# Working with 3D set operators

## What are they?

The 3D set operators are a collection of geoprocessing tools that allow for the geometric comparison of 3D features in ArcGIS. They can be used to investigate and determine the relationship between 3D features, such as checking if one feature is located inside another. They can also be used to create derivative features from input features, such as combining two cubes into a complex shape. There are six 3D set operation tools:

• Difference 3D: Subtracts one set of multipatches from another
• Inside 3D: Determines which features fall within a closed multipatch
• Intersect 3D: Computes the intersection of two closed multipatches
• Intersect 3D Line With Multipatch: Determines the points of intersection between a 3D line and multipatch
• Is Closed 3D: Determines whether a multipatch is closed and can be used in other set operations
• Union 3D: Combines closed multipatches with overlapping volumes into a single feature
Note:

Near 3D, which calculates the 3D distances between features, is often used in conjunction with 3D set operators.

 Difference 3D
 Intersect 3D
 Union 3D

## What are they used for?

These tools are commonly used to construct new features, provide quality control on existing features, and conduct spatial analysis. Below are some examples of how the 3D set operation tools might be used:

• Difference 3D: A city planner wants to estimate the impact for shadows cast by a proposed building. The planner generates a shadow volume for the new building using the Skyline tool suite, and then uses Difference 3D to subtract the shadows cast by existing buildings from the result. The end result is a volume representing the new shadows cast at that time of the day.
• Inside 3D: A facility manager is placing assets, as represented by points, in a 3D building model. Once all the assets have been placed, the room each asset falls within must be determined. The Inside 3D tool is used to generate a table that contains a row listing the ID of each asset and the ID of the room it falls within.
• Intersect 3D: A water quality specialist wants to see how much of an aquifer has been affected by a pollutant plume. The specialist uses Intersect 3D to generate a set of features representing the different geologic formations that are part of the aquifer, that also fall within the plume.
• Intersect 3D Line With Multipatch: A developer wants to determine whether a proposed building will negatively impact the views of existing buildings. Sight lines are generated from surrounding buildings to key points of interest. Those sight lines are intersected with the proposed building using the Intersect 3D Line With Multipatch tool, and any obstructions are identified.
• Union 3D: A city planner has received a collection of polygons with heights that represent buildings in the city. The planner needs to generate building shells from these polygons. The polygons are extruded and converted to multipatches, then combined using Union 3D into a single feature per building.

## Data requirements

Some 3D set operators require a closed multipatch to operate effectively. This is because the tools are calculating the relationship between a feature and the volume that a multipatch represents.

## Performance

Some 3D set operators are fairly process intensive and may take longer to execute. For example, Difference 3D and Intersect 3D require iterating through every feature in one input feature class, once for each feature in the second input feature class. Each iteration involves determining whether two features overlap, then computing their geometric intersection and writing a new unique feature. As a result, care should be taken when deciding what feature classes to use as inputs to these tools, regarding size and complexity of data.

Tip:

6/11/2012