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Cleaning geometries

Last post pe, loka 31 2008 15:48 by RicardoVelez. 0 replies.
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  • pe, loka 31 2008 15:48

    Cleaning geometries

    Cleanup geometry imported from CAD or similar system. Geometry might include following cases:

    1. Geometry is in wrong scale or in wrong orientation

    -> SCALE Single geometry or NODE/FEATURE structure geometries
    -> ROTATE & TRANSLATE geometry to right orientation or/and to position
    -> ORIGIN Defining

    Scale, rotate and translate one geometry feature content
    Scale, rotate and translate complex feature tree

    1.1. Scale

    Create a transform feature under the geometry. Sx(100).Sy(100).Sz(100) expression will scale all directions by 100.

    1.2. Rotate & Translate

    Rotate & Translate component geometry feature (not the component) to align and position it correctly

    2. Geometry meshes are structured in a non-optimized manner

    a) Geometry is one continous mesh with no logical parts

    select the correct geometry feature and then switch to the Geometry sets filter. Select on geometry set and right mouse click to open the menu

    -> Merge boundary points (tolerance)
    -> Decompose geometry set

    b) Geometry is constructed using many, non-sharing parts

    This is typical with some CAD systems that they export all roundings etc as separate meshes
    Same can happen with VRML import, where geometry might not use point sharing at all.

    -> Select one mesh, and then grow selection meshes with same material
    -> Merge sets with same material
    -> Merge boundary points (tolerance)
    -> Decompose geometry into the logical meshes

    NOTE: When geometry is merged using boundary points, some geometries become smooth due crease angle
    even when they should not. In these cases decrease crease angle to 30 or do not merge boundary points.

    NOTE: Intelligent merge boundary points algorithm, which does not merge points, which

    c) Geometry is corrupted or not clean

    -> Remove all duplicate geometry (in same set or in duplicate set, quilts)
    -> Cleanup all collapsed polygons
    -> Autoreverse surface polygons to have unified surface direction

    3. Geometry is heavy


    -> Remove holes
    -> Blockify/Cylinderify
    -> Remove small details
    -> Remove occluded details (features/geosets/polygons). Automatic occlusion test could use ambient occlusion or offline render test.
    -> Clean heavily tesselated simple (planar) surfaces
    -> Decimate
    -> Retesselate surfaces (verify that surface boundaries are tesselated

    4. Feature (Node) structure is too complex for editing

    -> Collapse levels together to make editing easier (this optimizes also rendering and memory consumption)

    Ricardo Velez
    Research and Development Manager
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