Range finder for terrain following in Drone Programming - Step-by-Step Execution

Concept Flow - Range finder for terrain following

Start

↓

Read range finder sensor

↓

Calculate altitude error

↓

Adjust drone altitude

↓

Check if mission complete

No Yes↓

Repeat

The drone reads the range finder sensor, calculates altitude error, adjusts altitude, and repeats until the mission is complete.

Execution Sample

Drone Programming

altitude_setpoint = 10
while mission_active:
    current_altitude = read_range_finder()
    error = altitude_setpoint - current_altitude
    adjust_altitude(error)
    if mission_complete():
        break

This code keeps the drone at a set altitude by reading the range finder and adjusting altitude until the mission ends.

Execution Table

Step	Action	current_altitude (m)	error (m)	Altitude Adjustment	Mission Complete?
1	Read sensor	8.5	10 - 8.5 = 1.5	Increase altitude by 1.5	No
2	Read sensor	9.2	10 - 9.2 = 0.8	Increase altitude by 0.8	No
3	Read sensor	9.9	10 - 9.9 = 0.1	Increase altitude by 0.1	No
4	Read sensor	10.0	10 - 10.0 = 0.0	No adjustment	No
5	Read sensor	10.1	10 - 10.1 = -0.1	Decrease altitude by 0.1	No
6	Read sensor	10.0	10 - 10.0 = 0.0	No adjustment	Yes

💡 Mission complete detected at step 6, loop exits.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	After 6
current_altitude	N/A	8.5	9.2	9.9	10.0	10.1	10.0
error	N/A	1.5	0.8	0.1	0.0	-0.1	0.0
mission_active	True	True	True	True	True	True	False

Key Moments - 3 Insights

Why does the error become negative at step 5?

At step 5, current_altitude is 10.1 which is above the setpoint 10, so error = 10 - 10.1 = -0.1, indicating the drone is too high and needs to decrease altitude.

Why is there no altitude adjustment at step 4?

At step 4, error is zero (10 - 10.0 = 0), so the drone is at the desired altitude and no adjustment is needed, as shown in the execution_table row 4.

When does the loop stop running?

The loop stops when mission_complete() returns True, which happens at step 6, causing mission_active to become False and exiting the loop.

Visual Quiz - 3 Questions

Look at the execution table, what is the error value at step 3?

A 1.5

B 0.8

C 0.1

D -0.1

💡 Hint

Check the 'error (m)' column in row 3 of the execution_table.

At which step does the drone first stop increasing altitude?

A Step 2

B Step 4

C Step 5

D Step 6

💡 Hint

Look at the 'Altitude Adjustment' column to find when it says 'No adjustment' for the first time.

If the altitude_setpoint was changed to 12, how would the error at step 1 change?

A It would be 3.5

B It would be -1.5

C It would stay 1.5

D It would be 10

💡 Hint

Calculate error as altitude_setpoint - current_altitude using the new setpoint and step 1 altitude.

Concept Snapshot

Range finder terrain following:
- Read sensor for current altitude
- Calculate error = setpoint - current altitude
- Adjust altitude based on error
- Repeat until mission complete
- Keeps drone flying at desired height over terrain

Full Transcript

This visual execution shows how a drone uses a range finder sensor to maintain a set altitude for terrain following. The drone reads the current altitude, calculates the difference from the desired altitude (error), and adjusts its altitude accordingly. The process repeats until the mission is complete. The execution table traces each step's sensor reading, error calculation, altitude adjustment, and mission status. Key moments clarify why error can be negative, when no adjustment is needed, and when the loop stops. The quiz tests understanding of error values, adjustment timing, and effects of changing the setpoint.

Practice

1.

What is the main purpose of a range finder in drone terrain following?

easy

A. To measure the distance between the drone and the ground

B. To control the drone's speed horizontally

C. To detect obstacles in the air above the drone

D. To measure the drone's battery level

Solution

1. Step 1: Understand the role of a range finder

   A range finder is a sensor that measures how far the drone is from the ground below it.

2. Step 2: Connect measurement to terrain following

   This distance helps the drone adjust its height to follow the shape of the terrain safely.

