Answers

6.4 Seeing other robots

Seeing more · Robot club · about 15 min

What this lesson is about

Tags from 100 up say who and how far; LEDs say what.

• Why colour and not a tag
• Finding one
• Distance and bearing
• Telling them apart
• Talking with light

Questions 7 marks in all

1. [1 mark]The camera reads a tag with id 101. What is it?

   1. AA marker on the mat
   2. BAnother robot
   3. CA blob
   4. DA misread, because ids stop at 99
   Answer: A. Every tag is a marker on the mat. A robot wears none, so a tag reading is never another robot.

2. [1 mark]What does this program print?

   seen = [['green', 60, 120, 55.0], ['red', 240, 110, 42.0]]
   for colour, cx, cy, dist in seen:
       print(colour, dist, round((cx - 160) * 120 / 320, 1))

   Answer:

   green 55.0 -37.5
   red 42.0 30.0

   The green one is 100 pixels left, -37.5 degrees. The red one is 80 pixels right, 30 degrees.

3. [1 mark]What does robots() give?

   1. AOnly the robots in view, each as [colour, cx, cy, distance]
   2. BEvery robot in the arena, seen or not
   3. CThe ids of the robots, as plain numbers
   4. DThe tags on the robots
   Answer: A. It reads the lit dome on each one, so a robot with its LED off is not in the list.

4. [1 mark]Which of these are true?

   Tick every answer that is true.

   1. AA robot's dome colour says which robot it is
   2. BIts dome can also say what it is doing
   3. CA robot with its LED off is not in robots()
   4. DDomes are best told apart by shade, like light and dark green
   Answer: A, B, C. A lit dome washes out towards white in a camera, so tell robots apart by colour, not shade. About four colours is the limit.

5. [1 mark]A robot's dome is at cx = 272. What is its bearing in degrees?

   Answer: 42 (accept within 0.5). 272 minus 160 is 112 pixels, and 112 times 0.375 is 42 degrees to the right.

6. [1 mark]Your robot runs led("red"). What can the other robots see?

   1. AA red blob, if they look for red with the blob detector
   2. BA tag with a new id
   3. CNothing, the LED is only for people
   4. DA red line
   Answer: A. Light works both ways. A team could agree on what each colour means.

7. [1 mark]What does this program print?

   seen = [['green', 90, 120, 30.0], ['red', 200, 115, 42.0], ['blue', 20, 110, 80.0]]
   near = [r[0] for r in seen if r[3] < 50]
   print("near:", near)
   print("nearest:", seen[0][0])

   Answer:

   near: ['green', 'red']
   nearest: green

   robots() comes back nearest first, so the first one is the closest without any sorting of your own.

The task: spot the robot

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

# every robot in view, nearest first
print(robots())

from bugbot import *
connect()
seen = robots()[0]
bearing = (seen[1] - 160) * 120 / 320
print(f'robot at {seen[3]} cm, bearing {round(bearing, 1)}')
print('dome:', seen[0])