3D polyline features
What are 3D polyline features?
A line feature is a GIS object that stores its geographic representation—a series of x and y coordinate pairs—as one of its properties (or fields) in the row in the database. Some line features—such as underground subway lines—need to also include z-values, or heights, to correctly locate themselves in 3D space. These objects must be modeled as 3D line features.
3D line features embed their z-values inside the geometry, or Shape field, of their feature class. This means that z-values are automatically included with every new vertex created for the 3D line, allowing it to connect any two points together, regardless of whether they are on, above, or below the ground.
Examples of 3D line features include:
- underground transportation lines
- aircraft flight paths
- line-of-sight lines between buildings, and
- transportation networks inside skyscrapers
While it is also possible to model z-values using a numeric feature attribute, this option will display the feature with the same z-value for the entire line and may not support all the same analysis and interaction options supported with embedded z-values.
Any features that live exclusively on the elevation surface, such as streets, trails, and fence lines, should always be modeled as 2D line 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 lines, 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 polyline feature class
There are two main ways to create a 3D line feature class: you can either create a brand new line feature class or you can convert existing 2D line data into a new feature class that contains z-values.
|
To create a new 3D line feature class: |
Check the Coordinates include Z values check box when defining the feature class's geometry. |
|
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 lines, 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 polyline 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.