Obstacle avoidance in Unity - Step-by-Step Execution

Concept Flow - Obstacle avoidance

Start

↓

Sense obstacles

↓

Is obstacle close?

No→Move forward

Yes↓

Calculate avoidance direction

↓

Change movement direction

↓

Move

↓

Repeat

The agent senses obstacles, decides if it needs to avoid, calculates a new direction, and moves accordingly.

Execution Sample

Unity

void Update() {
  if (Physics.Raycast(transform.position, transform.forward, out RaycastHit hit, 5f)) {
    Vector3 avoidDir = Vector3.Reflect(transform.forward, hit.normal);
    transform.rotation = Quaternion.LookRotation(avoidDir);
  }
  transform.Translate(Vector3.forward * speed * Time.deltaTime);
}

This code checks for obstacles ahead and changes direction to avoid them while moving forward.

Execution Table

Step	Raycast Hit	Obstacle Distance	Condition (hit < 5)	Action	Movement Direction
1	No	-	False	Move forward	Forward
2	Yes	3	True	Calculate avoidDir, rotate	Avoidance direction
3	No	-	False	Move forward	Forward
4	Yes	4	True	Calculate avoidDir, rotate	Avoidance direction
5	No	-	False	Move forward	Forward
Exit	-	-	No more updates	Stop or continue loop	-

💡 Loop continues each frame; stops when game ends or object destroyed.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
transform.position	(0,0,0)	(0,0,0.1)	(0,0,0.1)	(0,0,0.2)	(0,0,0.2)	Updated each frame
transform.forward	(0,0,1)	(0,0,1)	Reflected vector	Reflected vector	Reflected vector	Changes on avoidance
hit.distance	-	-	3	-	4	-
avoidDir	-	-	(calculated)	-	(calculated)	-

Key Moments - 3 Insights

Why does the object sometimes not avoid obstacles even when close?

Because the raycast might not hit if the obstacle is outside the ray's range or angle, as shown in steps 1 and 3 where no hit occurs.

Why do we use Vector3.Reflect for avoidance direction?

Vector3.Reflect bounces the forward direction off the obstacle's surface normal, giving a smooth avoidance direction (see step 2 and 4 actions).

Why is movement done after rotation?

Rotation changes the facing direction first, so movement forward goes in the new direction, ensuring the object avoids the obstacle effectively.

Visual Quiz - 3 Questions

Look at the execution table, what is the movement direction at step 2?

A Forward

B Backward

C Avoidance direction

D No movement

💡 Hint

Check the 'Movement Direction' column at step 2 in the execution table.

At which step does the raycast detect an obstacle at distance 4?

A Step 3

B Step 4

C Step 1

D Step 5

💡 Hint

Look at the 'Obstacle Distance' column in the execution table.

If the raycast range is increased from 5 to 10, how would the execution table change?

A More steps with 'Yes' raycast hit and avoidance actions

B Fewer avoidance actions

C No change in raycast hits

D Movement direction becomes backward

💡 Hint

Increasing raycast range means detecting obstacles earlier, so more 'Yes' hits in the table.

Concept Snapshot

Obstacle avoidance in Unity:
- Use Physics.Raycast forward to detect obstacles
- If hit within range, calculate avoidance direction with Vector3.Reflect
- Rotate object toward avoidance direction
- Move forward each frame
- Repeat to keep avoiding obstacles dynamically

Full Transcript

In obstacle avoidance, the object uses a raycast to sense obstacles ahead. If an obstacle is detected within a certain distance, it calculates a new direction by reflecting its forward vector off the obstacle's surface. Then it rotates to face this new direction and moves forward. If no obstacle is detected, it continues moving forward. This process repeats every frame to keep the object moving safely around obstacles.