[NeXus-tech] Nexus C++ API by DESY

[Mark Koennecke]

Hi,

I order to add my 2c worth:

I looked at the file in hdfview and saw that the type of the attribute 
is 32 bit float.
This is not good for text of any form. Checking in napi5.c reveals that 
string attributes
are stored as HDF-5 type H5T_C_S1.

Best Regards,

                Mark

On 02/22/2012 04:17 PM, Pete Jemian wrote:
> walking through that with hdfview
>
> /scan_1/sample/GLS/soft_limit_max
>    attribute is "units", not "unit" (other places as well)
>    Is a value assigned to this dataset?
>      array length is 1, value is empty
>      should it be a number, not a string?
>
> /scan_1/sample/GLS/soft_limit_min
>    change "unit" attribute to "units"
>    array of length 1, value of 0.0 found
>
> there's more so I switched to using h5toText.py, output attached.
>
> Summary, you are probably correct that you've selected a string 
> representation that conflicts with the NAPI representation of a string.
>
> Here's a snippet from an HDF5 file written by GDA at Diamond Light 
> Source:
>
>   @file_time = 2011-06-02T19:32:44+00:00
>   entry1:NXentry
>     @NX_class = NXentry
>     entry_identifier:char[5] = 31672
>     program_name:char[10] = GDA 8.12.0
>     scan_command:char[14] = static readout
>     scan_dimensions:int32 = 1
>     scan_identifier:char[36] = 67b05b7f-454f-4ed4-8914-f442c710fdeb
>
> Compliant strings seem to be fixed length "array of char".
> This does not address the error you reported below.
>
> Look at /scan_1/instrument/Slit3/center_ver/@unit and 
> /scan_1/instrument/Slit3/center_ver/@description, something got 
> tangled up:
>
>         center_ver:float32 = 0.0
>           @unit = 5.18226e-38
>           @description = 5.19678e-38
>
> This is the same for all four slits (Slit1, Slit2, Slit3, Slit4)
> Might be the problem.  The other attributes look like they have 
> reasonable values.
>
> How come nxconvert or nxdir do not give a more detailed error message?
> Which attribute is the one that triggered the exception and what was 
> the defect?
>
> Pete
>
>
> On 2/22/2012 3:30 AM, Eugen Wintersberger wrote:
>> Hi folks
>>    as you know I am developing a C++ API for Nexus within the HDRI
>> project. Attached to this file you find a first Nexus file written by
>> the API. As far as I see all attributes are set correctly. However,
>> nxconvert or nxdir give the following error
>>
>> ERROR: HDF could not read attribute data
>>
>> I assume that this is due to the fact that I use variable length UTF8
>> strings to store string data. This gives me the possibility to write
>> fields of strings where the strings have variable length.
>> Can someone please have a look on the file to confirm my assumption or
>> maybe finds another reason why nxconvert or nxdir do not work as
>> expected?
>>
>> best regards
>>     Eugen Wintersberger
>>
>>
>>
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>
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