Vector3.ProjectOnPlane

Parameters

Returns

Vector3 The orthogonal projection of vector on the plane.

Description

Projects a vector onto a plane.

For a given plane described by planeNormal and a given vector vector, Vector3.ProjectOnPlane generates a new vector orthogonal to planeNormal and parallel to the plane. Note: planeNormal does not need to be normalized.


''The red line represents vector, the yellow line represents planeNormal, and the blue line represents the projection of vector on the plane.''

The script example below makes Update generate a vector position, and a planeNormal normal. The Vector3.ProjectOnPlane static method receives the arguments and returns the Vector3 position.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

// Vector3.ProjectOnPlane - example

// Generate a random plane in xy. Show the position of a random
// vector and a connection to the plane. The example shows nothing
// in the Game view but uses Update(). The script reference example
// uses Gizmos to show the positions and axes in the Scene.

public class Example : MonoBehaviour
{
    private Vector3 vector, planeNormal;
    private Vector3 response;
    private float radians;
    private float degrees;
    private float timer = 12345.0f;

    // Generate the values for all the examples.
    // Change the example every two seconds.
    void Update()
    {
        if (timer > 2.0f)
        {
            // Generate a position inside xy space.
            vector = new Vector3(Random.Range(-1.0f, 1.0f), Random.Range(-1.0f, 1.0f), 0.0f);

            // Compute a normal from the plane through the origin.
            degrees = Random.Range(-45.0f, 45.0f);
            radians = degrees * Mathf.Deg2Rad;
            planeNormal = new Vector3(Mathf.Cos(radians), Mathf.Sin(radians), 0.0f);

            // Obtain the ProjectOnPlane result.
            response = Vector3.ProjectOnPlane(vector, planeNormal);

            // Reset the timer.
            timer = 0.0f;
        }
        timer += Time.deltaTime;
    }

    // Show a Scene view example.
    void OnDrawGizmosSelected()
    {
        // Left/right and up/down axes.
        Gizmos.color = Color.white;
        Gizmos.DrawLine(transform.position - new Vector3(2.25f, 0, 0), transform.position + new Vector3(2.25f, 0, 0));
        Gizmos.DrawLine(transform.position - new Vector3(0, 1.75f, 0), transform.position + new Vector3(0, 1.75f, 0));

        // Display the plane.
        Gizmos.color = Color.green;
        Vector3 angle = new Vector3(-1.75f * Mathf.Sin(radians), 1.75f * Mathf.Cos(radians), 0.0f);
        Gizmos.DrawLine(transform.position - angle, transform.position + angle);

        // Show the projection on the plane as a blue line.
        Gizmos.color = Color.blue;
        Gizmos.DrawLine(Vector3.zero, response);
        Gizmos.DrawSphere(response, 0.05f);

        // Show the vector perpendicular to the plane in yellow
        Gizmos.color = Color.yellow;
        Gizmos.DrawLine(vector, response);

        // Now show the input position.
        Gizmos.color = Color.red;
        Gizmos.DrawSphere(vector, 0.05f);
        Gizmos.DrawLine(Vector3.zero, vector);
    }
}