Tutorial: Editing Surface Data

This tutorial demonstrates some common surface editing tasks, including edge swapping, TIN line deletion, and surface smoothing. You will also hide part of the surface using a hide boundary.

For more information, see the AutoCAD Civil 3D Help topic Surface Editing Operations.

Edge Swapping

Edge swapping is used to change the direction of two triangle faces in the surface, to create a more accurate surface model.

For example, edges can be swapped to match the triangle edges to ridges or swales.

Click to view the effects of edge swapping.

Deleting TIN Lines

Deleting TIN lines may be required, for example, if the surface has TIN triangles on the perimeter that are long and narrow.

In this case, the triangles might not be accurate for the surface, and should be deleted.

Surface TIN or Grid lines can also be deleted within a pond, for example, to create a void area. By removing these lines, you can prevent contours from being drawn through the void areas.

When an edge is removed, either an interior border that follows the adjacent lines is created, or the exterior border is modified to follow the new lines.

Hide Boundaries

Hide boundaries mask areas of the surface so triangulation, and therefore contours, are not visible in the area. Use hide boundaries to create holes in a surface, for example, to mark a building footprint.

Click to view the effects of a hide surface boundary.

Note

When you use a hide boundary, the surface is not deleted. The full surface remains intact. If there are surface TIN lines that you want to permanently remove from the surface, use the Delete Line command.

Surface Smoothing

Surface smoothing is an operation that adds points at system-determined elevations using Natural Neighbor Interpolation(NNI) or Kriging methods. The result is smoothed contours, with no overlap.

You perform smoothing as an edit operation on a surface. You can specify smoothing properties and then turn them on or off. When the smoothing is turned off, the surface reverts back to its original state. However, the smoothing operation remains in the surface operation list, and it can be turned on again.

NNI is a method used to estimate the elevation (Z) of an arbitrary point (P) from a set of points with known elevations.

This method uses information in the triangulation of the known points to compute a weighted average of the elevations of the natural neighbors of a point.

Click to view the nearest neighbors of an arbitrary point (p).

To use NNI, specify only the output locations of the interpolated points. The elevations of the interpolated points are always based on the weighted average of the elevations of the existing neighboring points. NNI interpolates only within the surface.

Topics in this section

 Exercise 1: Swapping TIN Edges

In this exercise, you will swap several TIN edges in a surface.

 Exercise 2: Deleting TIN Lines

In this exercise, you will delete TIN lines from a surface.

 Exercise 3: Adding a Hide Boundary

In this exercise, you will create a hide boundary on the surface, which will mask unwanted triangulation.

 Exercise 4: Smoothing a Surface

In this exercise, you will smooth a surface using the Natural Neighbor Interpolation (NNI) method.

4.4.1 Exercise 1: Swapping TIN Edges

In this exercise, you will swap several TIN edges in a surface.

For more information, see the AutoCAD Civil 3D Help topic Swapping Edges. Swap TIN edges

1. Open Surface-4A.dwg, which is located in the tutorials drawings folder .

In this drawing, the surface is displayed as TIN lines overlaid on an externally referenced landbase image.

2. Zoom in to the lower edge of the surface.

Click to view the area to zoom to

3. In Toolspace, on the Prospector tab, expand the surface Definition collection. Right-click Edits.

4. Click Swap Edge.

On the command line, you are prompted to select an edge (line) to swap.

5. Click a TIN edge to swap it.

Click to view the recommended edges to swap.

The edge is swapped if the following criteria are met:

 Two visible triangles are separated by the edge.

 The quadrilateral formed by the two triangles (which are separated by the edge) is convex.

6. Optionally, continue to click other TIN edges to swap them.

7. Press Enter to end the command.

The edits are added as Swap Edge operations to the Edits list view on the Prospector tab.

Note

The Description column in the list view provides the coordinates of the pick point along the edge that was swapped.

To continue this tutorial, go to Exercise 2: Deleting TIN Lines.

4.4.2 Exercise 2: Deleting TIN Lines

In this exercise, you will delete TIN lines from a surface.

The TIN lines fall within a pond. By removing these lines, you can prevent contours from being drawn through the pond area.

For more information, see the AutoCAD Civil 3D Help topic Deleting TIN or Grid Lines. This exercise continues from Exercise1: Swapping TIN Edges.

Delete TIN lines

1. Open Surface-4B.dwg, which is located in the tutorials drawings folder .

In this drawing, the surface is displayed as TIN lines overlaid on an externally referenced landbase image.

2. Zoom in to the rounded pond area in the upper left of the surface.

Click to view the lines that cross the pond area.

3. In Toolspace, on the Prospector tab, expand the surface Definition collection, and right-click the Edits item.

4. Click Delete Line.

On the command line, you are prompted to select an edge (line) to remove.

5. Click an edge that crosses the surface of the pond. Press Enter.

The edge is removed and an interior border is created, following the adjacent TIN lines.

6. Repeat the Delete Line command and remove all TIN lines that cross the pond surface.

Tip

Enter C on the command line to use crossing selection during the delete line command.

Click to view the revised triangulation and see how the interior border should appear.

The edits are added as Delete Line operations to the Edits list view in Prospector.

Note

The Description column in the list view provides the coordinates of the vertices for the edge that was deleted.

To continue this tutorial, go to Exercise 3: Adding a Hide Boundary.

4.4.3 Exercise 3: Adding a Hide Boundary

In this exercise, you will create a hide boundary on the surface, which will mask unwanted triangulation.

A boundary can be created from any polygon or polyline, but in this exercise you will use an existing breakline.

For more information, see the AutoCAD Civil 3D Help topic Boundaries. This exercise continues from Exercise 2: Deleting TIN Lines.

Add a hide boundary

1. Open Surface-4C.dwg, which is located in the tutorials drawings folder . Note

This drawing is similar to Surface-3.dwg with the addition of the C-TOPO-BRKL layer, which displays breaklines.