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

TIN without a polygon added

Clip polygon added to the TIN

Clip polygon

Erase polygon added to the TIN

Erase polygon

Replace polygon added to the TIN

Replace polygon

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. Under TIN Layer, click the Data tab.
  3. Click the TIN Editor button TIN Editor.
  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 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 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

    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.
  7. 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 sourceDescription

    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.

    TIN
    A TIN with no replace polygon is shown.
    Replace polygon
    A TIN with a replace polygon without a replace offset is shown.
    Replace offset applied to the polygon
    A TIN with a replace polygon with a Replace Offset value is shown.

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

    The first vertex is digitized on the surface.

  9. Continue to add each vertex to the polygon by a clicking the locations for each.
  10. Double-click to finish the new polygon.
  11. Click the Save button Save Edits to save the edits to the TIN currently being edited. Once the TIN is saved, all edits are permanent and cannot be undone. Click the Discard button Discard Edits to discard all unsaved edits. To create a copy of the TIN with the current edits applied, click the Save As New TIN button Save As.
  12. Click the Close TIN Editor button Close to close the TIN Editor when edits are completed.

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