Hi Hom Nath,
Thank you very much for your email. The code you send it starting to make sense
for me, I would just appreciate if you would explain a few things for me. At
the minute I am outputting as follows within <AppendedData>:
size = idim*jdim*sizeof(float);
totalsize = size*4;
file << "_";
file.write(reinterpret_case<const char*>(&totalsize), 4);
file.write(&Array1, size);
file.write(&Array2, size);
file.write(&Array3, size);
file.write(&Array4, size);
But sadly it's not working. I compute the offset as:
for (i = 0; i < 4; i++)
{
offset[i] = i*size;
}
Things get extremely strange in Paraview. I have one outputting five arrays
same as above and I can read and view for first, third and fifth no problems
but not the second or the fourth. The three that read even look like they
should (although without extremely detailed checking.
I assume I am missing something about how to either compute the offset or the
binary layout. Your code seems to say that each dataarray should have its own
integer binary output tells the size of that data instead of just one at the
start of the array?
Any help is greatly appreciated.
David
From: Hom Nath Gharti
Sent: Wednesday, April 01, 2009 1:59 PM
To: David Mulholland
Cc: Thorsten Hater ; [email protected]
Subject: Re: [Paraview] VTK XML Binary Output
I thought my C code may be helpful to you. I have 5 data array of different
size, and I do like this:
nvar=5;
/* Bytes and offsets for ParaView file */
bytes[0] = (ndim*nnod)*sizeof(float); /* Coordinates */
bytes[1] = (nenod*nelmt)*sizeof(int); /* Connectivity */
bytes[2] = (nelmt)*sizeof(int); /* Offsets */
bytes[3] = (nelmt)*sizeof(int); /* Types */
bytes[4] = (nelmt)*sizeof(float); /* Cell data */
off[0]=0; /* 1st offset */
for (i=0; i<nvar; i++){
if(i<nvar-1)off[i+1]=off[i]+sizeof(int)+bytes[i];
bytes[i]=bytes[i]+sizeof(int); /* For each byte we must also add the
sizeof(int) for itself also */
}
Best wishes,
Hom Nath
2009/4/1 David Mulholland <[email protected]>
Hi Thorsten,
I just tried that and it is now giving me a segmentation fault... I am using
the following line:
file.write(reinterpret_cast<const char*>(size), 4);
My size is calculated as - int size = idim*jdim*sizeof(float). idim is
currently in the region of 400 and jdim 200. I am outputting big files and it
is likely to get bigger.
Also, I intend to include more data arrays each timestep, I just want to get
it working with pressure first and then I will include then which is why I want
to calculate the offset... I assuming it is just the number of bytes to the
start of the next datafield...
Thanks David
From: Thorsten Hater
Sent: Wednesday, April 01, 2009 10:55 AM
To: David Mulholland
Cc: [email protected]
Subject: Re: [Paraview] VTK XML Binary Output
Hello David,
the offset parameter is relevant if you append mulitple data sections into a
single file.
Every DataArray tag with append format specifies the offset as the position
in the
binary data in bytes.
To write the integer I use the following:
std::ofstream os; // binary mode (for windows ...) ofstream to your file
int N; // size in bytes
os.write(reinterpret_cast<const char*>(N), 4);
Thorsten
David Mulholland schrieb:
Hi Thorsten,
That's really helpful. I don't quite know how to write out the number of
bits as a char? If you could explain a way of how to do that it would be
greatly appreciated.
Also, how do I calculate what value goes in for the offset? I had a look at
a couple of output files from paraview and it wasnt obvious how it was
calculated.
Thanks
David
From: Thorsten Hater
Sent: Tuesday, March 31, 2009 2:23 PM
To: David Mulholland
Cc: [email protected]
Subject: Re: [Paraview] VTK XML Binary Output
Hello,
the solution might be to append your data as
< DataArray ... format="appended">
</DataArray>
< AppendedData encoding="raw">
_NNNNData
</AppendedData>
where you should replace NNNN with a four
byte integer containing the number of bytes
in the data array as 4 chars.
Setting the encoding to "raw" tells ParaView, that
the data is simply a stream of bytes rather than
base64 encoded.
If you want to write Image I can supply a small
writer project for 2D data.
Thorsten
David Mulholland schrieb:
Hello,
I am currently trying to write my own quick output routine to generate a
binary file using C++. I am currently trying to avoid having to use the
vtk
libraries because I only need a very basic output that doesn't change
much.
I so far have the ASCII output working no problem but I can't get the
binary
working.
I am using file.write() function to output the binary data and that seems
to
be working no problem and when used in a legacy format application it
works
perfectly except that the data is LittleEndian instead of BigEndian.
That's
why I have moved to BigEndian because I don't want to have to make the
output routine for the data anymore complicated that file.write.
I started using the xml format and considering my output is raw binary
and
not base64 I changed it to be in the AppendedData section instead of
DataArray. It still isn't working right, I get the following error when I
try to load in ParaView:
ERROR: In ..\..\..\ParaView3\VTK\IO\vtkXMLStructuredDataReader.cxx, line
349
vtkXMLImageDataReader (0ADEC7F8): Error reading extent 0 422 0 242 0 1
from
piece 0
ERROR: In ..\..\..\ParaView3\VTK\IO\vtkXMLDataReader.cxx, line 537
vtkXMLImageDataReader (0ADEC7F8): Cannot read cell data array "pressure"
from PointData in piece 0. The data array in the element may be too
short.
The format of my output file is as follows:
<?xml version="1.0"?>
<VTKFile type="ImageData" version="0.1" byte_order="LittleEndian">
<ImageData WholeExtent="0 422 0 242 0 1" Origin="0 0 0" Spacing="1 1 1">
<Piece Extent="0 422 0 242 0 1">
<PointData>
</PointData>
<CellData Scalars="pressure">
<DataArray type="Float32" Name="pressure" format="appended" offset="0"/>
</CellData>
</Piece>
</ImageData>
<AppendedData encoding="raw">
_BINARYDATA
</AppendedData>
</VTKFile>
Note following an error message I have added an _ at the start of the
binary
data. Is this required?
One final thing, when using appended data, how do you calculate what the
offset should be?
Thanks
David
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Please keep messages on-topic and check the ParaView Wiki at:
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Follow this link to subscribe/unsubscribe:
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