Written by: Mackenzie Mills, Application Specialist
One of the renowned strengths of Global Mapper® is its terrain processing functionality, and with each successive release, there are significant enhancements to the terrain creation, editing, analysis, and exporting tools, In the latest version of the Lidar Module®, a new Terrain Painting tool, allows for the manual manipulation of terrain by using the cursor like a brush to paint and edit the elevation surface in various ways.
The Terrain Painting tool can be found in the Analysis toolbar or Analysis menu. When enabled, a Terrain Painting Options dialog box appears in which a brush type and operation to use are selected when editing terrain data.
The point and line brush types include the option to set the brush size in grid cell size or pixel resolution increments, derived from the layer being edited. This value can be determined in the metadata for the terrain layer. For example, if the cell size for a layer is 5-meters, a 10-grid cell brush would be 50 meters in diameter. For a point brush type, the terrain within the extent of the brush will be modified based on the selected operation.
When using the line and area brush types, the terrain editing process is similar to that of the digitizer tool. Left-clicking with the mouse places vertices, and right-clicking sets the final line vertex or closes the area feature. With the line brush type, the brush’s center corresponds with the drawn line, and the brush size determines how far from the line the terrain will be edited. With the area brush type, the entire area inside the drawn bounds is edited by the selected operation.
With some operations, feathering is used to blend edited values into the surrounding terrain. For the Raise Terrain, Lower Terrain, and Set Terrain Height operations, a feathering distance in grid cells can be set to provide a smooth transition between the original elevations and the altered elevation areas.
Fill Gaps use this tool to fill holes or null areas in the terrain with the inverse distance weighting (IDW) method using values from surrounding pixels. This operation is useful for filling holes in terrain data derived from a fragmented or incomplete point cloud.
Below, a digital terrain model (DTM) has been generated from a classified point cloud, and gaps have been left where building features were present. Using the Fill Gaps operation, holes in the data can be closed to create a solid DTM layer.
Using the point brush type with a specified brush size, smaller gaps in the data can be filled with using same method.
Smooth alters the elevation values for the pixels within the area, based on the specified box size. By default, the box size is set to 5×5 grid cells, so each cell within the brush area is altered based on the average elevation within the 5×5 neighborhood surrounding that specific cell.
Raise Terrain and Lower Terrain either raises or lowers selected terrain cells’ elevation by a specified value. This is used to offset the elevation values for specific sections of the existing terrain.
Below, a path along a canal is raised half a meter using the line brush and the Raise Terrain operation. This altered terrain will impact further analysis of the terrain, like with the watershed and flooding simulation tools.
When viewed in 3D, the feathering between the flatter raised path and the nearby terrain is clearly visible. The feathering creates a more realistic bank and prevents an abrupt dropoff from the altered values to the nearby unedited values.
Set Terrain Height applies a specific elevation within the brush extent. Unlike the above raise and lower terrain options, this operation \overwrites the existing elevation using the defined height value. This operation can be used to flatten an area of terrain and fill in gaps in the data, as shown in the below example. The image on the right shows a pond area with some data missing. The surface of the pond is rough due to noise in the original point cloud. Using the area brush type and the Set Terrain Height operation with a value of 26 meters, the areas of no data are filled, and the pond area is flattened to the appropriate height.
Set to “No Data” creates gaps in the terrain by removing data from the designated area. This can be a useful first step to clear anomalies in the data before using another terrain painting operation to close the data gaps based on the surrounding elevation values.
To remove the bump in the terrain created by a truck, the data must first be removed for the area.
After removing the data for the truck feature, the Fill Data operation is used to fill in the area of no data. This process flattens the lump in the terrain caused by the truck’s inclusion in the original data.
Revert to Original Heights undoes any changes made to the terrain and will revert the pixel elevations to their original values.
The Lidar Module’s Terrain Painting tool provides a direct and interactive way to edit terrain data With multiple operations and methods to apply edits, there are a wide variety of uses for this tool. All terrain edits are saved in the Global Mapper workspace and are retained when exporting layers to a file. This innovative tool provides the means to sculpt the terrain reflecting artificial modifications and to improve the quality of terrain layers by removing unwanted features or anomalies before continuing with complex analysis procedures.
If you’re not familiar with Global Mapper and the Lidar Module, request a two-week free trial today. If you would like to speak with a representative about how the software can address your unique geospatial challenges, request a demo!