3D polygon features
What are 3D polygon features?
A polygon feature is a GIS object that stores its geographic representation—a series of x and y coordinate pairs that enclose an area—as one of its properties (or fields) in the row in the database. Polygon features have two separate parts that can potentially be modeled in 3D: their exterior perimeter line and their interior area. In nearly all instances, polygons should be modeled as 3D features only when the exterior perimeter needs to include z-values, or heights, to correctly locate itself in 3D space.
If you need to model the 3D bumpiness of the interior area of a polygon, the vast majority of use cases can only be met using multipatch features or a functional surface (such as a TIN). This is because the surface of a 3D polygon can only be guaranteed to be calculated in a consistent manner when there are exactly three vertices (constructing a 3D triangle), or when the vertices represent a planar surface. The level of effort necessary for 3D polygons to meet these requirements is high, and therefore they are not recommended as a workflow for maintaining 3D areal faces.
3D polygon features store z-coordinates embedded inside their feature geometry, or Shape field, of their feature class. This means that z-values are automatically included with every new vertex created for the 3D polygon, allowing its perimeter to connect any two points together—regardless of whether they are on, above, or below the ground.
Examples of 3D polygon features mostly relate to areas that help define a surface. Examples include:
- lake boundaries
- building footprints, and
- street curb lines
While it is also possible to model polygon z-values using a numeric feature attribute, this option will display the feature with the same z-coordinate for the entire polygon and may not support all the same analysis and interaction options supported with embedded z-values. However, in some cases, the definition of a flat polygon that defines its height from an attribute can actually be an appropriate design, such as when it is combined with extrusion and used to represent vertical parcel ownership inside multistory buildings.
Any features that live exclusively 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 of the features, and allows them to automatically adjust their heights if the underlying surface data improves. Also, if z-values are ever needed for these polygons, they can be calculated on to the features by referencing the elevation data and using tools such as Interpolate Shape.
Two ways to create a 3D polygon feature class?
There are two main ways to create a 3D polygon feature class: you can either create a brand new polygon feature class, or you can convert existing 2D polygon data into a new feature class that contains z-values.
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To create a new 3D polygon feature class: |
Check the Coordinates include Z values check box when defining the feature class's geometry. |
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To convert existing 2D data, there are multiple options available to set where the z-values can come from, including: |
Setting the height values from an elevation surface or using an existing feature attribute. Learn more about converting 2D features to 3D features  Tip:If using an attribute to set z-values for creating 3D polygons, every line will be effectively "flat", with all vertices sharing the same z-coordinate. |
What should the z-value represent?
Z-values are primarily used to include elevation in your GIS features. The values can represent absolute heights, such as an aircraft at 30,000 feet, or relative-to-ground heights, such as a subway station 50 meters below the surface of the ground. Both methods are fully supported in the display and analysis of the resulting 3D feature class.
It is worth noting that z-values can also be used for including other vertical measures such as air pollution observations, temperature, and other measures that are used in surface generation. Creative use of z-values, and what they represent, can be very useful in the understanding and analysis of your data.
The units and datum for a feature class's z-values should be defined on the containing feature dataset (if one exists) or on the feature class itself (if there is no feature dataset). If no units are defined, ArcGIS will assume that the Z units match the XY units. This assumption can be problematic, particularly if XY units are geographic (lat/long).
Creating 3D polygon features
3D features can be created interactively, using the standard ArcGIS editing framework in ArcMap, ArcGlobe, and ArcScene, or through the geoprocessing framework, using tools that incorporate z-values in the output. The creating and editing of polygons in a 3D view has some particular behaviors that you should be aware of. Learn more about editing polygons in 3D.