[Insight-users] Problem with Fast marching minimal path extraction

[Maria Alejandra Zuluaga Valencia]

Hi Dan,

In order to provide you more information I did a small modification to the SpeedFunctionToPathFilter. I have added an image writer so that I can save what you call the current arrival function. At the same time, I compare the result with a well-known toolbox in matlab that performs the fast marching (btw, this is my final purpose; using itk instead of matlab). What I found is that the arrival functions differ significantly (might the problem be on the Fastmarching itself?). Moreover, I do obtain a path in matlab, no matter the end point.

To illustrate you the situation I provide you screenshots of the matlab results (example_D_one_.jpg and example_path_one.jpg files) and the arrival function with itk (example_D_two.jpg), since no path is obtained. For this example, I have used an image of mine. I was using your Synthetic-04-Speed to evaluate  the filter, but I can't not read zraw in matlab, so that is why I send you this other example. However, I will try to solve the zraw problem so that I can run the matlab code in Synthetic-04-Speed.

Regarding your saying about the path, perhaps on an image as Synthetic-04-Speed there should be no path when a point is badly placed (due to the completely dark background) but, in the image as the one I am using I think it should get something (as in matlab). I am not an expert but I believe that one of the advantage/disadvantage of minimal paths approaches is the fact that it will always find a path given two points. But, as I said before, according to the results I am sending you, I believe the problem seems to come from the arrival function and not from the path search. What do you think?

Since my firewall does not allow me to attach files to emails, you can obtain the screenshots here: http://www.creatis.insa-lyon.fr/~zuluaga/fm_issues/

regards,

Maria

ps. If you want I can also send you the image of my examples, while I solve the zraw problem. It is very small (184x184x23). I could place it on my server.

 let me know if that sounds ok.









________________________________
De: Dan Mueller <dan.muel at gmail.com>
Para: Maria Alejandra Zuluaga Valencia <mariazulv at yahoo.es>
CC: "insight-users at itk.org" <insight-users at itk.org>
Enviado: miércoles 6 de julio de 2011 14:43
Asunto: Re: [Insight-users] Problem with Fast marching minimal path extraction

Hi Maria,

Can you please provide some more information?

Which synthetic image are you using? Where are you placing the seed point?

I would not expect that every seed point will work -- the seed point
needs to be in a region which is reachable by the Fast Marching
expanding front. For example, placing the seed point in a region with
low speed (near 0.0) will not work.

Attached are a few examples using different seed points.

Regards, Dan

On 5 July 2011 17:23, Maria Alejandra Zuluaga Valencia
<mariazulv at yahoo.es> wrote:
> Hi,
> I am trying to use the minimal path extraction algorithm reported in:
> http://hdl.handle.net/1926/1332
> After some minor compilation errors I managed to make it work. However, I
> found the behavior is a bit weird. As an example:
> if I test with one of the Synthetic images provided and the path points
> given, everything works fine. But, as soon as I change one of the path end
> points it stops working. By stop working I mean that the extracted path
> contains no points. I've tried with several examples and it is always the
> case.
>
> As far as I know, no matter how bad I place my end point, I should get a
> minimal path connecting the end and start points. Has any one had the same
> kind of problem? did you managed to fix it?
> thanks,
> Maria
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