[Camino-users] RE: subsetpoints output

[Ferizi, Uran]

Until you get a better answer ...

1) whatever subset you get out of Camino, it will not be a unique one (depending on the first direction that you pick; in fact, there may be 60_Choose_30 subset combinations of directions --- this is important if, say, you want to keep the signal in the z-axis ...); or,

2) the first 30 directions in the list may actually be the ones you're after --- I believe they are listed so that if a scan is interrupted, the sampled directions would form a self-contained shell; or,

3) you can design your very own shell of 30 dirs. by picking the first direction you like from the 60-shell, and eliminating its closest vector, then pick the next closest and eliminate its neighbour, and so on (via arccos of the dot product --- this is after all Coulomb's law, which is how the "minimisation of electrostatic repulsion" is based on, no?);
--- or you could even employ the 30 directions from Camino's PointSet, and find the closest vector of the 60-shell to each of the 30-shell (again, two loops on Matlab?).

Uran
PS: But it sounds a little dodgy that all that calculation is taking 5h ... even if it churned out all the subset combinations, it should be faster.



________________________________
From: Grussu, Francesco
Sent: 19 August 2013 7:59 PM
To: Ferizi, Uran; camino-users at www.nitrc.org
Subject: RE: subsetpoints output

Thanks for that.

However my directions do have to be part of the initial 60 direction set, regardless how  good or not it is.
This initial 60 direction set is something I was given with and I have real measures associated to it. Therefore I cannot change those.

I just wondered how to interpret the outputs of subsetpoints .

Regards
Francesco

________________________________
From: Ferizi, Uran
Sent: 19 August 2013 19:48
To: Grussu, Francesco; camino-users at www.nitrc.org
Subject: RE: subsetpoints output

Use Camino's point sets --- you have all the directions (well, from 3 to 256, and 755) ready for you. T
In a terminal window, do:
ls -l camino/PointSets (to obtain the full list Elec003.txt and so on).

Is this what you wanted?

________________________________
From: camino-users-bounces at www.nitrc.org [camino-users-bounces at www.nitrc.org] on behalf of Grussu, Francesco [francesco.grussu.12 at ucl.ac.uk]
Sent: 19 August 2013 7:34 PM
To: camino-users at www.nitrc.org
Subject: [Camino-users] subsetpoints output

Dear Camino team,
I am currently trying to select a subset of 30 directions from a set of 60 directions. I would like to get the combination of 30 out of 60 directions which is the most uniform possible. Therefore,  I adopted the command subsetpoints.

My code, which I run on the input file inputDirs.bvec (a text file with 60 rows, 3 colums, one row per direction)  is something like


cat inputDirs.bvec | subsetpoints -singlesubset 30 -savestate myCurrentState > outputdirs.bvec


and after  ~ 5hours of processing, it returns the output outputdirs.bvec and a second file called orderedPoints.dat .

For what I understood from the guide, I think that both first 30 rows of orderedPoints.dat  and rows from the 2nd to 31st of outputdirs.bvec are the subset of directions I am looking for. Can you confirm this?

Overall, first 30 rows of orderedPoints.dat  and rows from the 2nd to 31st of outputdirs.bvec are the same points but ordered differently. What's the difference between the two orders?

Thanks a lot for helping me out,
all the best

Francesco


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