Topography

Source file: filter-by-topography.htm

The Topography filter (Ctrl+T) removes unwanted features, such as vegetation, machines and infrastructure, from scans and retain only the relevant topographic surface.

The topography filter divides the scan data into a horizontal grid with a user-defined cell size. Only the single lowest or highest point in each cell is retained to remove unwanted features and reduce the data to a more even point distribution.

• To filter by topography, follow these steps:
  

1. Select the scans to be filtered.
   

2. On the Position and Filter tab, in the Filter group, click Topography.

   

3. Specify a Search cell size and whether to keep Lower points or Upper points.

   Note

   • The cell size should typically be between 0.5 and 2 m. If the cell size is too large, edges will be excessively rounded.

   • Only use Upper points in an underground situation to retain the roof.

4. To remove vegetation points, select Limit maximum slope and set an appropriate angle. This will remove any points inside an inverted cone projected upwards from any point.

   

   Tip:  The default maximum slope is 35°. Try different angles to find the optimum filtering.

5. Select the required Filter combination (see Filter Combinations). 

6. Select or clear Apply filter to selection as a whole as required:

   • If selected, the filter treats all selected objects as a single object.

   • If cleared, each selected object is filtered independently.

7. Click OK or Apply.

A scan to be filtered (truck to be removed).

The result of topographic filtering. Any unwanted points remaining must be removed manually.

Tip:  You can redisplay filtered points by clicking Show All. See Show All.