DICOM export to correctly identify master volume

[cpinter]

When performing DICOM-RT import, then DICOM-RT export with Eclipse pelvis sample data, no output files are created. Instead, the following error message appears:

Failed to resample segment BODY to match anatomical image geometry

If RTIMAGE objects are removed from the study before export, then export is successful.

(Formerly called: DICOM Export: RTSTRUCT resampled to wrong volume)

Migrated from https://app.assembla.com/spaces/slicerrt/tickets/810-dicom-export-to-correctly-identify-master-volume/details

[cpinter]

The problem is that if the user wants to export a study with multiple volumes in it, then the RT image may be considered the CT (need to check why, and how to prevent that)

Also see if SH multi-selection can be used for DICOM export