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

[Elvis Stansvik]

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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