ADDING BREAKLINES TO YOUR DRAWING

•You can use breaklines to define retaining walls, curbs, tops of ridges, centerline of channels and streams.

•Breaklines force surface triangulation along the breakline and prevent triangulation across the breakline.

•Breaklines are typically critical to creating an accurate surface model, because it is the interpolation of the data, not just the data itself, that determines the shape of the model.

•The breaklines are automatically drawn on the SRF-FLT layer by default, but you can change this layer.

You can define proximity breaklines from polylines that are not drawn exactly from sampled point to sampled point, but are in the proximity of the points. Each vertex point in the polyline can be in the proximity of a sampled point. When the surface model is calculated, each vertex point of that breakline snaps to the nearest sampled point. Because you don't have to draw the polylines from exact points, the proximity breakline command makes it quicker and easier to define a breakline. This command adds a breakline into the database based on polyline vertex northing and easting coordinates. The elevational value at each vertex point of the breakline is 0. When you build the surface model, the proximity breakline points snap to match the nearest sampled points. After the model is created, you can import the proximity breakline to see what points were used in the breakline definition.

Why add Breaklines?

define channels Define top of bank Define toe of slope Define retaining walls or curbs as breaklines to be

used as surface data.

You can define proximity breaklines by selecting locations close to sampled points (any breakline point, contour point, or COGO point used to create a TIN). A breakline is added into the database based on the northings and eastings of the selected locations.

When you build the surface model, the proximity breakline points snap to match the nearest sampled points. After the model is created, you can import the proximity breakline to see what points were used in the breakline definition.

  You can use 2D or 3D polylines as breaklines to create a surface. The X, Y, and Z coordinates of each vertex on the polyline that you select are written to the breakline file.

WARNING!  If you select a 2D polyline with a zero elevation, then it is saved in the breakline file with that elevation. Use proximity breaklines if you want the program to calculate the elevations.

Areas like these can be better defined with the use of breaklines.

CREATING SIMPLE BREAKLINES

To better define a channel or place on a survey where you do not intend to have the contours cross, you can install a breakline.

With the O-snaps on, draw a polyline from Node to Node on your drawing. It is important to strike the node precisely, as the polyline assumes the elevation of that node in that location.

In Terrain, select Terrain Model Explorer.

Click on the plus sign to open your existing ground surface. Here it is called Surface 1.

Right Click on Breakline and select Proximity by Polylines.

Notice the Command Line: Enter a description for the Breakline.

Select the polyline you just created.

Select Yes to Delete existing objects. AutoCad will draw the breakline where the polyline was.

Notice the breakline numbers are now on the menu manager. It is one line with seven vertices. Close dialogue box.

Make sure the Use breakline data box is checked. Select OK

Right click on Surface 1 and select Build.

From the Terrain Menu, select create contours.

At the command line Select Yes to Erase old contours.

New contours should represent the surface.