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    <p>Thanks Jacob and all for your input!</p>
    <p>Definitely VDS looks like the way to do it.</p>
    <p>Cheers,</p>
    <p>Zibi<br>
    </p>
    <div class="moz-cite-prefix">On 1/7/19 3:25 PM,
      <a class="moz-txt-link-abbreviated" href="mailto:Jacob.Filik@Diamond.ac.uk">Jacob.Filik@Diamond.ac.uk</a> wrote:<br>
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      cite="mid:71d792f3ab5648daad198434b45576db@Diamond.ac.uk">
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        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Hi
            Zbigniew,<o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">I
            think the only way you could do this would be to use the
            virtual dataset (VDS) feature of HDF5, only available in the
            1.10 release. This should allow you to create a “virtual”
            stack from 4 separate images.<o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">I
            don’t this is a backwardly compatible feature though, so the
            file may not be readable by applications using a pre-1.10
            library version.<o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Kind
            regards,<o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US">Jacob<o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1F497D">Dr
            Jacob Filik</span><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1F497D;background:white">Senior
            Software Scientist</span><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1F497D">Tel:
            +441235 77 8690</span><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"> <o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1F497D">Diamond
            Light Source Ltd.</span><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1F497D">Diamond
            House</span><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1F497D">Harwell
            Science & Innovation Campus</span><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1F497D">Didcot</span><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1F497D">Oxfordshire</span><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Verdana",sans-serif;color:#1F497D">OX11
            0DE</span><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p></o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
        <p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
        <div>
          <div style="border:none;border-top:solid #E1E1E1
            1.0pt;padding:3.0pt 0cm 0cm 0cm">
            <p class="MsoNormal"><b><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext"
                  lang="EN-US">From:</span></b><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext"
                lang="EN-US"> NeXus
                <a class="moz-txt-link-rfc2396E" href="mailto:nexus-bounces@shadow.nd.rl.ac.uk"><nexus-bounces@shadow.nd.rl.ac.uk></a>
                <b>On Behalf Of </b>Zbigniew Reszela<br>
                <b>Sent:</b> 07 January 2019 14:20<br>
                <b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:nexus@nexusformat.org">nexus@nexusformat.org</a><br>
                <b>Subject:</b> [Nexus] HDF5 External Links in NeXus
                files<o:p></o:p></span></p>
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        <p class="MsoNormal"><o:p> </o:p></p>
        <div>
          <p class="MsoNormal"><span
              style="font-size:9.0pt;font-family:"-moz-fixed",serif">Hi
              NeXus experts,<br>
              <br>
              I'm not sure if your list is for this kind of questions.
              If not, could you please advice where to look for help and
              forgive me this message.<br>
              <br>
              We would like to write a HDF5 file, let's call it the
              master file, with multiple NXScan entries. The scan can be
              configured so the detector's data are directly stored in
              the master file or the detector's data are stored in a
              separate file(s), let's call it the slave file(s). In the
              later case, in the master file, we would like to use the
              HDF5 external links to the slave file(s). The idea is to
              provide as transparent as possible (between these two
              saving modalities) access to the data.<br>
              <br>
              Let me illustrate it with an example. A scan involves just
              one detector and provides 4 frames each of 1024x1024
              shape.<br>
              If the scan is configured to store the data in the master
              file, this can be accessed in the following way:<br>
              <br>
              In [6]: f["entry1"]["measurement"]["twod01"]<br>
              Out[6]: <HDF5 dataset "twod01": shape (4, 1024, 1024),
              type "<f8"><br>
              <br>
              If the scan is configured to store the detector's data in
              the slave file (all 4 frames in one dataset) and we use
              the following code to insert the external link:<br>
              <br>
              f = h5py.File("master.h5")<br>
              f["entry1"]["measurement"]["twod01"] =
              h5py.ExternalLink("slave.h5", "/data")<br>
              <br>
              then we can access the data from the master file:<br>
              <br>
              In [24]: f["entry1"]["measurement"]["twod01"]<br>
              Out[24]: <HDF5 dataset "data": shape (4, 1024, 1024),
              type "<u4"><br>
              <br>
              My question is how to create the external links (or use
              some alternative solution) if the detector's data are
              stored in multiple files, for example 1 frame per file (4
              slave files in total), or 2 frame per file (2 slave files
              in total). Here we would like to maintain the way of
              accessing all the scan frames with the
              f["entry1"]["measurement"]["twod01"] syntax.<br>
              <br>
              Thanks in advance for sharing your experience,<br>
              <br>
              Zbigniew Reszela<br>
              (Alba Synchrotron) <o:p></o:p></span></p>
        </div>
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          <p class="MsoNormal"><o:p> </o:p></p>
          <div>
            <div>
              <p class="MsoNormal"><o:p> </o:p></p>
            </div>
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      <p align="justify"> </p>
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