Filter

Source file: filter-group.htm

For a true representation of the tunnel's surface, unnatural objects such as pipes, cable trays, structural members, and mesh need to be filtered from the point cloud. The Services Filter group provides tools for identifying and excluding these unnatural features.

Services Filter

Filter out objects that are not part of the tunnel itself.

Underground Mesh

Hide mesh points from underground scans.

Services Filter

The Services Filter tool applies an attribute called Service to each point in the original point clouds, which will be set to 1 or 0 according to whether it is identified as belonging to a service or the tunnel surface, respectively. Points with Service = 1 will be hidden from view.

Note:  Because the hull surfaces tool includes services filtering, you only need to run the services filter to confirm your filtering options are correct first.

  • To filter unnatural objects, click on the Services Filter button in the Filter group of the Underground tab, then follow the steps below.

    1. Select the data to be filtered in the project explorer or the active view window.

    2. If required, select Handle objects independently.

      Note:  When this option is unchecked, the tool treats all selected point clouds as one, enabling better detection of the objects to be filtered. The results will usually be best with this option unchecked. If the filtering results are unsatisfactory, try again with this option selected.

    3. This tool requires defined centrelines. It can either calculate them, or use existing ones. Select either Automatically calculate centrelines or Provide centrelines. If selecting Provide centrelines, add the centrelines by selecting them in the project explorer.

      Note:  If you select Automatically calculate centrelines, centrelines are only calculated for the purposes of services filtering; no centreline objects are created.

      Tip

      If results are unsatisfactory, try either of the following:

      • Run the centrelines tool and ensure the centrelines are satisfactory. See Centrelines.
      • Draw custom-made centrelines with the Line tool. See Lines.

      After that, run this tool again using Provide centrelines.

    4. Select the Advanced tab to modify the services filter Settings. Do this if you're not satisfied with results from the default settings.

      Note:  Parameters are explained in mouse-over tool tips.

    5. Check Create geometry search objects if you need to analyse how the resulting services were determined.

      The services filter will create a container in the destination specified in the Advanced tab (scrapbook by default).

      planes These show the areas along the centreline that have been used to find the tunnel's shape. A single plane should capture all surrounding walls of one tunnel in a system. If the planes are too large they will detect data on nearby tunnels, if they are too small they will miss parts of the tunnel at that position. Adjust the size of these planes with Cross section separation in the Advanced tab.
      points The points represent the original points in the system which are considered to be on the plane. Cross section offset tolerance is the maximum distance a point can be from a plane to be considered on that plane's search.
      projected points A set of points representing the points found in points projected onto the plane from planes.
      hulls A convex hull wrapping the projected points.
      hull extrusions

      The convex hull, extended by Cross section separation to produce the total hull area at this cross section.
      hull extrusion points

      All points from the original data that are found to be on the "hull extrusion". This uses a search offset of Maximum distance from estimated hull. Points not found by a hull extrusion are the points which are considered to be services.

    6. Click OK or Apply.

Tip:  Bring the hidden points into view by clicking Show All in the Filter group of the Position and Filter tab. Use the Filter by Attributes tool to hide the filtered points again.

Underground Mesh

The Underground Mesh tool enables you to filter out wire reinforcement mesh from tunnel walls.

Filter out mesh points as follows:

  1. In the project explorer or view window, select the underground scan with the mesh to be filtered out.

  2. On the Underground tab, in the Filter group, click Underground Mesh.

  3. Select whether the walls have shotcrete or not.

  4. Click OK.

    Points on the walls identified as mesh will now be filtered with the mesh points coloured red.

  5. In the following panel adjust the Mesh confidence slider, or enter a value in the box. The view will dynamically display how much of the scan will be identified as mesh and filtered out.

  6. Select Keep mesh points to retain the mesh points in view and hide the rest. This will invert the point selection and colouring.

  7. Select the required Filter combination if the data have already been subject to a different filter. See Filter Combinations. 

  8. Click OK.

Note:  You can restore the filtered points to view by clicking Show All in the Filter group of the Position and Filter tab. However, to hide mesh points again, you will need to run the mesh filter again.