Computes the relative offset vector between a Robot and a Location (presumed to be in the same subworld, though the contrary will not result in failure), then re-interpret that vector based on the Robot's current orientation.

If the robot is not oriented in a cardinal direction, returns Nothing.

Re-orientation semantics

Given a displacement vector (x, y) where:

• positive x-coordinate represents east
• negative x-coordinate represents west
• positive y-coordinate represents north
• negative y-coordinate represents south

the re-interpreted vector (x', y') becomes:

• positive x'-coordinate represents right
• negative x'-coordinate represents left
• positive y'-coordinate represents forward
• negative y'-coordinate represents back