the feature class resides, if it exists, or in the feature class itself (if there is no feature dataset). If no units are defined, ArcGIS assumes that the units of Z are consistent with the units of XY. This assumption can be problematic, especially if the XY unit is a geographic unit (latitude/longitude).

　　Creating 3D Polygon Features

You can create 3D features interactively in the geoprocessing framework using standard ArcGIS editing frameworks in ArcMap, ArcGlobe, and ArcScene, or with tools that include Z-values in the output. There are some specific behaviors to be aware of when creating and editing polygons in the 3D view.

ArcGIS Tutorial: 3D Polygon Features