Brief Ruler Explaination:

Red: Vanishing points. You can click and drag them

 

Green: Edits both vanishing points at the same time

 

Blue: Edits singular vanishing point arm

 

Pink: Deactivates vanishing point by clicking on it. Click again to activate

 

Purple: Rotates the orientation of the horizon

 

Yellow: Moves ruler according to the horizon

 

Black circle: Moves ruler without editing it

 

Create a new raster layer, go to Layer>Ruler-Frame>Create Perspective ruler. Choose the perspective according to your needs. In this case I chose a 3 Points perspective.

 

 

I'm going to set my perspective ruler according to the generic vanishing points I drew in my thumbnail. Of course I'm going to adjust it to make the final perspective as stable as possible.

 

When the ruler is active, go to Object>Tool Property and select XZ plane to enable grid.

 

This is how I set my ruler for this composition:

This is how the ruler looks like applied to the thumbnail: