Purpose

The ShrinkWrap Tool in SPCAD generates a boundary polygon around the selected Point Group. Depending on the Concavity Index, the polygon can closely follow the outer shape of the points or form a smoother convex boundary.

Usage

• To use the ShrinkWrap Tool, open the Point Group Manager, select a Point Group, click the Create Features dropdown, and choose Create ShrinkWrap.
• A dialog appears with a slider labeled Concavity Index that controls how tightly the polygon follows the point distribution.

Concavity Index Settings

• Range: 0.05 to 1.0 
• Default Value: 0.5 

Visual Example

In the image shown: 

• A point group with ~9700 points is displayed. 
• The ShrinkWrap slider is set to 0.5. 
• The generated polygon captures the outer shape of the point distribution, maintaining some concavity. 

Similarly, the Concavity Index of 0.05 yields the following output.  

Output: 

• The tool creates a closed polyline in the drawing to represent the boundary.
• It places the polyline on the active layer.
• You can use this boundary for analysis, clipping, or visualization purposes.

When to Use ShrinkWrap

• Firstly, to define a clear working boundary around surveyed or imported points.
• Secondly, to prepare extents for TIN creation, raster clipping, or volume calculations.
• To visualize the actual spatial spread of point data more accurately than a convex hull.