[IGSTK-Developers] Continuting the discussion on error handling methods....

[Andinet Enquobahrie]

David,

Thank you for the practical insight. We first thought that image and 
tracker landmark establishment would alternate. I will have to modify 
the state machine design in the LandmarkRegistration class to make it 
less restrictive .

-Andinet

> Hi Andinet,
>
> For landmarks: For image-guided surgery, the user will usually set the 
> positions of all the landmarks before doing any tracker measurements.  
> In fact, to save time, I always set the landmarks before I even 
> wheeled the computer into the OR, so that the only thing the surgeon 
> had to do was measure the landmark positions with the Polaris.  I 
> think the error-checking should be done when the transformation is 
> calculated, not when the landmarks are set.  This also helps to 
> centralize the error checking, since you also need to check the RMS 
> residual of the point fit, as well as minumum number of points when 
> the transform is calculated.
>
> Also: when in the operating room, it often occurs that one of the 
> doughnut fiducials either falls off or ends up in a position 
> inaccessible to the tracker.  This can easily happen after the 
> fiducial has been located, but before the tracker has been used to 
> measure its position.  There has to be a way to either delete such 
> fiducials from the list, or better, to mark them as "ignored" since 
> deleting them from the list will disrupt the numbering of the fiducials.
>
> Rule #1 of the operating room: you need to be prepared for anything 
> that might go wrong!
>
>
> About error checking:
>
> To ease the burden of error checking, I think that we need macros or 
> some other shortcut to convert state-machine inputs to IGSTK Events 
> and vice-versa.
>
> For example, we need a concise way to state, in code, the following:
> 1) when we receive input A while in state B, event C will be generated 
> and we will end up in state D
> 2) when object A produces event B, send input C to our state machine
> If we had macros for the above, I think that event-based 
> error-handling code would be easier to write.
>
> - David
>
> Andinet Enquobahrie wrote:
>
>> Dear all
>>
>> I am putting the final touches on the LandMarkRegistration and 
>> ImageReader classes implementation for iteration 6. The main loose 
>> end I need to tighten up is error handling. Although we have 
>> brainstormed several options for error handling , we haven't yet 
>> reached a consensus. If you would like to refresh your mind on this 
>> topic,  please refer to the wiki page that David put together.
>>
>> http://public.kitware.com/IGSTKWIKI/index.php/Error_Handling#Kinds_of_Errors 
>>
>>
>> For my specific needs, I am planning to implement event observers for 
>> recoverable error conditions in landmark registration and image reading.
>>
>> The recoverable error conditions that I am anticipating are the 
>> following.
>>
>> For LandMarkRegistration class
>>
>> 1) A request for transform computation before "enough" number of 
>> landmarks are established.
>>
>> 2) Incorrect order of landmark establishment.  I am enforcing a 
>> specific order of landmark establishment i.e  image followed by 
>> tracker coordinate for landmarks 1,2,3 (We are using 3D Rigid body 
>> transform)  For example, an error condition arises if the application 
>> sets image coordinates of two landmarks successively without setting 
>> the tracker coordinate of the first landmark.
>>
>> For ImageReader classes
>>
>> 1) An image read request before specifying the image file name.
>> 2) Error during image reading operation (may be corrupted image data, 
>> invalid image format etc..)
>>
>> This is not an exhaustive list by any means. But I believe these are 
>> the major ones.
>>
>> I would like to get your comments/thoughts/suggestions on
>>
>> - additional major error conditions and
>> - my pick of an error handing method
>>
>> thanks
>>
>> -Andinet
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
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>
>
>