[IGSTK-Developers] Follow up: an igstkReferenceCalibration class?

[David Gobbi]

Hui Zhang wrote:

> Hi, all,
>
> As we find that the igstkPivotCalibration can only give 3D translation 
> in the output transform, which is limited by the pivot routine, so 
> should we have a general igstkReferenceCalibration to get the 3D/5D/6D 
> transform?

It looks like we should adopt a naming convention that includes "Tool" 
as part of the name, to make it clear that the transform is to be used 
as a ToolCalibrationTransform:

igstkPivotToolCalibration, igstkReferenceToolCalibration

> The idea of igstkReferenceCalibration class is to compute the 
> reference calibration transform from one or more object points (can be 
> 3D/5D/6D) to another refrence point ( can also be 3D/5D/6D).

I'm not sure what you mean by a 5D or 6D reference point, since a 
"point" is always 3D.  Some of the scientific literature, especially in 
computer graphics, uses the term "pose" to describe the position and 
orientation of an object together.  When you say a 5D or 6D point, do 
you mean a 5D or 6D position/orientation transform returned by the 
tracker? 

> The genreal diagram will be:
> Input:                                Output:
> object point->ref point
> 3D->3D                            3D translation
> 3D->5D                            3D translation
> 3D->6D                            3D translation
> 2x3D->3D                        3D translation
> 2x3D->5D                        3D translation + 2D rotation
> 2x3D->6D                        3D translation + 2D rotation
> 5D->3D                            3D translation
> 5D->5D                            3D translation + 2D rotation
> 5D->6D                            3D translation + 2D rotation
> 6D->3D                            3D translation
> 6D->5D                            3D translation + 2D rotation
> 6D->6D                            3D translation + 3D rotation
>
> Some further conditions is: 2x3D = 5D, 3x3D = 6D, 2x5D = 6D, ...
>
> So, in our tool calibration routine, we can get first 3D point from 
> igstkPivotCalibration, and then set second hip point as the input 
> together, 2x3D->5D to get the 3D translation + 2D rotation. For 
> example, in the PivotCalibration, we get (x, y, z) from the tip, and 
> then we can set (x, y, z + 100) as the hip's translation. Those two 
> points (x, y, z) (x, y, z + 100) will input to 
> igstkReferenceCalibration to get the final igstkTransform. In this 
> case, the default reference point is (0, 0, 0). If we input the 
> run-time positions as input, such as T * (x, y, z)', T * (x, y, 
> z+100)', we also need input the reference point which build that T 
> transform to get the final calibration result.

This sounds good.

> There is a small problem with:
> 5D->5D                            3D translation + 2D rotation
> 5D->6D                            3D translation + 2D rotation
> in those two cases, we get the same 5D output, but only in 6D 
> reference we can the correct referenced position, Needle is a specific 
> shape, for we assume it has a translation like (0, 0, z) so that it 
> can eliminate the 6th rotation error which will propogate along x and 
> y axies.

I think that I follow what you're talking about here.  Tools like 
needles really are only 5D, so only a 5D calibration is necessary for 
these tools.  We don't need a 6D calibration: the third orientation 
angle is arbitrary.  This also implies that the spatial objects for 
these tools must be radially symmetric, e.g. cylindrical.

 - David

> Regards,
> James
>
> ----- Original Message ----- From: "David Gobbi" <dgobbi at atamai.com>
> To: "Patrick Cheng" <cheng at isis.georgetown.edu>
> Cc: "'IGSTK-developers'" <igstk-developers at public.kitware.com>
> Sent: Wednesday, November 30, 2005 2:38 PM
> Subject: Re: [IGSTK-Developers] SpatialObject calibration transform
>
>
>> Hi Patrick,
>>
>> Thanks for the summary.  The reason that I would prefer to add the 
>> orientation as part of the tool calibration transform is that I think 
>> we should keep the number of coordinate transformations in IGSTK to a 
>> minimum.
>>
>> Each coordinate transformation is a possible source of error.  Even 
>> worse, if two different transformations can be used to achieve the 
>> same result (e.g. a tool calibration transform and a spatial object 
>> calibration transform), then both transforms can have errors that 
>> cancel each other out.  These sorts of errors can be very hard to debug.
>>
>> I think the best solution is if the ToolTipCalibration class has a 
>> method that allows you to specify the orientation of the tool that is 
>> being calibrated.
>>
>> - David
>>
>> Patrick Cheng wrote:
>>
>>> Hi everybody,
>>>
>>> What I was trying to say in the Tcon is:
>>>
>>> the cylinder object (longest axis) is align with Y axis in image 
>>> space (inherited from ITK by default). while the probe is aligned 
>>> with the tracker's X axis.
>>>
>>> So when we get the PatientTransform, which essentially align the 
>>> image space and tracker space together, but still the cylinder 
>>> spatialobject and the probe is not aligned correctly. We need first 
>>> rotate our spatial object to align with the probe, and then use the 
>>> pivot calibration transform to get the tip translation.
>>>
>>> This adjustment of the spatial object's coordinate system, can be 
>>> done by adding the rotational information to tool calibration 
>>> transform. or we can add it to a upper level transform when we 
>>> construct a spatial object group to model the probe.
>>>
>>> Patrick
>>
>>
>>
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>
>
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