3. Final Answer:

   To measure the distance between the drone and the ground -> Option A

4. Quick Check:

   Range finder = distance measurement [OK]

Hint: Range finder always measures distance to ground [OK]

Common Mistakes:

• Confusing range finder with speed sensor
• Thinking it measures battery or air obstacles
• Assuming it controls horizontal movement

2.

Which of the following code snippets correctly reads a range finder sensor value in a drone program?

1. distance = range_finder.read()
2. distance = read.range_finder()
3. distance = rangeFinder.readValue()
4. distance = range_finder.get()

easy

A. 2. distance = read.range_finder()

B. 3. distance = rangeFinder.readValue()

C. 1. distance = range_finder.read()

D. 4. distance = range_finder.get()

Solution

1. Step 1: Identify correct method call syntax

   In drone programming, sensors are often objects with a method called read() to get current values.

2. Step 2: Check each option for correct syntax

   Option 1 uses range_finder.read(), which is standard and correct. Others use incorrect method names or syntax.

3. Final Answer:

   1. distance = range_finder.read() -> Option C

4. Quick Check:

   Sensor read method = read() [OK]

Hint: Sensor reading usually uses .read() method [OK]

Common Mistakes:

• Using wrong method names like get() or readValue()
• Incorrect object.method order
• Confusing variable names with method calls

3.

What will be the output of this code snippet controlling drone height?

distance = 5
if distance < 3:
    action = "ascend"
elif distance > 7:
    action = "descend"
else:
    action = "hold"
print(action)

medium

A. "ascend"

B. "hold"

C. "descend"

D. Error

Solution

1. Step 1: Evaluate the distance condition

   The distance is 5. Check if 5 < 3 (false), then if 5 > 7 (false).

2. Step 2: Determine the else branch

   Since both conditions are false, the else branch runs, setting action to "hold".

3. Final Answer:

   "hold" -> Option B

4. Quick Check:

   Distance 5 triggers else = hold [OK]

Hint: Check conditions in order, else runs if none match [OK]

Common Mistakes:

• Choosing ascend or descend incorrectly
• Confusing comparison operators
• Assuming error due to syntax

4.

Find the error in this drone height control code:

distance = range_finder.read()
if distance < 2
    action = "ascend"
else:
    action = "descend"
print(action)

medium

A. range_finder.read() is invalid

B. Wrong comparison operator

C. Incorrect indentation of else

D. Missing colon after if condition

Solution

1. Step 1: Check syntax of if statement

   The if statement is missing a colon (:) at the end of the condition line, which is required in Python-like syntax.

2. Step 2: Verify other parts

   Comparison operator and indentation are correct. The method call is valid assuming range_finder object exists.

3. Final Answer:

   Missing colon after if condition -> Option D

4. Quick Check:

   if statement needs colon : [OK]

Hint: Always put colon after if condition [OK]

Common Mistakes:

• Forgetting colon after if
• Misaligning else indentation
• Changing comparison operators unnecessarily

5.

You want the drone to maintain a height of 4 meters above ground using the range finder. Which code snippet correctly adjusts the drone's vertical speed based on the measured distance?

distance = range_finder.read()
if distance < 4:
    vertical_speed = 1  # ascend
elif distance > 4:
    vertical_speed = -1 # descend
else:
    vertical_speed = 0  # hold steady
print(vertical_speed)

hard

A. This code correctly sets vertical_speed to keep 4m height

B. The conditions should use <= and >= instead of < and >

C. vertical_speed values should be reversed for ascend and descend

D. The else block is unnecessary and should be removed

Solution

1. Step 1: Understand the desired behavior

   The drone should ascend if below 4m, descend if above 4m, and hold if exactly 4m.

2. Step 2: Check code logic

   If distance < 4, vertical_speed = 1 (ascend) is correct. If distance > 4, vertical_speed = -1 (descend) is correct. Else holds steady at 0.

3. Final Answer:

   This code correctly sets vertical_speed to keep 4m height -> Option A

4. Quick Check:

   Conditions match desired height control [OK]

Hint: Ascend if below target, descend if above, else hold [OK]

Common Mistakes:

• Reversing ascend and descend speeds
• Removing else block causing no hold state
• Using <= or >= unnecessarily