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How to make a ground object follow a flying object in unity?

I'm trying to make an object on the ground follow a flying object, for example a drone leading a human (for now i'm just using shapes - a cube and a capsule). My cube follows the capsule like i desire but i want the cube to follow the capsule on the ground only, rather than go up on the y-axis with the capsule. Right now, it follows the capsule everywhere, I want the capsule to lead while the cube follows along on the ground.
I have done some research on Google and Youtube but I have not seen any results. Please let me know how I can achieve this.
This is the code script attached to the cube(ground object)
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
public class follow_target : MonoBehaviour
{
public Transform mTarget;
float mSpeed = 10.0f;
const float EPSILON = 0.1f;
Vector3 mLookDirection;
// Start is called before the first frame update
void Start()
{
}
// Update is called once per frame
void Update()
{
mLookDirection = (mTarget.position - transform.position).normalized;
if((transform.position - mTarget.position).magnitude > EPSILON)
transform.Translate(mLookDirection * Time.deltaTime * mSpeed);
}
}

If the ground is planar, you can just set the y component to 0 (or whatever the ground y vector is).
If the ground changes in topology, you can do a raycast down from the capsule to get the hit point (vector3). You can use the hit point y component for the height. After that you will need to set the cubes rotation so that it is aligned to the ground. You could do that with a raycast as well, there are a number of examples of that online.
I hope that helps get you in the right direction.

Assuming a flat ground on Y = 0
either make sure your objects sticks to the ground so set
private const float EPSILONSQR = EPSILON * EPSILON;
void Update()
{
var difference = mTarget.position - transform.position;
mLookDirection = difference.normalized;
if(difference.sqrmagnitude > EPSILONSQR)
{
// In general be aware that Translate by default moves in the
// objects own local space coordinates so you probably would rather
// want to use Space.World
transform.Translate(mLookDirection * Time.deltaTime * mSpeed, Space.World);
var pos = transform.position;
// reset the Y back to the ground
pos.y = 0;
transform.position = pos;
}
}
or simply already map the direction down on the XZ plane (ignoring any difference in Y) like
private const float EPSILONSQR = EPSILON * EPSILON;
void Update()
{
var difference = mTarget.position - transform.position;
mLookDirection = difference.normalized;
// simply ignore the difference in Y
// up to you if you want to normalize the vector before or after doing that
mLookDirection.y = 0;
if(difference.sqrmagnitude > EPSILONSQR)
{
transform.Translate(mLookDirection * Time.deltaTime * mSpeed, Space.World);
}
}

Unity3D - Why doesn't my player rotate properly?

I'm building a top down shooter and so I have my camera above my player and the map. Here's the code I've written in the player controller script for movement:
public class playerMovement : MonoBehaviour {
public float speed;
private Camera mainCamera;
void Start () {
mainCamera = FindObjectOfType<Camera>();
}
// Update is called once per frame
void Update () {
// player movement
transform.Translate(speed * Input.GetAxis("Horizontal") * Time.deltaTime, 0f, speed * Input.GetAxis("Vertical") * Time.deltaTime);
// Camera Ray casting
Ray cameraRay = mainCamera.ScreenPointToRay(Input.mousePosition);
Plane groundPlane = new Plane(Vector3.up, Vector3.zero);
float rayLength;
if (groundPlane.Raycast(cameraRay, out rayLength)) {
Vector3 look = cameraRay.GetPoint(rayLength);
Debug.DrawLine(cameraRay.origin, look, Color.red);
transform.LookAt(new Vector3(look.x, transform.position.y, look.z));
}
}
}
I want to be able to move the player using the WASD keys and also rotate following the direction on where the mouse is, however I don't want the rotation of the player to change the direction of the keys, I need the player to move forwards if the W key is pressed no matter which way the player is facing.
However for some reason my code makes the player move forwards depending on which way it is facing which I don't want.
How can I fix this?

The problem is that your transform.Translate call is in "self" space. Forward, backward, left, right are all relative to the direction the transform is facing. That is why your player is moving relative to the facing direction.
If you want to translate relative to "global" or "world" space, you have to add an additional parameter.
// player movement
transform.Translate(speed * Input.GetAxis("Horizontal") * Time.deltaTime,
0f,
speed * Input.GetAxis("Vertical") * Time.deltaTime,
Space.World);
Note the Space.World parameter at the end, to set the world coordinate system.
You can find more in the Unity docs here: https://docs.unity3d.com/ScriptReference/Transform.Translate.html

You need to look at the difference between local and global coordinate systems.
Right now your WASD keys are moving the player character according to global coordinates, and you want the WASD movement to be dependant on the player's orientation so you need to use a local coordinate system.
http://wiki.unity3d.com/index.php?title=Converting_Between_Coordinate_Systems

Rotate player with platform without parenting

I'm currently making a small platformer 3D game, but unfortunately I can't make the player to rotate properly when it is riding the platform, the thing here is that I don't want to make the player child of the platform, so far I've managed to make him move smoothly along with the platform, but the rotation is still going nowhere, here is the code I'm using for the rotation:
player.transform.rotation *= platform.rotation;
and here is the effect I got:
Rotation Error
not very nice :(
I guess the solution is something simple, some formula, but unfortunately I'm not very good with math :( So, thank you guys, I hope you can help me.

