data
virtual datasetimage_key not register in tomo_v2_external
some unit missing
counter is saved as a detector. Why ? -> how to know which node contains 'camera' and which don't ?
-> have to filter the 'detector name'
rotation is sometime named srot, sometime hrsrot !!! (and for projection both are recorded !!!!) So in this case the order of checking key matter !!!
for reference: several frame, one srot value !!!