A distance or angle can look clear at one zoom level and become hard to read at another. And when atoms move during editing or minimization, a measurement copied from an earlier view may no longer describe the structure on screen. In SAMSON, the Measure editor helps with both problems: it lets you measure geometry directly in the viewport, then save measurements as labels that remain associated with the atoms.
Measure the geometry you need
Open the Measure editor from the left-side viewport menu, or use Ctrl+M on Windows/Linux or Cmd+M on macOS. Then click the relevant feature or atoms:
- Click a bond to show its length.
- Click two atoms to measure the distance between them.
- Click three atoms to measure the angle.
- Click four atoms to measure the torsion.
This gives you a quick way to check a local geometric detail without having to estimate it from the visual arrangement. For example, when comparing two nearby atoms, the displayed distance gives you a direct value; selecting three or four atoms lets you inspect a bend or rotation through the relevant atoms.
Keep the annotation—or let it go
By default, a measurement is temporary. It stays visible regardless of zoom, but disappears when you make another measurement. That is useful for quick checks, but it can be frustrating if you need to keep several measurements visible while reviewing a structure.
To keep one, press Enter after measuring. SAMSON saves it in the document as a label. Repeat this for each measurement you want to retain. If you save the document in a SAMSON format—.sam or .samx—the measurement labels are saved with it. This makes the annotations part of the working document rather than notes that exist only in the current view.
Follow geometry as atoms move
A saved measurement is associated with its atoms, so it can stay useful while you edit the structure. Measurements update automatically in the Viewport, Document view, and Inspector when associated atoms change position. This is handy when using Move editors or interactive minimization: instead of remeasuring after every adjustment, you can watch the value change as the geometry changes.
If you select a saved measurement label and open the Inspector, you can access the atoms associated with it. For a saved atom-to-atom distance, the Inspector also shows additional measurements for projections on planes—useful when you need more than the straight-line distance to understand the relationship between atoms.
Make saved measurements easier to read
Saved measurement labels behave like other labels: their visibility can depend on zoom, and their font, color, and offset can be adjusted. The Inspector also lets you change the colors of distance lines, angle planes, and other measurement elements. If a color change is no longer useful, you can reset line or angle colors by double-clicking the associated text in the Inspector; use the clear button beside Text color to reset the text color.
For consistency across a document, check Preferences > Rendering > Labels. There you can set the font for labels without an individually specified font and choose how many decimal places are displayed for distances and angles created with the Measure editor. Choosing a sensible precision can make annotations easier to scan without implying more certainty than the displayed number provides.
The practical distinction is simple: use a temporary measurement for a one-off check, and press Enter when the value or geometry needs to remain visible, update with the atoms, or travel with the saved document. For more details, see the SAMSON Measuring documentation.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Get SAMSON.