I'll show you a simple script example which makes a cube rotate by input while reacting to the rotation of the platform on which it stands:
using UnityEngine;
public class CubeRotation : MonoBehaviour {
public GameObject Platform;
Quaternion PreviousPlatformRotation;
public float rotationSpeed = 50;
private void Start() {
PreviousPlatformRotation = Platform.transform.rotation;
}
private void Update() {
//Rotate the cube by input
if (Input.GetKey(KeyCode.A)) {
transform.Rotate(Vector3.up, Time.deltaTime * rotationSpeed);
}
if (Input.GetKey(KeyCode.D)) {
transform.Rotate(Vector3.up, -Time.deltaTime * rotationSpeed);
}
//Adjust rotation due to platform rotating
if (Platform.transform.rotation != PreviousPlatformRotation) {
var platformRotatedBy = Platform.transform.rotation * Quaternion.Inverse(PreviousPlatformRotation);
transform.rotation *= platformRotatedBy;
PreviousPlatformRotation = Platform.transform.rotation;
}
}
}
The logic of the adjustment to the platform rotation is this:
Get at start the rotation quaternion of the platform (in your case, get it when the cube object climbs on the platform)
With A and D rotate the cube normally around the local Y axis.
Afterwards check if the platform's rotation has changed, if yes:
3.a Get how much the platform rotated since the previous frame, with the operation Actual rotation * Inverse(Previous Rotation); this operation it's akin to a difference between two quaternions
3.b Add that quaternion to the cube's rotation with the *= operator
3.c Set the platform's previous rotation value to the new one.
That's pretty much it.

How to fetch a rotation of a object while twisting it in Unity?

I am currently implementing a radio in Unity for Oculus. Player can twist the knob to change volume. However, either eulerangle or rotation cannot return a unique value while turning in 360 degrees.
And below code has the same problem with eulerangle.
void Start ()
{
oldRight = Vector3.right;
angle = 0.0f;
}
void Update ()
{
Vector3 right = transform.right;
float tempAngle = Vector3.SignedAngle(oldRight,right,transform.forward);
if (right.y < oldRight.y)
{
angle += tempAngle;
}
else
{
angle -= tempAngle;
}
oldRight = right;
}

transform.rotation
If you want XYZ angles (and not a quaternion),
transform.rotation.eulerAngles

First of all, we don't know what's the relation between the radio game object and the knob game object, and that matters.
I'll make an example in order to show how you can get the rotation of the knob regardless of that relation.
In the image below, the radio is the cube, with its transform reset all to 0.
This is the cylinder which acts as the knob:
The important part here is that I rotated and placed the cylinder such that the X axis of the transform is parallel to the X axis of the cube.
And here is the script that rotates the cylinder and reports the angle of such rotation:
using UnityEngine;
public class RotateKnob : MonoBehaviour {
public float m_Speed;
void Update() {
if (Input.GetKey(KeyCode.RightArrow)) {
transform.Rotate(Vector3.up, Time.deltaTime * m_Speed, Space.Self);
}
if (Input.GetKey(KeyCode.LeftArrow)) {
transform.Rotate(Vector3.down, Time.deltaTime * m_Speed, Space.Self);
}
var angle = Vector3.SignedAngle(transform.right, transform.parent.right, transform.up);
Debug.Log(angle);
}
}
Notice how the rotation is done relative to the Y axis and Space.Self.
The angle is taken relative to the Y axis of the cylinder (which is the axis around which we rotate the cylinder), thus transform.up as the SignedAngle third parameter, and ofc we measure the angle between the transform.right and the transform.parent.right (the transform.right of the cube that childs the cylinders).
With this code you don't have to worry about the transform of the cube in the world, the result will always be relative to the cube when rotating the cylinder.
Please do remember that the angle will be reported in the range [-180,180] and not [0,360].

Set player's boundary within sphere

I want to restrict player movement in the sphere, the schematic diagram show as below. If player movement is out of range, then restrict player to sphere max radius range.
How can I write C# code to implement it, like this?
These are my current steps:
Create 3D sphere
Create C# code append to sphere object
My code so far:
public Transform player;
void update(){
Vector3 pos = player.position;
}

I don't know how you calculate your player`s position but before assigning the new position to the player you should check and see if the move is eligible by
checking the new position distance form the center of the sphere
//so calculate your player`s position
//before moving it then assign it to a variable named NewPosition
//then we check and see if we can make this move then we make it
//this way you don't have to make your player suddenly stop or move it
//back to the bounds manually
if( Vector3.Distance(sphereGameObject.transform.position, NewPosition)< radius)
{
//player is in bounds and clear to move
SetThePlayerNewPosition();
}

What #Milad suggested is right but also include the fact you won't be able to "slide" on the sphere border if your movement vector even slightly goes outside the sphere :
(sorry for the crappy graphic skills...)
What you can do if you want to be able to "slide" on the sphere interior surface is get the angle formed between the player position and the X vector and then apply this angle with the :
public Transform player;
public float sphereRadius;
void LateUpdate()
{
Vector3 pos = player.position;
float angle = Mathf.Atan2(pos.y, pos.x);
float distance = Mathf.Clamp(pos.magnitude, 0.0f, sphereRadius);
pos.x = Mathf.Cos(angle) * distance;
pos.y = Mathf.Sin(angle) * distance;
player.position = pos;
}
Just make sure using this won't counter effect your player movement script (that's why I put it in LateUpdate() in my example).