VLFLregions

by Tim C. Lueth, SG-Lib Toolbox: SolidGeometry 5.6 - Surfaces
Introduced first in SolidGeometry 5.1, Creation date: 2021-07-27, Last change: 2025-09-15

fnct to separate regions in face index list

Description

This is the modern version of VLFLseparate. It is used for instance in FSofSGnormal.
Following the terms of Matlab in the polyshape classe, I now also use the term regions for surfaces that are connected to each other. In previous versions, only the term VLFLseparate or SGseparate was used. Based on FLorder

See Also: SGseparate , SGsurfaces , FLorder

Example Illustration

Syntax

fil=VLFLregions(VL,FL,[FIL])

Input Parameter

`VL`:		Vertex list
`FL`:		Facet list
`FIL`:		ONE facet index list; default is 1:size(FL,1)

Output Parameter

fil: cell list for separated regions

Copyright 2021-2025 Tim C. Lueth. All rights reserved. The code is the property of Tim C. Lueth and may not be redistributed or modified without explicit written permission. This software may be used free of charge for academic research and teaching purposes only. Commercial use, redistribution, modification, or reverse engineering is strictly prohibited. Access to source code is restricted and granted only under specific agreements. For licensing inquiries or commercial use, please contact: Tim C. Lueth

Algorithm (Workflow)

This function, VLFLregions, is designed to separate regions in a face index list. It is a modern version of VLFLseparate and is used in the context of surface geometry processing.

Input Parameters

VL: Vertex list, which contains the coordinates of vertices.
FL: Facet list, which contains indices of vertices forming each facet.
FIL: Optional facet index list. If not provided, it defaults to 1:size(FL,1), meaning all facets are considered.

Output

fil: A cell list containing separated regions, where each cell corresponds to a region of connected facets.

Algorithm Steps

Initialize FIL using getfuncparams to handle optional input, defaulting to all facets if not specified.
Extract the subset of facets FLS from FL using the indices in FIL.
Order the facets using ELorder, which returns FLN (ordered facets) and SIL (start and end indices of regions).
Map the rows of FLS to FLN using maprows to get the mapping indices b.
Determine the number of regions nf from the size of SIL.
Initialize fil as a cell array to store each region.
For each region k from 1 to nf:
- Extract the range of indices from SIL and map them back to the original facet indices using b.
- Store the mapped indices in fil{k}.
If no output is requested (nargout==0), plot the regions:
- Use SGfigure to set up the figure.
- Plot all facets with a low alpha value using VLFLplotalpha.
- Iterate over each region and plot it with a distinct color using colofn to select the color.

Algorithm explaination created using ChatGPT on 2025-08-19 06:51. (Please note: No guarantee for the correctness of this explanation)

Last html export of this page out of FM database by TL: 2025-09-21