To generate points for a surface

Using a surface model of the natural ground surface to compare to a measured weld is a great way to compute the cover depth. If you have LIDAR data then that data can be used as the surface, but if you have to complete a topo survey to define the surface then this can be a lot of work. The pipeline route is usually surveyed to determine elevations along the route and identify changes in grade, but the survey is often in a single line along the proposed alignment with little width to the survey. To create a surface model, you need elevation data that has some width. Given that the pipeline will be positioned fairly close to the alignment, it is safe to assume that in many situations, projecting the topo data for the alignment out to the width of the corridor along the alignment will be accurate enough to create a surface from the projected points, as any cover calculations will be for positions close to the alignment.

The Generate points for a surface function allows you to select topo points along the alignment and then project them to the left and right of the alignment, creating new points at the same elevation as those that were projected. From the map, the original points and the projected points can then be used to create a surface.

  1. Tap and select Cogo / Generate points for a surface.

    The fields in the Generate points for a surface screen show the width values selected in the Pipelines options screen. Any changes you make to the fields in this screen are also made in the Pipelines options screen.

  2. If required, select a pipe alignment file in the Pipe alignment field and edit the values in the Corridor width fields.
  3. To add the points surveyed at ground level above the alignment:
    1. Tap Add.
    2. In the Start point and End point fields, enter the point name, or use the arrow to select the point from a list of points in the job, by search, or from a list of points currently selected in the map.
    3. Tap Add.
  4. In the Generate points for a surface screen, select the name to use for the first new point created in the surface.
  5. If required, enter the code to use for the surface points in the Code field. If the code you want to use is not listed in the feature library screen, enter the code in the text field at the top of the feature library screen and then tap Enter.

  6. Tap Create.

    A message confirms the number of new points created.

  7. Tap OK.

    The Generate points for a surface screen closes and you are returned to the map.

  1. In the map, select the points to use to create the surface:
    • Directly in the map.
    • Tap and hold in the map and tap the Select option to select points using a different method. For more information, refer to the Trimble Access Help.
  2. From the tap and hold menu, select Create surface.

  3. Enter a name for the surface.

    A surface is generated from the current point selection and stored as a Trimble Terrain Model file (surface name.ttm) in the current project folder.

    The newly-created surface appears in the map.

  4. To use the surface you have just created for depth of cover calculations, see To configure Pipeline options.