[vmtk-users] Fwd: centerlines question

[Luca A. <an...@ma...>]

> From: Joong-Ho Won <jh...@st...>
> Date: January 22, 2007 10:59:05 PM GMT+01:00
> To: Luca Antiga <an...@ma...>
> Subject: Re: [vmtk-users] centerlines question
>
> Hi Luca,
>
> Thanks again. I understood how it works. So even with a simple Y- 
> shaped branches, I should have 4 cells even though there are 3 groups.
>
> What I am trying to get is to have a unique and robust descriptor  
> for each group, so that I can play with only one centerline in  
> processing individual branch.
>
> I attach a .tgz file for those (failed) files :)
>
> BTW, is it possible to visualize tube surfaces bases on the  
> centerlines and the maximum inscribing sphere radii? That should be  
> a form is distance surface. I would like to see how closely it  
> approximate the original surface obtained by levelsets and marching  
> cubes.
>
> I really appreciate your responsiveness.
>
> Best,
>
>    Joong-Ho.
>
>
> Luca Antiga wrote:
>> Hi Jong-Ho,
>>   glad you're being successful with your analysis.
>> First a suggestion: if you need to spit out your data in a CSV- 
>> like format, you can use the pointdata format. You can do it by  
>> naming your output file with a .dat extension.
>> As to centerlines and branches, you're right, in general there's  
>> more than one cell per branch. If you look at the pictures of the  
>> branch splitting tutorial (http://villacamozzi.marionegri.it/~luca/ 
>> vmtk/doku.php?id=vmtk:vmtk_tutorials:branch_splitting) you can  
>> figure out why: each vmtk centerline is defined from an inlet to  
>> an outlet. If you have a single bifurcation, the upstream branch  
>> will be defined by both cells corresponding to the two  
>> centerlines, while the downstream branches will be made up by one  
>> cell each. The two cells of the upstream branch are mostly  
>> coincident, except in the bifurcation region. How early and how  
>> much they depart depends on the shape of the bifurcation region.
>> This is a feature that's very useful in handling complex branching  
>> situations, and it's the basis of geometric analysis of  
>> bifurcations. However, I also understand that one may want to have  
>> a unique definition... let me know what you have to do with your  
>> coordinates, I can maybe help out.
>> Anyway, in order to find out which cells belong to which branch,  
>> you can use the GroupIds array (refer to the tutorial for an  
>> explanation).
>> If you need to extract points at the same abscissa at every cell  
>> of a branch, run centerlines through vmtkcenterlineattributes,  
>> which will compute abscissas along centerlines. If you run it  
>> before splitting and then split branches, abscissas will start at  
>> zero at the inlets, and then progress along every branch. If you  
>> run it after splitting, every branch will start at zero. Once you  
>> have the abscissas, every cell with the same group id will have  
>> correspondent points at the same abscissas (Now that I think about  
>> it, vmtk should have a filter that uses this criterion to generate  
>> a "one cell per branch" version of centerlines).
>> Let me know what's your purpose, so I can be more specific.
>> A last point: for some reason your vtp attachments are embedded in  
>> messages and I can't save them properly. Could you please first  
>> zip them and then attach?
>> Cheers
>> Luca