Decimating Terrain Meshes

You can decimate a mesh, i.e. reduce its triangle count to save computation time (many large meshes can be represented accurately with fewer triangles). Decimating a mesh also reduces the memory requirements for the model. Decimate is performed on the entire region.

Before you begin: This command is available in 3D Printing Preparation, not in 3D Printing.
  1. From the Prepare section of the action bar, click Decimate.
  2. Select a mesh exempt of non-manifold problems, even on non-active areas.
  3. Select the type of decimation to apply.
    • Chordal Deviation to preserve the shape of the model, even in areas with a high curvature.
    • Edge Length to remove triangles with tiny edges and obtain a more uniform mesh. However this may result in a loss of accuracy in areas with a high curvature.
  4. Enter the parameter values for the selected type of decimation.
    • For a decimation by Chordal Deviation, select the Maximum check box and enter a value. It is the chordal deviation that should not be exceeded during decimation. Decimation stops when the chordal deviation limit has been reached. Example: Decimation with a Chordal Deviation at 70%.
    • For a decimation by Edge Length, select the Minimum check box and enter a value. The minimum edge length is then represented by a sphere. Decimate stops when further decimation could collapse edges of length greater than the value entered. Example: Decimation by Edge Length set at 70%.
    • For both types of decimation, select the Target Percentage check box to obtain a given final number or percentage of triangles. Either enter the percentage value or the Target Triangle Count. Those boxes are linked to each other and updated simultaneously.
    • Current Triangle Count indicates the current number of triangles, either of the original model when you start the action, or of the result model when you have clicked Apply.
  5. To control the decimation of free edges, when a rectangular shape sees its corners cut off after decimation, select the Free Edge Tolerance check box. This check box activates the maximum allowable deviation that can occur for vertices on the boundary.
    The distance between the resulting decimated boundary and the original boundary remains under the set tolerance.
  6. Select the Analysis check box before clicking Apply to see the maximum distance and the mean distance between the original mesh and the result mesh at the end of the computation.

    The chordal deviation that can be used as a stopping criterion is an approximation of the chordal deviation between the original mesh before decimation and the decimated mesh

    At the end of the decimation, the maximum, and the mean deviation are reported. Unlike the value entered under Maximum, these are the true deviations between the original mesh and the result mesh.
    Warning:
    • An analysis may be time consuming, especially for large models.
      Recommendation: Turn it off when you do not need it.
    • The meshes can be decimated in several steps (click Apply= one step). The deviations displayed are those between the original model and the last result (not those between the previous and the current results).
    • Any selection change resets the original model for the analysis.
    • Undo is not taken into account by the analysis.