The HDF_VG_ISVD function returns true if the object associated with Id is a VData in a Hierarchical Data Format file.
Result = HDF_VG_ISVD( VGroup, Id )
The VGroup handle returned by a previous call to HDF_VG_ATTACH.
The VGroup or VData reference number obtained by a previous call to HDF_VG_GETNEXT.
Vid = HDF_VG_GETNEXT(Vgrp, -1)
PRINT, HDF_VG_ISVD(VGrp, Vid)