Identifying and modeling breakline features can significantly improve the accuracy of a TIN model and the associated contours. Breaklines are sharp changes in ground slope, e.g. edge of a road, creek bank, edge of ditch or a rock bluff.
Triangles should not be allowed to form across these features, since doing so would flatten the slope across the breakline. The Terrain module has a facility to handle these breaklines by not allowing triangle link lines to cross features with their breakline property on.
To Create a Breakline from an Existing Elevation Feature:
1. Select the elevation feature by left clicking on it with the selection cursor.
2. Select menu Edit Modify Selected Feature(s) - Properties, the Feature Properties dialog will appear.
3. The feature selected should have Elevation and Modeled already selected, if it doesn't see example Creating a New Breakline from a Draped Feature.
Often breakline features don't exist in the raw data. In this case, it may be necessary to create a breakline by drawing one with the mouse. This can be done as follows.
1. Select menu Edit - Calculate Terrain Model to create an initial TIN model (the TIN model is required to determine the elevations of the new feature).
2. Press the Draw New Feature on the toolbar to begin drawing the breakline.
3. Using the mouse, create points at existing triangle vertices (for more information on drawing a feature see Drawing and Editing a Feature). NOTE: the elevations of the new feature will be correct because the triangle vertices are at original elevations.
4. After drawing the feature, select menu Edit Modify Selected Feature(s) - Properties, the Feature Properties dialog will appear. Enable the Elevations and Modeled checkboxes.
5. You now have an elevation feature and can follow the procedure above (Creating a Breakline from an Existing Elevation Feature) to make this feature into a breakline.
