This is a good approach. In recent nightly Slicer versions this process is streamlined:
- Drag-and-drop STL file to Slicer window and in Add data dialog, choose “Segmentation” in Description column (there is no need to load as model and then import to segmentation but you can directly load as segmentation)
- Go to Segment Editor, click “Specify geometry” button (next to Master volume selector)
- Choose current segmentation node as source geometry, set spacing values, click OK
This automatically creates a blank master volume with the necessary size and chosen resolution so that you can edit the segmentation right away.