This is not a bug, but an intended behavior. (Well, maybe the bug is that the documentation should be more complete -> changing component to "Documentation".)

The idea in ITK of having different classes for points and vectors is that points change in a different way compared to vectors when being transformed:

• a vector (=direction) does not care about the offset of a transform. Example: let v be a vector pointing to the right (e.g., v=(17,0,0)). Now move it by (0,8,15) ... it will still point to the right (v=(17,0,0), i.e., it did not change at all).
• in contrast, a point (=position in space) does care about the offset. Example: let p be (17,0,0). After moving it by (0,8,15) it will, of course, change to (17,8,15).

BTW itk::Point has a method itk::Point<...>::GetVectorFromOrigin() returning an itk::Vector<...>.

Ok this makes sense. Then we definitely must update the documentation. It is pretty confusing at the moment.
Removed RFD Keyword

(In reply to comment #2)

Ok this makes sense. Then we definitely must update the documentation. It is
pretty confusing at the moment.
Removed RFD Keyword

Shall we add a general chapter on "points" and "vectors" somewhere?

Here are the current documentations of the two methods, which differ only in the word *point* vs *vector*:

IndexToWorld (const mitk::Point3D &pt_units, mitk::Point3D &pt_mm) const
Convert (continuous or discrete) index coordinates of a *point* to world coordinates (in mm) For further information about coordinates types, please see the Geometry documentation.

IndexToWorld (const mitk::Vector3D &vec_units, mitk::Vector3D &vec_mm) const
Convert (continuous or discrete) index coordinates of a *vector* vec_units to world coordinates (in mm) For further information about coordinates types, please see the Geometry documentation.

This might work as either a paragraph or even a subpage of the Geometry Oevrview.

http://docs.mitk.org/nightly-qt4/GeometryOverviewPage.html

Are there more concepts, that many are not aware of which should be added to that documentation?

(In reply to comment #4)

This might work as either a paragraph or even a subpage of the Geometry
Oevrview.

http://docs.mitk.org/nightly-qt4/GeometryOverviewPage.html

Very nice page!

Are there more concepts, that many are not aware of which should be added to
that documentation?

One idea: maybe the pragraph "2. Continuous index coordinates:" should explicitly mention that mitk::Point3D is used as a data type for this (see also T5282 comment #6) and - similar - "3. Index coordinates" might mention that in this case mitk::Index3D is used.

Andreas, as you know the matter, could you document this as well as the continuous problem discussed in T5282 comment #6

New remote branch pushed: bug-9075-UpdateDocumentationForVectorAndPoints

Pushed a version with updated documentation.

[ef19e7]: Merge branch 'bug-9075-UpdateDocumentationForVectorAndPoints'

Merged commits:

2013-10-09 16:11:41 Michael Goetz [ba714d]
Updated documentation to clearify difference between Points and Vectors