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Roads have lanes, shelves have rails, circuit boards have traces, and none of them fit in a rectangle. The Line tool draws multi-point polylines that follow any linear structure through the image, however it bends or recedes into perspective.
Available in image projects. A line is a polyline: two clicks make a straight segment, more clicks trace a path. Lines share classes, hotkeys and the instance list with every other annotation type.

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Draw a line

PixlHub editor with the Shelf Edge class and Line tool highlighted, showing a long supermarket shelf

Supermarket example: the Shelf Edge class armed, the Line tool picked, and the finish rule worth memorizing.

1

Arm the class

Press the class hotkey (Shelf Edge is 3 in this project) or click the class name.
2

Pick the Line tool

Click the line icon in the floating palette.
3

Click along the structure

Each click drops a vertex; a dashed preview follows your cursor between clicks. Trace the edge with as many vertices as its curvature needs.
4

Press Enter to finish

Enter completes the polyline. This is the detail everyone misses on day one: lines are open shapes, so there is no first vertex to double-click back to.
The full sequence on a real shelf edge, three vertices and an Enter:
Orange Shelf Edge polyline drawn along a supermarket shelf rail in PixlHub

The finished polyline hugs the shelf rail through perspective; the class chip and instance entry appear like any other annotation.

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Edit a line

Select the line with the Select tool and its vertices become draggable handles, exactly like polygon vertices. Drag to refine the path, press a different hotkey to reclassify, Delete to remove. Undo steps back through individual vertex operations.

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Technique notes

  • Vertices where the direction changes. A straight rail needs two; a curving lane needs one per bend. Extra vertices on straight runs add noise, not precision.
  • Perspective is normal. Structures that recede (like this shelf) are the tool’s home ground; place vertices at consistent visual landmarks such as shelf-lip corners.
  • Zoom for the endpoints. Where a line starts and stops is usually a guideline decision; zoom in at both ends so the cutoff is deliberate.

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Frequently asked questions

If the model needs the centerline or trajectory, use a line. If it needs the painted area itself (for segmentation), outline it with a polygon.
No, Enter seals the shape. Draw a second line and keep them under the same class, or delete and redraw if it must be one continuous path.
As ordered vertex lists with class and metadata, so downstream code can treat them as polylines or sample them into points. Details in Exports.

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Next steps

Polygon tool

Closed outlines for regions instead of paths.

Freeform tool

Continuous freehand drawing when clicking vertices is too slow.