[Paraview] How to calculate offsets in <AppendedData>

[David Ingram]

Dear All,

I've been trying to write out XML formatted data files from a Fortran  
flow solver for use in Paraview,  I have now reached the point where  
the file can be read, provided only one variable is contained in the  
appended data (written in the raw format) and the offset is 0.  I  
have tried calculating offsets based on
1) distance into the 1D array, counting in bytes
2) distance into the 1D array, counting in 4 byte words
neither seems to work.

I've looked at .vti files saved by Paraview itself and the offsets  
don't seem to make sense (for a 10x3 grid, containing cell data the  
first variable is offset at 0 and the second at 48).  If anyone can  
offer assistance I'd be grateful, the file-formats.pdf just describes  
offset as an offset!

I apologise if this is a naive question, but any help would be much  
appreciated

For you information the XML file is as follows

<VTKFile type="ImageData" version="0.1" byte_order="BigEndian">
<ImageData WholeExtent="0   10    0    3    0    0"
   Origin="0.0000E+00  0.0000E+00  0.0000E+00"
   Spacing="0.5000E+00  0.3333E+00  0.1000E+01">
   <Piece Extent="0   10    0    3    0    0">
    <CellData Scalars="Pressure">
     <DataArray Name="Isolid" type="Int32" format="ascii">
-1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1  0  0  0  0  0  0  0  0 -1 -1 -1 -1  
-1 -1
-1 -1 -1 -1 -1

     </DataArray>
     <DataArray Name="Velocity" type="Float32" format="append"  
offset="0"
      NumberOfComponents="2" />
     <DataArray Name="Pressure" type="Float32" format="append"  
offset="60" />
    </CellData>
   </Piece>
</ImageData>
<AppendedData encoding="raw">
_?????...
</AppendedData>
</VTKFile>

looking at the Appended data using bin2hex shows (8 byte groups)

00704: 22 72 61 77 22 3e 0a 5f  3f 80 00 00 00 00 00 00     
"raw">._ ?.......
00720: 3f 80 00 00 00 00 00 00  3f 80 00 00 00 00 00  
00    ?....... ?.......
00736: 3f 80 00 00 00 00 00 00  3f 80 00 00 00 00 00  
00    ?....... ?.......
00752: 3f 80 00 00 00 00 00 00  3f 80 00 00 00 00 00  
00    ?....... ?.......
00768: 3f 80 00 00 00 00 00 00  3f 80 00 00 00 00 00  
00    ?....... ?.......
00784: 3f 80 00 00 00 00 00 00  3f 80 00 00 00 00 00  
00    ?....... ?.......
00800: 3f 80 00 00 00 00 00 00  3f 80 00 00 00 00 00  
00    ?....... ?.......
00816: 3f 80 00 00 00 00 00 00  3f 80 00 00 00 00 00  
00    ?....... ?.......
00832: 3f 80 00 00 00 00 00 00  3f 80 00 00 00 00 00  
00    ?....... ?.......
00848: 3f 80 00 00 00 00 00 00  3f 80 00 00 00 00 00  
00    ?....... ?.......
00864: 3f 80 00 00 00 00 00 00  3f 80 00 00 00 00 00  
00    ?....... ?.......
00880: 3f 80 00 00 00 00 00 00  3f 80 00 00 00 00 00  
00    ?....... ?.......
00896: 3f 80 00 00 00 00 00 00  3f 80 00 00 00 00 00  
00    ?....... ?.......
00912: 3f 80 00 00 00 00 00 00  3f 80 00 00 00 00 00  
00    ?....... ?.......
00928: 3f 80 00 00 00 00 00 00  3f 80 00 00 00 00 00  
00    ?....... ?.......
00944: 3f 80 00 00 00 00 00 00  3f 80 00 00 3f 80 00  
00    ?....... ?...?...
00960: 3f 80 00 00 3f 80 00 00  3f 80 00 00 3f 80 00  
00    ?...?... ?...?...
00976: 3f 80 00 00 3f 80 00 00  3f 80 00 00 3f 80 00  
00    ?...?... ?...?...
00992: 3f 80 00 00 3f 80 00 00  3f 80 00 00 3f 80 00  
00    ?...?... ?...?...
01008: 3f 80 00 00 3f 80 00 00  3f 80 00 00 3f 80 00  
00    ?...?... ?...?...
01024: 3f 80 00 00 3f 80 00 00  3f 80 00 00 3f 80 00  
00    ?...?... ?...?...
01040: 3f 80 00 00 3f 80 00 00  3f 80 00 00 3f 80 00  
00    ?...?... ?...?...
01056: 3f 80 00 00 3f 80 00 00  3f 80 00 00 3f 80 00  
00    ?...?... ?...?...

In this case the 2D velocity vector is (1.0, 0.0) and the pressure is  
1.0, the data is big endian.

Thanks in advance

David

Dr David M Ingram
Reader
Institute of Energy Systems
School of Engineering and Electronics
The University of Edinburgh
Kings Buildings
Mayfield Road
Edinburgh

David.Ingram at ed.ac.uk