Tracing feature in Earthlight is a feature which allows you to trace mouse cursor to alongside edges of a specified layer or group of layers. In tracing mode, you will be able to add nodes only alongside existing edges of geometries (unless the 'Allow non-traceable points' option is active in Trace settings) which you trace to.

To start using Trace feature, it is required to set trace layers first.

To do this please open context menu with your right mouse button and select 'Trace settings'.

Please note

Context menu will be available only when you are in editing mode and have a tool from the 'Add New Geometries' group selected.

In the 'Snap/trace to:' dropdown, you can select to which layers cursor should trace to. It is possible to select an built-in group like 'Stencil layers', groups of layers or specific layers from your map.

You can select more than one item and all selected items will be marked with orange colour.

When all tracing settings are properly set, you can start using tracing feature. To start, please open context menu and select the 'Trace: ' option. When snapping is active, bolded 'Trace : On' text will be displayed in context menu.

Now you can hover over the traced geometry edge and add first node by clicking in desired location. Black point will be displayed.

Please note

If any snapping points have been set, your cursor will snap to those. For more information about setting snapping points, please visit the 'Snap' tool description.

Black line connecting start point and current cursor position will be displayed.

After adding the second node, line or polygon will be created, using marked edge. You can continue drawing with the Trace option active or turn off the option and finish polygon or line outside the edge which was traced.

The result:

Additional trace settings:

Snapping/tracing attraction radius (in pixels):
By adjusting this slider, you can choose how close to snapping points, you will have to move your cursor.
Tracing zone radius (in pixels)
When active (set > 0px) creates circle zone around your cursor with specified radius. Tracing trail will be drawn only when the cursor is in it.
Without this option I can quickly move from one point on an edge to another, without actually following the edge.

When the option is active, tracing zone was created and if the cursor will be moved not alongside the edge, tracing trail will not be drawn.

With this option enabled, it is required to move cursor alongside a geometry edge, up to the next desired node location.
Mask opacity:
Using this slider you can control opacity of the tracing mask, when the trace option is active.

You can configure the default Snap/Trace settings in the Global/Inheritable User Settings in Editing tab.

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