While Revit doesn't natively have a "rolling sphere" function built-in for air terminal placement, here's a breakdown of the techniques, plugins, and strategies you can use to achieve a similar outcome

Understanding the Challenge:

The rolling sphere method (also known as the lightning protection system radius) is primarily used in lightning protection design. The challenge is to ensure the air terminals are positioned so that a sphere of a specific radius, rolled across the building surface, leaves no point on the roof exposed. Manually doing this on complex roofs with varying elevations is incredibly tedious.

Strategies and Tools to Emulate Rolling Sphere Placement in Revit


Visual Approximation and Careful Planning (Manual Method - Time Consuming)



Create Reference Planes

Establish horizontal reference planes at critical elevation changes.

Section Views

Create section views cutting through the roof at various points to visualize heights and potential exposed areas.

Circular Extrusions (Temporary Guides)

Create temporary circular extrusions with the radius of your rolling sphere. Position these at high points and along edges, visually determining where additional air terminals need to be placed. Remember to delete these extrusions after placement.

Manual Placement

Based on these visuals, manually place your air terminals.

Review and Iterate

Constantly review in 3D views, especially those showing roof slopes, and adjust placements as needed.

Pros

Free (uses built-in Revit tools).

Cons

Very time-consuming, prone to human error, not easily repeatable if design changes.2.

Dynamo Scripting (Intermediate to Advanced)



Dynamo is your most flexible option. You can write a Dynamo script that effectively simulates the rolling sphere method. Key Steps



Get Roof Geometry

Access the roof surface geometry using Dynamo nodes.

Create Points on Surface

Divide the roof surface into a dense grid of points.

Rolling Sphere Logic

For each grid point, imagine the center of a sphere with your specified radius is at that point. Determine if the entire sphere intersects the roof surface. If it doesn't, that point is potentially "exposed."

Exposed Point Detection

Identify which points on the roof surface are not intersected by a sphere centered at any of the surrounding grid points. These points are considered exposed.

Air Terminal Placement

Place air terminals at or near these "exposed" points. You'll likely need logic to cluster points and avoid placing air terminals too close together.

Visualization

Dynamo can show you the spheres and the points that are not covered, allowing you to validate your logic.

Customization

You can customize the script to: Handle different sphere radii. Consider existing air terminals in the placement algorithm (to avoid overlapping coverage). Optimize placement based on the shortest path to ground.

Pros

Highly accurate, repeatable, and adaptable.

Cons

Requires Dynamo knowledge (or hiring someone with that knowledge), more complex setup.3.

Add-ins/Plugins (Check the Market)



Revit App Store or Third-Party Developers

Search the Revit App Store (Autodesk App Store) or contact third-party Revit plugin developers. Specifically look for add-ins related to: Lightning protection design Coverage analysis Point cloud analysis (some might offer surface analysis tools useful for this)

Key Terms for Searching

"Lightning Protection," "Air Terminal Placement," "Coverage Analysis," "Surface Analysis"

Pros

Potentially easier to use than Dynamo (depending on the plugin), might offer features beyond simple rolling sphere simulation.

Cons

Cost (plugins can be expensive), might not perfectly match your specific needs, reliance on a third-party vendor.4.

Navisworks (Coordination and Clash Detection - Limited Use)

Navisworks can import your Revit model and perform clash detection. You could theoretically model the rolling sphere as a solid object. Then, use clash detection to identify areas where the sphere doesn't clash with the roof surface. Those areas are potential locations for air terminals.

Limitations

Requires manually creating and positioning the sphere. It's not an automated placement tool. More useful for verifying coverage than for generating placements.

Detailed Steps for Dynamo (Example - Adapt to Your Specific Needs)

This is a high-level outline. A fully functional Dynamo script is too extensive to provide here, but this guides you:1.

Get Roof Geometry

`Select Model Element` (or `Select Model Elements`) to select your roof. `Element.GetGeometry` (or `Element.GetGeometryEx` if you need more detailed geometry).2.

Create Points on Roof Surface

`Surface.PointAtParameter` or `Surface.UvIsoCurve` combined with `Curve.PointAtParameter` to create a grid of points on the roof surface. Adjust the U and V step values to control the density of the grid.3.

Define Rolling Sphere Radius

`Number Slider` or `Number` node to define the rolling sphere radius.4.

Rolling Sphere Logic (Core Algorithm)

This is the most complex part. For each point on the roof surface (the center of the "rolling sphere"): Create a sphere using `Sphere.ByCenterPointRadius`. Use `Geometry.Intersect` (or `Geometry.DoesIntersect`) to check if the sphere intersects the roof surface at other points. This determines if the sphere is "rolling" along the surface. If the sphere does not intersect the surface at enough other points (meaning it's "floating" in space), flag that point as potentially exposed.5.

Filter Exposed Points

Use a `FilterByBoolMask` to separate the potentially exposed points from the covered points.6.

Clustering and Optimization (Optional)

If you have too many exposed points, you might want to cluster them to avoid placing air terminals too close together. Use spatial analysis techniques (e.g., k-means clustering) in Dynamo to group points.7.

Air Terminal Placement

`FamilyInstance.ByPoint` to place your air terminal family at the filtered (and potentially clustered) points.

Important Considerations



Accuracy of Roof Model

The accuracy of your roof model is critical. Any discrepancies in the roof geometry will affect the accuracy of the air terminal placement.

Lightning Protection Standards

Consult local lightning protection standards and regulations (e.g., IEC 62305, NFPA 780) to determine the appropriate rolling sphere radius and air terminal spacing requirements. These standards often have specific rules about the maximum distance between air terminals and the shortest path to ground.

Electrical Grounding

Remember that air terminals need to be properly grounded. Consider the routing of grounding conductors when placing air terminals.

Maintenance Access

Ensure that air terminals are accessible for maintenance and inspection.

Aesthetics

Consider the aesthetic impact of air terminal placement. Sometimes, minor adjustments can improve the overall appearance without significantly compromising lightning protection.

Recommendations


Start with a simple roof

Practice with Dynamo on a simple roof model before tackling complex roofs.2.

Break down the problem

Decompose the rolling sphere method into smaller, manageable Dynamo tasks.3.

Test thoroughly

Validate your Dynamo script by visually inspecting the placement results and comparing them to manual calculations.4.

Consider a plugin (if available)

If you find a suitable Revit plugin that automates the process, it might save you significant time and effort compared to Dynamo scripting.5.

Iterative Design: Remember this is an iterative process. You might need to adjust your script or workflow as you gain more experience.Good luck! Let me know if you have any more specific questions as you work on this. Flag for review