[vtkusers] getting pointids from an imagedata

Tue Jul 10 09:47:12 EDT 2001

Hi John,

thanks for your mail. I tried to validate my pointIds by setting the scalar
as you mentioned. The painting itself worked, but it turned out that my
pointId isn't pointing to the right pixel. In most cases we can't even find
a pointId (return -1).

We tried to get the pointId using the method vtkImageData.FindPoint(x,y,z)
using "normal" pixel-coordinates like 0,0,0 / 10,10,0 / 127,127,0 ...

We know that there definitly should be some pixels on these positions. How
would you get the pointId for a point where you have the
userinterface-coordinates. Furthermore the displayed image could be rotated
by the user. So we cannot make any assumptions about the position of the
axes.

I think picking the point from the userinterface should be possible because
in my opinion the Renderer always knows which pixel to paint even if the
image is rotated / zoomed or something else.

It would be great if you have any ideas,

matt

----- Original Message -----
From: "John Biddiscombe" <jbiddiscombe at skippingmouse.co.uk>
To: "Matthias Zangl" <zangl at ism-austria.at>; <vtkusers at public.kitware.com>
Sent: Tuesday, July 10, 2001 1:44 PM
Subject: Re: [vtkusers] getting pointids from an imagedata

> You'll also need to
> > >
imagedata->GetPointData()->GetScalars()->SetScalar(mydubiousPointID,255)
> then
> imagedata-Modified to make sure the renderer forces a full update
>
> By offset and Scaling I simply mean that if the origin (of the image) is
at
> x,y then pixel 1,1 is at some x,y offset and the rest follow.
>
> JB
>
>
> At 10:37 10/07/2001, Matthias Zangl wrote:
> >Hello John,
> >
> >thanks for answering my questions. I am using a renderwindow. Its
actually a
> >self-written imageviewer by using the Actor2D and setting the origin.
> >
> >I've the x y coords from the mouse click.
> >
> >I tried them to convert it with setdisplaypoint, displaytoworld and then
get
> >the worldpoint. Maybe thats the wrong way of conversion?
> >
> >Could you give me more details / infos on what you mean by computing the
> >pixel location from origin + offset and scaling?
> >
> >Well, its very helpful for me to set the scalar so that I can see whether
my
> >point is the correct one...
> >
> >Matt
> >----- Original Message -----
> >From: "John Biddiscombe" <jbiddiscombe at skippingmouse.co.uk>
> >To: "Matthias Zangl" <zangl at ism-austria.at>;
<vtkusers at public.kitware.com>
> >Sent: Tuesday, July 10, 2001 11:04 AM
> >Subject: Re: [vtkusers] getting pointids from an imagedata
> >
> >
> > > Matt
> > >
> > > I'm not sure I'm able to help you really. There are so many details of
how
> > > you are displaying your image data (renderwindow or imagewindow -
> > > drawpixels or imageactor) if you're using an imagewindow then I never
> >touch
> > > them so can't help, they may not implement the worldpoint-displaypoint
> > > features in the same way as the renderwindow. Check also that the
slice
> > > number you're using is being set into your SetDisplayPoint(x,y,lastY)
> >call.
> > > I generally do something like this
> > >
> > > MouseClick->
> > >    Get X,Y coords
> > > Compute pixel location from origin+offsetx/y and scaling
> > >    pointID follows,
> > > but as I mentioned in an earlier post last week I think, I don't use
an
> > > imagewindow and have implemented all the image display code myself
from
> > > scratch - this means I know exactly where pixel 0,0 is etc etc and
there
> > > are no problems. I'm afraid you're going to have to use a lot of trial
and
> > > error but if you do have a dataset and want to see if the pixel you've
got
> > > is correct, the easiest way is probably
> > >
imagedata->GetPointData()->GetScalars()->SetScalar(mydubiousPointID,255)
> > > or something along those lines. Then it should change colour and you
can
> >at
> > > least test it - n'est pas?
> > >
> > > JB
> > >
> > > At 14:59 09/07/2001, Matthias Zangl wrote:
> > > >Hello John,
> > > >
> > > >I tried out your suggestion and I am not clear, if everything is
working
> > > >properly:
> > > >
> > > >float worldPoint[4];
> > > >
> > > >  this->GetRenderer()->SetDisplayPoint(x,y,lastY);
> > > >  this->GetRenderer()->DisplayToWorld();
> > > >  this->GetRenderer()->GetWorldPoint(worldPoint);
> > > >
> > > >  int pointId =
> >data->FindPoint(worldPoint[0],worldPoint[1],worldPoint[2]);
> > > >
> > > >  float coord[3];
> > > >  data->GetPoint(pointId,coord);
> > > >
> > > >The function FidnPoint seems to return a valid pointId (although the
> > > >worldPoint-coords are not very familiar for me (0.001....)). But at
least
> >I
> > > >am getting a pointId. For checking if its valid I tried to get the
coords
> > > >from the point id (with getpoint). But the coords stored in the
> >coord-array
> > > >are always 0,5 or -0,5 for all axes.. There should definitly be a way
for
> > > >transforming them to useful coordinates,right?
> > > >
> > > >Is there another way for doing something with my point for ensuring
that
> >I
> > > >got the right one?
> > > >
> > > >thx,
> > > >Matt
> > > >----- Original Message -----
> > > >From: "John Biddiscombe" <jbiddiscombe at skippingmouse.co.uk>
> > > >To: "Matthias Zangl" <zangl at ism-austria.at>;
> ><vtkusers at public.kitware.com>
> > > >Sent: Saturday, July 07, 2001 12:25 PM
> > > >Subject: Re: [vtkusers] getting pointids from an imagedata
> > > >
> > > >
> > > > > Sorry, I misread your request. You'll need to get the
window->World
> > > > > coordinate conversion from
> > > > > vtkViewPort::DisplayToWorld
> > > > > and then use findpoint...
> > > > >
> > > > >
> > > > > At 15:29 06/07/2001, John Biddiscombe wrote:
> > > > > >vtkDataSet::
> > > > > >int FindPoint (float x, float y, float z)
> > > > > >int FindPoint (float x[3])
> > > > > >
> > > > > >all subclasses (ImageData) implement it and given a 3space
> >coordinate,
> > > >you
> > > > > >can find the point ID of the one you want.
> > > > > >
> > > > > >JB
> > > > > >
> > > > > >
> > > > > >At 14:16 05/07/2001, Matthias Zangl wrote:
> > > > > >>Hello!
> > > > > >>
> > > > > >>I am displaying a volume (vtkImageData) - slice by slice on my
> >screen. I
> > > > > >>realized it by changing the outputorigin on slicing. Well, that
> >works
> > > >well
> > > > > >>so far. Now I want to get the pointid from a point the user is
> >selecting
> > > >on
> > > > > >>the screen. All I got are the coordinates in the renderwindow. I
> >suppose
> > > > > >>I've to take care that they 're calculated dependend on the
> >resolution
> > > >and
> > > > > >>current zoomfactor of my image. Maybe someone have some hints
for
> >me.
> > > > > >>
> > > > > >>greatly appreciated,
> > > > > >>
> > > > > >>bye,
> > > > > >>Matt
> > > > > >>
> > > > > >>
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