Overview 

Erode Hole removes (excavates) a portion of an existing TIN Surface using a closed polygon boundary. First, the tool identifies the defined boundary and rebuilds only the affected portion of the triangulation. As a result, a new TIN Surface is created as output, while the original surface remains unchanged.

Therefore, this tool is especially useful for modeling scenarios such as:

• Excavation pits or borrow areas, where material is intentionally removed
• Ponds and basins, requiring clean, well-defined depressions
• Removals for structures or voids, such as foundations or underground spaces
• Cut-outs, where the surface should no longer exist and must transition cleanly to the surrounding terrain

Requirements 

Before running the tool, ensure: 

1. A TIN Surface is selected in the TIN Surface Manager 
   • The selected surface will be treated as the input surface. 
2. You have a valid boundary polygon: 
   • A Closed Polyline (recommended) 
   • Or you can choose the option to Draw Polygon when prompted 

Workflow Summary 

1. Select a TIN Surface in TIN Surface Manager 
2. Start Erode Hole 
3. Choose boundary method: 
   • Select Closed Polyline 
   • Draw Polygon 
4. Tool processes the surface and boundary 
5. A new TIN Surface is created with the hole eroded 

Erode Hole TIN Surface: Step-by-Step Usage

Step 1 — Select Input Surface 

1. Open TIN Surface Manager 
2. Click to highlight/select the TIN surface you want to modify  (This is the surface that will be eroded.) 

If no surface is selected, the tool cannot proceed. 

Step 2 — Start the Erode Hole Command 

Run the command from: 

• Ribbon/menu (if provided) 
• Command line (tool command name) 
• Toolbar button (if configured) 

You will be prompted to define the excavation boundary. 

Step 3 — Define the Hole Boundary 

You will be given two options: 

Option A — Select Closed Polyline 

• Select an existing closed polyline in the drawing. 
• The polyline should represent the area to be removed. 

Best choice if you already have a design polygon or footprint. 

Option B — Draw Polygon 

• If you choose Draw Polygon, you will be asked to pick points to create a polygon. 
• Finish the shape to close it (based on the tool prompt workflow). 

Best for quick, manual excavation shapes. 

Step 4 — Tool Creates the New Surface 

After you define the boundary, the tool performs the following steps:

• First, it identifies the triangles impacted by the boundary.
• Next, it rebuilds the triangulation only within the affected “patch” region.
• Then, it removes the triangles inside the excavation boundary.
• As a result, the tool creates a new TIN Surface.
• Finally, it stores the surface as a separate dataset, ensuring the original surface remains intact.

Output from Erode Hole TIN Surface

What you get

• As a result, you get a new TIN Surface that matches the original surface everywhere except within the eroded region.
• Within this region, no triangles remain, creating a true “hole” or void in the surface.

What is not changed

• Meanwhile, your original TIN Surface remains completely untouched.
• Additionally, all existing triangles outside the affected zone are preserved, ensuring fast performance and stable results.

Usability Notes 

Boundary placement rules 

• The boundary may be fully inside the surface, or partially outside the surface. 
• If the boundary crosses the surface edge, the tool automatically clips the excavation to the valid surface area. 

The boundary must be a single closed loop 

• Open polylines are rejected 
• Polylines with self-intersections can cause failure or unexpected results 

Tips for Best Results 

1) Use clean, simple boundaries 

• Avoid extremely dense polylines with thousands of vertices. 
• Avoid overlapping segments or tiny zig-zag vertices. 
• If the boundary was generated from complex clipping, consider simplifying it. 

2) Avoid self-intersections 

Boundaries that cross themselves can create ambiguous regions and may fail. 

Tip: If unsure, run a quick check by converting it to a Region in CAD manually. 

3) Stay away from ultra-small slivers 

If your boundary creates a very thin slice along the edge of the TIN, triangulation may become unstable. 

Tip: Slightly adjust the boundary inward/outward to remove near-zero-width “sliver” areas. 

4) Ensure your TIN boundary is valid 

If the input surface has broken edges, missing boundary metadata, or non-manifold triangulation, excavation might behave unpredictably. 

Performance Tips 

Large surfaces 

On large TINs, performance depends mostly on: 

• number of triangles intersected by the boundary 
• complexity of the boundary 

Because the tool re-triangulates only the affected band, it remains fast even for very large surfaces when the excavation area is small. 

Progress / Cancel 

A progress window is shown during processing. 

• You can cancel the operation at any time. 
• On cancel, the tool returns without creating a new surface. 

Common Issues & Fixes 

“Nothing happens” / No new surface created 

Possible causes: 

• The boundary does not intersect the TIN at all 
• The boundary is outside the surface 
• The affected triangle band is empty 

Fix: 

• Move the boundary so it overlaps the surface 
• Confirm you selected the correct TIN in the manager 

Errors during triangulation 

Most common causes include:

• First, the boundary has self-intersections.
• Additionally, the boundary overlaps itself or contains duplicate points.
• In some cases, the boundary creates extremely tiny slivers.

To fix these issues:

• Start by simplifying the boundary polyline.
• Next, remove any duplicate vertices.
• Finally, avoid creating razor-thin shapes, especially near the surface edge.

Recommended Practices 

Naming convention 

When creating the new TIN surface, use a name like: 

• OriginalName_ERODE_01 
• Surface_PondHole 
• Existing_ExcavationCut 

This helps track edits and allows multiple excavation variants. 

Preserve originals 

Because this tool generates a new surface, it is ideal for: 

• comparing design options 
• performing QA checks 
• preserving existing conditions