Hello Aart-Jan!
I agree that this is an inefficient and undesireable limitation for TDMS file editing. DIAdem 10.1 shipped with a new function,
DataFileHeaderAccess(), which creates a TDM header object that you can use to read off the hierarchy and property values of all data files for which there is a DataPlugin (without loading the file into DIAdem memory). For TDM files only, this object can also change any of the property values WITHOUT touching the binary file. This is particularly easy for TDM files because they store all the descriptive information (structure plus properties) in a separate XML file with the file extension TDM, while all the bulk (numeric and date/time) data are stored in a separate binary file, usually with the file extension TDX. So it's an easy matter to rewrite the TDM file to change the property values, because it's a small ASCII file completely separate from the huge binary data.
TDMS, though, is built for streaming speed and uses only 1 binary file which is designed to be written to buffer by buffer. Each buffer has a binary header and binary data section. The Data Portal structure and the property values are stored in the same file as the binary data values in one or more of these binary buffers. Since some properties are strings, so that you never know how many bytes they will take up, there's no guaranteed way to replace the string property value in the existing binary file without potentially truncating the property string or overwriting neighboring binary data. Now that you mention it, though, it should be possible with the
DataFileHeaderAccess(), to add a new binary header at the very end of the TDMS file which clobbers the previously declared values of one or more properties, but to my knowledge this is not implemented. I will check with R&D if this is something they can add to their list.
For the time being, you either convert to TDM so that you can make all the property changes you want, or you stick with TDMS and live with the file re-write. I will get back to you on your other thread when I have the exact details of the large TDMS file export error. I believe this is fixed now in a newer version of the TDMS DataPlugin, and I am just checking which older versions of DIAdem it will work with and also how to deliver it to you.
What version of DIAdem do you have?
Brad Turpin
DIAdem Product Support Engineer
National Instruments