WEMReducePolygons

MLModule

genre	WEMProcessing
status	stable
author	Bart De Dobbelaer
package	MeVisLab/Standard
dll	MLWEMModules
definition	MLWEMModules.def
see also	WEMSubdivide
keywords	WEM, collapse, reduce, reduction, simplification, quadric, error, metric

Purpose

The module WEMReducePolygons reduces the number of primitives of the input WEM by collapsing edges using a quadric error metric to decide which edges to collapse first.

Details

The edge collapse method collapses an edge so that its former head and tail nodes fall together (and only one of them remains in the mesh). When collapsing an edge, its two adjacent faces are also removed from the mesh.

Each collapse operation introduces an error in the resulting mesh. It is feasible to first collapse those edges that introduce as little error as possible in the resulting mesh. To describe the error introduced, the Quadric Error Metric is used. More information on the topic can be found here.

Tips

For a WEMIsoSurface generated mesh, the reduction percentage can easily be set to 70% without losing geometrical information.

Windows

Default Panel

Input Fields

inWEM

name: inWEM, type: MLBase

The input WEM that needs a reduction in the number of polygons.

Output Fields

outWEM

name: outWEM, type: MLBase

The WEM with the reduced number of polygons.

Parameter Fields

Field Index

Apply: Trigger	isProcessing: Bool	Smooth: Bool
Auto Apply: Bool	Label: String	triangulationMode: Enum
Auto Update: Bool	listenToFinishNotifications: Bool	Use edge length weights: Bool
autoClear: Bool	Modify Attributes: Bool	Use Expert Mode: Bool
Description: String	numEdgeCollapses: Integer	Use face area weights: Bool
editable: Bool	progress: Float	Use node valence weights: Bool
elapsedTime: Float	reduction: Integer	useFaceDiffuseColor: Bool
forwardRepaintNotifications: Bool	Reduction Percentage: Integer	useInputWEMToCreateOutputWEM: Bool
forwardSelectionNotifications: Bool	removePreviousWEMs: Bool	usePolygonOffset: Bool
id: Integer	show: Bool	Vertex Placement: Enum

Visible Fields

Auto Apply

name: autoApply, type: Bool, default: TRUE

If checked, the module will reduce the polygons of the input WEM on any change of a parameter.

Auto Update

name: autoUpdate, type: Bool, default: TRUE

If checked, the module will reduce the polygons of the input WEM if it changes.

Apply

name: apply, type: Trigger

If pressed, the module reduces the number of polygons of the input WEM.

Label

name: label, type: String

Sets a label string stored in the output WEM if Modify Attributes is checked.

Description

name: description, type: String

Sets a description string stored in the output WEM if Modify Attributes is checked.

Modify Attributes

name: modifyAttributes, type: Bool, default: FALSE

If checked, the content of the Description and the Label is stored in the output WEM.

Reduction Percentage

name: targetReduction, type: Integer, default: 70, minimum: 0, maximum: 100

Sets the amount of reduction that is required. The parameter ranges from 0 to 100 percent, although very small and very large reduction rates are not useful.

Smooth

name: smooth, type: Bool, default: TRUE

If checked, the generated mesh will be smoothed.

The resulting error will be a little larger - removing more features - but the quality of the mesh will improve.

Use Expert Mode

name: useExpertMode, type: Bool, default: FALSE

If checked, advanced options are available.

The smooth option corresponds to a middle vertex placement while using the weight factors. Not smoothing corresponds to an optimal vertex placement while not using the weight factors. When the expert mode is used, options can be combined to get a better result.

Vertex Placement

name: vertexPlacementMode, type: Enum, default: Middle

Defines the vertex placement mode.

Although the resulting Quadric Error is clearly larger in the case of Middle placement, the resulting mesh tends to be smoother.

Values:

Title	Name	Description
Optimal	Optimal	New node will be inserted in such a way that the resulting Quadric Error is as small as possible.
Middle	Middle	New nodes are just inserted in the middle between the former head and tail node.

Use face area weights

name: areaWeightedQuadrics, type: Bool, default: TRUE

If checked, edges between triangles with a small area are collapsed first. Uniform face areas are encouraged this way.

Use node valence weights

name: valenceWeightedQuadrics, type: Bool, default: TRUE

If checked, edges with head and tail nodes that have a low valence are collapsed first.

The resulting valence for the new node is valence^head + valence^tail - 2. Overall uniform triangles are encouraged this way.

Use edge length weights

name: edgeWeightedQuadrics, type: Bool, default: TRUE

If checked, edges with a short length are collapsed first. Uniform face areas are encouraged this way.

Hidden Fields

isProcessing

name: isProcessing, type: Bool, default: FALSE

elapsedTime

name: elapsedTime, type: Float, default: 0

id

name: id, type: Integer, default: 0

autoClear

name: autoClear, type: Bool, default: FALSE

removePreviousWEMs

name: removePreviousWEMs, type: Bool, default: TRUE

show

name: show, type: Bool, default: TRUE

editable

name: editable, type: Bool, default: TRUE

useFaceDiffuseColor

name: useFaceDiffuseColor, type: Bool, default: TRUE

usePolygonOffset

name: usePolygonOffset, type: Bool, default: FALSE

listenToFinishNotifications

name: listenToFinishNotifications, type: Bool, default: TRUE

forwardRepaintNotifications

name: forwardRepaintNotifications, type: Bool, default: TRUE

forwardSelectionNotifications

name: forwardSelectionNotifications, type: Bool, default: TRUE

progress

name: progress, type: Float, persistent: no

useInputWEMToCreateOutputWEM

name: useInputWEMToCreateOutputWEM, type: Bool, persistent: no

triangulationMode

name: triangulationMode, type: Enum, default: Strip

Values:

Title	Name
Center node	Center node
Fan	Fan
Strip	Strip

numEdgeCollapses

name: numEdgeCollapses, type: Integer, default: 0

reduction

name: reduction, type: Integer, default: 0