[vtkusers] Probing unstructured point data onto an unstructured grid

[Alex Lennon]

Hi Prabhu,

Sorry if the mail was unclear.

>>2. The points in your brick_8.ipr do not coincide with the points in
>> brick_8.vtk.  Is this what you want?

The 'ipr' file contains the finite element integration points. These are
simply interpolated points inside a finite element at which numerical
integration is performed (this is why they do not coincide with the points
in the 'vtk' file). All quantities are calculated at these points and not at
the nodes of the element (vertices of the cell in the 'vtk' file).

>>1. brick_8.ipr defines no volumes and only points.  Probing with this
>> will only give you the values at these points.  Visualizing these
>> points will not be any fun, you'll just see a bunch of tiny coloured
>> points.  If you want to probe the volume then you need to probe with
>> another volume.

The point data in the 'ipr' file already contains the results---what I'd
like to do is to interpolate from the point data in the 'ipr' file to the
nodes of the 'vtk' file (i.e. the reverse of the above). I have written code
to do this before writing out the vtk file from my finite element
application but I would like to be able to do this when selecting different
subsets of integration points as I visualise the data (e.g. based on
material properties of the finite element model).

I tried vtkPointDataToCellData but it still gave 0's. Anyway, it's the
points making up the cell in the 'vtk' file that I would like to map the
data to. If a probe filter is not the correct way of going about this I'd
appreciate any suggestions as to what is.

Thanks for the help,

Alex

Trinity Centre for Bioengineering
Dept. Mechanical Engineering
Trinity College
Dublin 2
Ireland

email: alennon at tcd.ie
Tel:   +353-1-608 2396
Fax:   +353-1-679 5554
http://www.biomechanics.ie

-----Original Message-----
From: Prabhu Ramachandran [mailto:prabhu at aero.iitm.ernet.in]
Sent: Wednesday, November 13, 2002 7:07 PM
To: Alex Lennon
Cc: Vtkusers
Subject: Re: [vtkusers] Probing unstructured point data onto an
unstructured grid


>>>>> "AL" == Alex Lennon <alennon at tcd.ie> writes:

    AL> Hi, I'm using vtk to visualise results of finite element
    AL> simulations and would like to sample integration point results
    AL> to nodes. To do this I'm using two separate unstructured grid
    AL> files: one with the integration points and their associated
    AL> data, and the other with just the nodes (i.e. points) and
    AL> elements (i.e. cells). I'm working in python (which I'm pretty

I'm not completely clear on what exactly you want to do, but are you
simply trying to convert your PointData to CellData?  If so, you dont
need to go through all this probing.  Simply use the
vtkPointDataToCellData class to do the job.

If that is not the case I am confused with a few things in your data:

 1. brick_8.ipr defines no volumes and only points.  Probing with this
 will only give you the values at these points.  Visualizing these
 points will not be any fun, you'll just see a bunch of tiny coloured
 points.  If you want to probe the volume then you need to probe with
 another volume.

 2. The points in your brick_8.ipr do not coincide with the points in
 brick_8.vtk.  Is this what you want?

 3. I am not entirely sure if probing will work the way you want with
 cell data and point data.

cheers,
prabhu