It does not seem to matter if free snap is on or off, Restrict Orthangonal forces you to start a line from somewhere on the x or y plane of the Relative Zero Point. This behavior is shared with (inherirted from?) Qcad, and departs from the Autocad convention. I know the way its been done for 40 years is not always right, but in this case the fixation on relative zero is limiting.
Try starting the line with Restrict Vertical/Horizontal turned off, then turn it on to finish the line. That's how I've been using it, anyway.
Another solution is to not use Restrict Vertical/Horizontal but hold down the shift key after starting a line. This constrains the line to 15° angle intervals so if you hold the cursor close to horizontal or vertical, you can place the endpoint vertically or horizontally from the start point.
- press SHIFT to set the second point, this enables 15° snap and gives exact horizontal/vertical lines too
- use the command line, set first point, then enter @100,0 - that sets the endpoint 100 to the right horizontally (because Y=0)
- or enter @100<90 - 90 is the angle and creates a vertical line
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Thanks for asking this question and thanks for those who answered. This was my question too. I wanted to make a series of straight lines with the Restrict Vertical / Restrict Horizontal turned on and it locked the cursor to wherever the Relative Zero position was. My confusion came because I followed a LibreCAD tutorial where the instructor used the Restrict Horizontal / Vertical often and I thought he was telling us to turn it on and draw lines but he might have been setting the start point of the line then turning on the Restrict when he was going to set the second point. I will probably be using the Shift Key method too as long as I can remember it.