> For the complete documentation index, see [llms.txt](https://docs.imerit.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.imerit.net/labeling/labeling-editor-interface/medical-labeling-editor/line-tape-measure.md).
# Line (Tape Measure)
The Polyline tool allows you to create open 3D lines with two or more points in medical assets. A line can span multiple slices and views, and its measurement is the total length of all its segments.
## Creating a Line
In the medical labeling editor, click on a "Polyline"-type class from the "Tools" section on the left.
Click with the left mouse button on the volume to place the first point, then click to add more points. You may scroll to another slice or move to another view before placing the next point. Each point stays on the slice where you placed it. You can also draw in an oblique view while using [Reformat](/labeling/labeling-editor-interface/medical-labeling-editor.md#reformat).
Once you have placed at least two points, press **N** or click the last point again to finish the line. The line remains open: its last point is not joined to its first point.
{% hint style="info" %}
Placing the second point does not finish the line. Even for a two-point measurement, press **N** or click the last point again to finish.
{% endhint %}
While drawing, right-click to remove the last point, or press **Esc** to cancel the line.
A completed three-point line, measured in millimeters.
## Viewing a Line Across Slices
Segments that lie on the current slice appear as solid lines. Where a segment crosses the slice between two points, an **x** marker indicates the crossing. Hover over this marker to see the point numbers and their distances from the current slice.
When you hover over or select a line, a faint dashed outline shows the parts on other slices. The complete line is also visible in the [3D Viewer](/labeling/labeling-editor-interface/medical-labeling-editor.md#3d-viewer).
In the 3D view, polylines remain visible through segmentations as faded lines.
## Editing a Line
With no labeling tool active, select the line to edit it.
These editing controls apply to hand-drawn lines. Lines created with [Extract Centerline](/labeling/labeling-editor-interface/medical-labeling-editor/extract-centerline.md) are read-only; you can select and delete them, but cannot edit their points or move them.
* **Move a point:** click and drag the point. In axial, coronal, and sagittal views, it stays on its original slice.
* **Delete a point:** right-click the point. A line must keep at least two points.
* **Insert a point:** hold **Ctrl** and click a segment or an **x** crossing marker.
* **Extend a line:** hold **Shift** and click its first or last point, then click to add points. Press **N** or click the last point again to finish.
* **Move the whole line:** click and drag the line itself.
### Viewing the Line Measurement
As you hover over the line, or click on it, its total real-world length in millimeters will become visible. The measurement adds together the lengths of all segments and updates while you drag a point:
The Objects panel also shows the measurement next to each line. When multiple lines use the same class, the class header shows their total measurement. If the lines use different units, Ango Hub displays a separate total for each unit.
Measurements and totals update when you move, edit, or delete a line.
## Changing the Class of a Line
Left click on the line to select it, then right-click anywhere on the line and click on the three dots.
Then, from the "Change Category" sub-menu, pick the class you'd like to change the line to. The line will be assigned to that class.
## Adding a Description / Name to a Line
You may add a manual text description or name to a line by clicking on it and pressing "D" on your keyboard.
## Quickly Navigating to a Line
You may quickly navigate to the slice where a line was drawn by holding Ctrl and hovering with the mouse cursor over the line's row in the "Objects" panel on the left-hand side of the screen.
---
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