[vtkusers] vtkDataSet::FindPoint, vtkExtractVOI and world coordinates?

[Elvis Stansvik]

Den 7 sep. 2016 3:32 em skrev "Cory Quammen" <cory.quammen at kitware.com>:
>
> Elvis,
>
> Have a look at vtkImageData::FindPoint(double x, double y, double z).
>
> It takes into account the image spacing and origin, but will not
> correct for any modifications to the position of the vtkVolume you
> seem to be using to represent it in the scene.

Thanks Cory,

I did initially find FindPoint, but I was unsure how I can translate the
vtkIdType it returns (some sort of index?) into i,j,k voxel coordinate. Do
you know?

Since then I've also found  vtkImageData::ComputeStructuredCoordinates,
which looks similar, but does seem to produce a ijk voxel coordinate.
Perhaps that is the function I'm looking for? It's doubly interesting since
it has a static variant where I can specify the origin, spacing etc
manually, which I might have a need for actually, if I want to do the same
computation but don't have access to an actual vtkImageData instance, only
its parameters so to speak.

Elvis

>
> HTH,
> Cory
>
>
>
> On Wed, Sep 7, 2016 at 3:10 AM, Elvis Stansvik
> <elvis.stansvik at orexplore.com> wrote:
> > Den 4 sep. 2016 2:25 em skrev "Elvis Stansvik"
> > <elvis.stansvik at orexplore.com>:
> >>
> >> Hi all,
> >>
> >> I have multiple volumes in a renderer, positioned above/below each
other
> >> (like a "string" of volumes) along the Z axis, none of them are
> >> intersecting. As the user clicks+drags the mouse in the viewport, I
need to
> >> capture the mouse position at the start/end positions of the drag
operation
> >> and convert them to world coordinates. I think I have these parts
figured
> >> out.
> >>
> >> Then, I need to search through the list of my volumes (sorted by their
end
> >> positions in world coordinates), and construct a series of
vtkExtractVOI
> >> that will extract the selected segments. For volumes that are
completely
> >> inside the selected area, the vtkExtractVOI will extract the full
volumes,
> >> but for the start/end volume (which may be the same volume), it will
only
> >> extract a portion of it.
> >>
> >> I looked at the vtkDataSet::FindPoint, which I think will give me a
linear
> >> point ID (not familiar with that from before) for a point given in
world
> >> coordinates. But how can I convert that to a structured point position
that
> >> I can use when setting up the extent to use for my vtkExtractVOI?
> >>
> >> Is the static vtkStructuredData::ComputePointStructuredCoords helper
the
> >> function I'm looking for? Or is there some other easier way to extract
an
> >> area of a volume when the area is expressed in world coordinates?
> >> (specifically, as a start/end Z position in world coordinates).
> >>
> >> Here's an ASCII drawing that perhaps explains better what I want to do,
> >> the rectangular areas are my volumes:
> >>
> >> ^  +-----+
> >> |  |     |
> >> |  | P1  |  <--- User clicks here (world coordinate X, Y, Z)..
> >> |  |     |
> >> Z  +-----+
> >>    +-----+
> >>    |     |
> >>    |     |
> >>    +-----+
> >>    +-----+
> >>    |     |
> >>    |     |
> >>    |  P2 |  <--- ..and drags to here (world coordinate A, B, C).
> >>    |     |
> >>    |     |
> >>    |     |
> >>    +-----+
> >>
> >> From this I want to create three vtkExtractVOI, that when combined
gives a
> >> list of vtkImageData that represents the selected area along the Z
axis (in
> >> the X and Y direction, everything from the volumes should be included).
> >>
> >> Thanks in advance,
> >> Elvis
> >
> > I realized my mail above is a little long-winded and unclear. Sorry
about
> > that. In essence, what I'm asking is how to map an x,y,x (double) point
in
> > world coordinates to a i,j,k (int) grid position (voxel coordinate) of a
> > given volume. I don't want the nearest point, but to return "null" or
> > equivalent if the world point does not fall inside any voxel.
> >
> > I'd also be interested how to do the same but against a plain
vtkImageData
> > instead of a vtkVolume. For this I assume I'd have to provide some info
> > about where in the world the vtkImageData belongs (where/how I intend
to map
> > it into the scene).
> >
> > Anyone know what the VTK API for this is?
> >
> > Thanks in advance,
> > Elvis
> >
> >>
> >>
> >
> >
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>
>
> --
> Cory Quammen
> Staff R&D Engineer
> Kitware, Inc.
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