[Insight-developers] New ITK data objects

[galeotti]

I believe that both of these data structures are sufficiently general 
and unique to justify making them seperate, new parent classes.  I think 
that they should not descend from existing data structures for the 
reasons given below.  Please let me know if my reasons are sufficient 
and valid.  Thanks.

A chaincode is by nature represented as a starting index followed by a 
sequence of local movements into neighboring pixels.  I believe (please 
correct me if I'm wrong) that this is conceptually very different than 
the indented purpose of the PolygonCell and PolygonBoundary classs. 
Also, for efficiency reasons I store and frequently manipulate the 2D 
steps of the chaincode as a single encoded byte.

Although ParametricFunction could syntatically descend from 
SpatialFunction, I believe that it would be very counter-intuitive. 
Parametric funcitons have a single independent variable that is defined 
only over the domain from time = 0 to 1, but the have a multidimensional 
spatial return value (the opposite of "typical" spatial functions).

My current ideal hierarchy of parametric function would be as shown 
below.  What do you all think about making a special class for 2D 
parametric functions?  Efficiently coding parametricfunction for ND 
would be a nightmare, I think (especially for the Fourier smoothed 
chaincode class descendent).

class ParametricFunction<outputtype>  // do-nothing parent class

class ParametricFunction2D<CoordinateType>
     : public ParametricFunction< vnl_vector_fixed<CoordinateType,2> >

class ParametricFunction2DCircle<CoordinateType>
     : public ParametricFunction2D<CoordinateType>
class ParametricFunction2DPolygon<CoordinateType>
     : public ParametricFunction2D<CoordinateType>
class ParametricFunction2DFourierSmoothedChainCode<CoordinateType>
     : public ParametricFunction2D


   I think it makes more sense for chaincode and parametricfunction to 
have their own class hierarchies, but I'd like to hear other developers 
opinions, especially with regard to the reasons I have given.

Thank you,
John

Miller, James V (Research) wrote:
> I guess the first question is how general are these data structures?
> 
> Could some of them use (be? or be if we added something to) the existing
> mesh/cell classes? Is a chain code much different than a polyline of polygon?
> (do you want to represent it as a collection of indexes or as a starting
> index and a neighbor indicator?)
> 
> Could the parametric path classes use or be part of the existing
> function hierarchy? We already have ImageFunction and SpatialFunction.
> Should we have a ParametricFunction? 
> 
> Jim
> 
>>-----Original Message-----
>>From: John M. Galeotti [mailto:jgaleotti@cmu.edu]
>>Sent: Friday, January 10, 2003 1:31 PM
>>To: insight-developers@public.kitware.com
>>Subject: [Insight-developers] New ITK data objects
>>
>>
>> Hello, I'm working with Dr. Stetten at CMU to implement his swath-based
>>  "active contour" as part of ITK. Now that I've isolated the 
>> algorithm from Dr. Stetten's Visualization and Image Analysis 
>> (VIA) toolkit, I'm ready to add it to ITK. In order to do that, I 
>> need to add a couple of data types to ITK, if no one objects. 
>> Comments welcome (and requested).
>> Pseudo-code for the proposed classes follows:
>>
>>class chaincode
>>  get/set origin
>>  add/get step
>>  get number of steps
>>  make 4-connected (convert every diagonal step into 2 
>>orthogonal steps)
>>  get step rotated +/- 45 degrees (optional, but very helpful 
>>for the swath)
>>
>>class parametric path funciton (virtual parent class)
>>  get point at time t (virtual, t lies on the interval [0,1])
>>
>>  class parametric circle
>>  class parametric polygon
>>  class parametric Fourier smoothed chaincode
>>    contstruct from chaincode
>>    get derivative of point at time t
>>    add/set optimum error offset points
>>    get error-corrected point at time t

---
John M. Galeotti   (jgaleotti@cmu.edu)  412-268-9576
Robotics Institute, EDSH, Carnegie Mellon University
5000 Forbes Avenue, Pittsburgh, PA 15213