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Finite Element Analysis Toolbox
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geom_decompose.m File Reference

Description

GEOM_DECOMPOSE Analyze and decompose geometry.

[P,E,F,V,IP] = GEOM_DECOMPOSE( GEOM, TOL, IS_ANALYZED ) Decomposes the geometry struct GEOM into unique points/vertices P, edges/line segments E, faces or surfaces F, and volumes V (for 3D geometries). IS_ANALYZED (default false) indicates if the geometry has already been processed by GEOM_ANALYZE. The optional input argument TOL defines the tolerance for deduplication and zeroing vertex coordinates (default eps*1e3). IP indicates which vertices in P are due to point geometry objects (and not part of edges, faces, or volumes).

Geometries consisting of multiple geometry objects will be analyzed and if required split into separate non-overlapping objects. The decomposition process tries to apply one intersection and two subtraction operations to each combination of two geometry separate objects.

The output argument P is a array of unique points/vertices of size (n_p,n_sdim).

The two last columns of the edge/line segment array E (size (n_e,3)) contains start and end indices to vertices in P that make up the edges. The first column indicates edge segment groupings (corresponding to boundaries in 2D and geometry edges in 3D, No defined edge grouping is indicated with zeros in 3D).

The face/surface array F of size (n_v,2+n_max_e) consists of indices to edges that make up the faces (a negative entry indicates reversed edge direction). Similar to the first column of E, the first column of F also indicates face groupings (integer > 0). The second boolean column indicates if each face is an outer boundary (0) or a hole (1). For faces with less than n_max_edges (the maximum number edges in any face) the extra entries are padded with zeros.

The volume array V (for 3D) indicates which faces F constitutes the volumes (size n_v,2+n_max_f) where a negative entry also here indicates reversed face direction. Similarly to F, the first column specifies the volume group, and the second if the entry volume describes the outer (external) or inner volume boundary (hole).

See also
gobj_decompose, geom_analyze