[Insight-users] Question about Fast Marching Minimal Path Extraction in ITK

[Olga C Avila-Montes]

Hi Dan!
Thank you very much for your fast reply, the explanation was very helpful. .
.
I *think* I was able to make the changes you suggested by doing the
following:
I changed the second if statement at SpeedFunctionToPathFilter::Execute
from:

       else if ( currentValue >= Superclass::m_TerminationValue )

to:

       else if ( (currentValue >= Superclass::m_TerminationValue &&
		m_Info[Superclass::m_CurrentOutput].HasNextFront())
		|| (currentValue >= m_EndTerminationValue &&
		!m_Info[Superclass::m_CurrentOutput].HasNextFront()) ) 

If I understood correctly, the flag
m_Info[Superclass::m_CurrentOutput].HasNextFront() tells me if we are
tracing a segment to a way point (when it is "true") or if we are tracing to
the end point (when it is "false")
So, I used it to decide if we use the normal Termination Value or the End
Termination Value.

I also added an if in the function SpeedFunctionToPathFilter::GenerateData
that checks whether o not the user input an EndTerminationValue, and if
there is no input, the EndTerminationValue would take the value of
TerminationValue:

       if ( m_WayTerminationValue==NULL )
         {
         m_EndTerminationValue = Superclass::m_TerminationValue;
         }

Now, I have a question:
In the function SpeedFunctionToPathFilter::ComputeArrivalFunction there is a
line that says:

      marching->SetTargetOffset( 2.0 * Superclass::m_TerminationValue );

and with the changes I made, it will always take the normal Termination
Value. Do you think I need to modify this in any way?

Thanks!

-----
Olga C Avila-Montes
Research Assistant, Computational Biomedicine Lab (www.cbl.uh.edu)
Dept. of Computer Science, University of Houston, Houston, TX 77204-3010
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