Add a polygon to a TIN

To add a polygon to an editable TIN, use the Add Polygon tool from the TIN Editor.

Polygons are shapes used either to define the data area of a TIN or to flatten an area in a TIN. You can add a clip, erase, or replace polygon.

Clip polygons define a boundary for the TIN surface. Input data that falls outside the clip polygon is excluded from the interpolation and analysis operations. Erase polygons are also used to define a boundary for interpolation. Input data that falls within the erase polygon is excluded from the interpolation and analysis operations. Replace polygons set the boundary and all interior heights to the same value, making those areas horizontal or flat. A replace polygon could be used to model a lake or an area on a slope graded to a level surface.

Original TIN without any polygons added
Clip polygon added to the TIN
Erase polygon added to the TIN
Replace polygon added to the TIN

Add a polygon

To interactively add a polygon to a TIN, follow the steps below:

1. In the Contents pane, select the TIN layer you want to edit.
2. Click the Data tab from the TIN Layer tab set.
3. Click the TIN Editor button .
4. Click the Add Polygon button.
5. Click the type of polygon you want to add from the drop-down menu.

   The choices are as follows:

   Add Clip Polygon	Clip polygons define a data area boundary for the TIN surface. Input data that falls outside the clip polygon is excluded from the interpolation and analysis operations.
   Add Erase Polygon	Erase polygons are used to cut holes in a TIN. Input data that falls within the erase polygon is excluded from the interpolation and analysis operations.
   Add Replace Polygon	Replace polygons set the boundary and all interior heights to the same value. A replace polygon can be used to model a lake or an area on a slope graded to a level surface.

   The dialog box that allows you to set properties for the polygon appears.

6. Set the properties for the polygon to be created on the TIN surface.

For Line Type, choose either Hard or Soft. Hard and soft qualifiers for polygon feature types are used to indicate whether a distinct break in slope occurs on the surface at their location. A hard line is a distinct break in slope, while a soft line is represented on the surface as a more gradual change in slope. This difference only applies when natural neighbor interpolation is used on a TIN. Hard and soft lines have the same effect with linear interpolation.

The Height parameter specifies the height source to be used to generate the polygon on the TIN surface. Choose from As specified, From surface, Max Z from surface, or Min Z from surface. From surface is not an option when you add a replace polygon.

Height source	Description
As specified	The elevation of the digitized polygon is added to the surface at a constant specified elevation value set in the height field.
From surface	The elevation of the digitized polygon boundary is interpolated from the selected locations on the surface.
Max Z from surface	The elevation of the digitized polygon is assigned the maximum height that is encountered though interpolation along the polygon boundary.
Min Z from surface	The elevation of the digitized polygon is assigned the minimum height that is encountered though interpolation along the polygon boundary.

Optionally, set a Replace Offset value when adding a replace polygon.

When a Replace Offset value is used to add a polygon, the polygon you digitize will be added as a breakline, obtaining its heights from the surface. This polygon is used to hold the terrain along that boundary in place. The polygon is then buffered inward by the replace offset and inserted using the replace height. Therefore, two polygons are created. The outer polygon always lies on the surface, while the inner polygon has a specified height value used for flattening.



A TIN with no replace polygon is shown.



A TIN with a replace polygon without a replace offset is shown.



A TIN with a replace polygon with a Replace Offset value is shown.

7. Select a point on the TIN surface where the polygon will start.

   The first vertex is digitized on the surface.

8. Continue to add each vertex to the polygon by clicking the locations for each.
9. Double-click to finish the new polygon.
10. Click the Save button to save the edits to the TIN currently being edited or click the Discard button to discard all unsaved edits. To create a copy of the TIN with the current edits applied, click the Save As New TIN button .

    Once the TIN is saved, all edits are permanent and cannot be undone.

11. Click the Close TIN Editor button to close the TIN Editor when edits are completed.