Bentley Descartes CONNECT Edition

Ground Extraction Tool

The Ground Extraction tool extracts terrain and automatically classifies ground points in reality models (reality meshes and point clouds).

Access the tool:

  • Realty Modeling workflow Extract tab > Reality Models: Ground Extraction.
  • Open Reality Mesh attachments dialog then select Tools.
  • Open Point Cloud Manager then select Tools.

The tool creates or imports known ground points, named "seed points". Those seed points are used to create a coarse Triangular Irregular Network (TIN) that is densified according to the tool's parameters. Outputs are produced from the densified TIN.

Note: Note: When working with a reality mesh, the model’s resolution is determined by the “Export Resolution” setting. To change this setting:
  1. Select a reality mesh attachment.
  2. Open the "Properties" dialog.
  3. Navigate to the "Reality Mesh" section.

Setting

Description

Seed Mode

Choose provenance of seed points.
  • Automatic: The “Largest Infrastructure Size” parameter is used to compute a grid over the reality model. The lowest points in each tiles are used as seed points.
  • Points: Use vertexes of elements found in the selected DGN Level as seed points.
KEY-IN: REALITYMODEL GROUNDEXTRACTION SEEDMODE [AUTOMATIC | POINTS]
KEY-IN: REALITYMODEL GROUNDEXTRACTION LEVEL
KEY-IN: POINTCLOUDADV GROUNDEXTRACTION SEEDMODE [AUTOMATIC | POINTS]
KEY-IN: POINTCLOUDADV GROUNDEXTRACTION LEVEL

Largest Infrastructure Size

Smallest side of largest man-made object in reality model. When a grid is computed using this value, each of the grid’s tiles must contain at least one ground point.
KEY-IN: REALITYMODEL GROUNDEXTRACTION MAXTRIANGLEEDGE
KEY-IN: POINTCLOUDADV GROUNDEXTRACTION MAXTRIANGLEEDGE

Terrain Variation

Use a smaller value when reality model’s terrain is flat and a higher value when hilly. Default value is 5.
KEY-IN: REALITYMODEL GROUNDEXTRACTION TERRAINVARIATION
KEY-IN: POINTCLOUDADV GROUNDEXTRACTION TERRAINVARIATION

Output

At least one of the following outputs must be selected:
  • Seeds
  • Terrain
  • Scalable Mesh
  • Classified Point Cloud

Seeds

Saves “automatic” seed points to the selected DGN Level. Saved seed points can be edited and reused by choosing the “Points” Seed Mode.
KEY-IN: REALITYMODEL GROUNDEXTRACTION SEEDS [ON | OFF]
KEY-IN: REALITYMODEL GROUNDEXTRACTION LEVEL
KEY-IN: POINTCLOUDADV GROUNDEXTRACTION SEEDS [ON | OFF]
KEY-IN: POINTCLOUDADV GROUNDEXTRACTION LEVEL

Terrain

Saves the densified TIN to a Geopak Tin file (*.tin) and automatically generate, and attaches, a Scalable Terrain Model.
KEY-IN: REALITYMODEL GROUNDEXTRACTION TERRAIN [ON | OFF]
KEY-IN: POINTCLOUDADV GROUNDEXTRACTION TERRAIN [ON | OFF]

Classified Point Cloud

Automatically classifies the ground points that are within a threshold of the densified TIN. When the reality model is a reality mesh, a point cloud is extracted according to the reality mesh’s “Export Resolution” and classified.

Classification Tolerance:

  • Automatic: Use last densification parameter to compute classification threshold.
  • Manual: Specify classification threshold.
KEY-IN: REALITYMODEL GROUNDEXTRACTION CLASSIFY [ON | OFF]
KEY-IN: REALITYMODEL GROUNDEXTRACTION CLASSIFYMETHOD [AUTO | MANUAL]
KEY-IN: REALITYMODEL GROUNDEXTRACTION CLASSIFYTHRESHOLD
KEY-IN: POINTCLOUDADV GROUNDEXTRACTION CLASSIFY [ON | OFF]
KEY-IN: POINTCLOUDADV GROUNDEXTRACTION CLASSIFYMETHOD [AUTO | MANUAL]
KEY-IN: POINTCLOUDADV GROUNDEXTRACTION CLASSIFYTHRESHOLD

Max. Triangle Edge

Stop adding ground point inside triangle for which edge length value is smaller than this threshold.
KEY-IN: REALITYMODEL GROUNDEXTRACTION MAXTRIANGLEEDGE
KEY-IN: POINTCLOUDADV GROUNDEXTRACTION MAXTRIANGLEEDGE

Advanced Output Settings

Turn advanced settings ON to automatically create output files.
KEY-IN: REALITYMODEL GROUNDEXTRACTION ADVANCESETTINGS [ON | OFF]
KEY-IN: POINTCLOUDADV GROUNDEXTRACTION ADVANCESETTINGS [ON | OFF]

Filename

Filename to be used when output files are created automatically.
KEY-IN: REALITYMODEL GROUNDEXTRACTION FILENAME
KEY-IN: POINTCLOUDADV GROUNDEXTRACTION FILENAME

Directory

Directory to be used when output files are created automatically.
KEY-IN: REALITYMODEL GROUNDEXTRACTION DIRECTORY
KEY-IN: POINTCLOUDADV GROUNDEXTRACTION DIRECTORY

Existing File

Choose what to do when automatically created output files already exist.

  • Overwrite
  • Increment Name
KEY-IN: REALITYMODEL GROUNDEXTRACTION EXISTINGFILE [OVERWRITE | INCREMENT]
KEY-IN: POINTCLOUDADV GROUNDEXTRACTION EXISTINGFILE [OVERWRITE | INCREMENT]
KEY-IN: REALITYMODEL GROUNDEXTRACTION
KEY-IN: POINTCLOUDADV GROUNDEXTRACTION
Parent topic: Reality Model Tools