A molecular structure can be in the right place visually and still be awkward to position reproducibly. A freehand drag may shift it by an uncertain amount, and a rotation can be hard to repeat if you are not clear about which axes you are using. That becomes especially frustrating when arranging multiple structures or making a sequence of small adjustments.
SAMSON’s move editors help make those operations more controlled. The key is to choose the editor that matches your reference frame, then use snapping or precise parameters when you need repeatable movements.
Choose the reference frame first
Use the Global Move Editor when movements should follow the global X, Y, and Z axes. Its straight-arrow widgets translate along those axes, while its curved-arrow widgets rotate around them. The editor is available with the K shortcut.
Use the Local Move Editor when it is more useful to move or rotate along the selected object’s principal axes. This can be a more natural frame for adjusting a molecule according to its own orientation. Press M to activate it. In either editor, the central translation widget moves the selection in the camera plane, and the trackball allows free rotation.
The Displacer, shortcut D, is a simpler choice when you just need to drag nodes in the camera plane. It is useful for a quick interactive adjustment, but for axis-based movement or controlled rotation, choose the local or global editor instead.
A repeatable positioning workflow
- Select the nodes you intend to move. Move editors act on the selection. If you click and drag a different node with the Displacer, what gets selected depends on the current selection filter.
- Activate the appropriate editor. Choose local axes for movement relative to the selection, or global axes for alignment with the scene’s XYZ frame.
- Use a specific widget. Drag a straight arrow for movement along an axis, a plane widget for movement within a plane, or a curved arrow for rotation around an axis. The widget colors help identify the axes: local axes use shades of blue; global X, Y, and Z are red, green, and blue.
- Turn on snapping when increments matter. Translational and rotational snapping can be adjusted from the editor’s quick-access menu in the viewport or under Interface > Preferences > Editors > Snapping. For example, the documentation demonstrates translation in 0.5 Å increments and rotation in 10° increments. These are examples, not required settings.
- Preview before committing. While dragging, SAMSON displays the movement. Press Esc to cancel and restore the previous position, or release the mouse button to apply the change. Applied moves can also be undone with Edit > Undo.
When the rotation center matters
Rotating a structure around an appropriate point can make the difference between a useful placement and an unexpected sweep through the viewport. For arrangements that involve copies around a central structure, the documentation’s example uses the Global Move Editor with a specified pivot atom and rotational snapping. This combines a deliberate rotation center with consistent angular steps, rather than relying on an imprecise freehand turn.
You can also use context-menu commands when you need to align a structure to the global reference frame rather than manipulate it by eye. Right-click a structure or the current selection and choose Move selection to center it on the origin, align it with an axis, or align it with a plane. For arranging several structures, the Edit > Align and Edit > Distribute commands provide another route.
A simple rule of thumb: use the camera plane for quick screen-space placement, local axes for movement tied to a molecule’s orientation, and global axes when the whole scene is your reference. Add snapping when you need consistent increments, and remember that a drag can be canceled before it is applied.
For editor details and additional examples, see the SAMSON guide to moving objects.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Get SAMSON.