Straight Construction Line Based on 2D Projection

1. Call the Line command.

2. Select a 2D projection using the following automenu option:

If the option is activated via keyboard, then the projection nearest to cursor gets selected instantly.
If the option is activated via mouse, then you have to additionally press within drawing window for selecting the nearest projection.

Selecting a projection is the optional step, which can be skipped.

3. Using object snappings, move the cursor over a straight graphic line and press or <Enter>. In result, a construction line coinciding with the selected graphic line will be created. If a projection was selected on the previous step, then you can only select graphic lines belonging to such projection. If a projection was not selected, then you can select graphic lines belonging to any projection.

After creating a line the command stays in the mode of creating lines based on the same 2D projection.