Orient vehicle to ground normal (terrain hugging)

Question

So the problem I'm having is trying to orient a vehicle to the ground based on a raycast. The raycast works, the movement works, and aligning the normal of the ground to the transform.up works. However, together these don't work. It won't rotate.

alt text

I think the problem is that aligning the transform.up = hit.normal overrides any rotation. My question would be, how exactly do I form an algorithm that will translate rotation into the normal. I figure if I can rotate the normal before I set it to the up vector that rotation should be possible. And I don't want it to rotate and snap back, which I found out how to do.

Here is my code (C#):

 if (Physics.Raycast(transform.position, -transform.up, out hit))
     {
         Quaternion grndTilt = Quaternion.FromToRotation(transform.up, hit.normal);
         transform.rotation = Quaternion.Euler(0, Input.GetAxis("Horizontal") * turnSpeed * 100 * Time.deltaTime, 0) * grndTilt;
         //transform.up = hit.normal;    
     }
     Vector3 movDir;
     //transform.Rotate(0, Input.GetAxis("Horizontal") * turnSpeed * Time.deltaTime,0);
     movDir = transform.forward*Input.GetAxis("Vertical")*speed;
     // moves the character in horizontal direction
     controller.Move(movDir*Time.deltaTime-Vector3.up*0.1f);

I've been all over the internet, and nothing seems to be working!

EDIT:

Removed the code because it was incorrect. The solution:

Two parts - a composite vector from each of the corners to give you the direction to orient (my original issue) - and separating the mesh to a sub gameobject. Keep your controller as the root (or even another sub object). Very clean movement. Forgive me for no code example. :)

Answer 1

Answer by Thoras_Bublyk · Feb 14, 2015 at 06:15 PM

Hey folks!!! After many hours of research i got it. In your Update function manually increment Y angle of your object and manually set rotation after align. Excellent!!!

     float objYangle;
         
         void Start(){
         objYangle=transform.eulerAngles.y;
         }
         
         void Update() {
         objYangle +=  Input.GetAxis("Horizontal") * turnSpeed;
         
         SirGiveMagicAlignFunction(); //first answer by mr SirGive
         
         transform.Rotate(0, objYangle, 0); //and finally set current angle
         
         }

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Answer 2

Answer by FlightOfOne · Jul 12, 2017 at 09:16 PM

This thread really helped me out with this problem. I have combined what @SirGive and @EasyKill showed and created this method. This is the most smoothest and predictable way that worked for me. I am using this in vehicle (using with Navmesh Agent). Hope this helps someone.

See final outcome here

  void AlignWithSurface(Transform _parent, Transform _hull, LayerMask _checkLayer, float _maxCheckDist =30, float _rate=0.1f)
     {
 
         RaycastHit frHit,flHit,rrHit,rlHit;
 
         Physics.Raycast(fr.position + Vector3.up, -Vector3.up, out frHit, _maxCheckDist, _checkLayer);
         Physics.Raycast(fl.position + Vector3.up, -Vector3.up, out flHit, _maxCheckDist, _checkLayer);
         Physics.Raycast(rr.position + Vector3.up, -Vector3.up, out rrHit, _maxCheckDist, _checkLayer);
         Physics.Raycast(rl.position + Vector3.up, -Vector3.up, out rlHit, _maxCheckDist, _checkLayer);
 
         Vector3 a = rrHit.point - rlHit.point;
         Vector3 b = frHit.point - rrHit.point;
         Vector3 c = flHit.point - frHit.point;
         Vector3 d = rrHit.point - flHit.point;
 
         // Get the normal at each corner
 
         Vector3 crossBA = Vector3.Cross(b, a);
         Vector3 crossCB = Vector3.Cross(c, b);
         Vector3 crossDC = Vector3.Cross(d, c);
         Vector3 crossAD = Vector3.Cross(a, d);
 
         Vector3 _upNew = (crossBA + crossCB + crossDC + crossAD).normalized;
 
         Quaternion _newRot= Quaternion.LookRotation(Vector3.Cross(_parent.right, _upNew).normalized, _upNew); //If parented
         //Quaternion _newRot = Quaternion.LookRotation(_hull.forward, _upNew); //If NOT parented
 
         _hull.rotation = Quaternion.Lerp(_hull.rotation, _newRot, _rate);
 
     }

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jobo22 · Oct 05, 2018 at 11:53 PM 0

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Hi @FlightCrazed I see your video and it is exactly what I'm trying to accomplish. I also have a tank that I want to align to the terrain. I copied your script and made public transforms for the corners of my tank and of my main tank that I assigned in the inspector. I call the AlignWithSurface() function in Update(), but it's not working. Sometimes my tank will rock a little bit side to side, but it won't go up and down when it goes up or down a hill. I use the line for not parented. Any help would be appreciated. Thanks! :)

FlightOfOne jobo22 · Oct 06, 2018 at 03:34 PM 1

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Hi There, this is the whole file. I do have something called move to ground in there. Also be sure that the max distance (length of the rays) can actually reach the ground.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 /// <summary>
 /// Orientates the objects to align with the surface
 /// </summary>
 public class VehicleSurfaceOrientator : $$anonymous$$onoBehaviour {
     public Transform fl, fr, rl, rr;
     public Layer$$anonymous$$ask ground$$anonymous$$ask;
     private RaycastHit _groundHit;
     private void Update()
     {
        
         AlignWithSurface(transform, transform, ground$$anonymous$$ask);
         $$anonymous$$oveToGround();
     }
 
     void $$anonymous$$oveToGround()
     {
         if(Physics.SphereCast(transform.position+Vector3.up,1,Vector3.down,out _groundHit,100,ground$$anonymous$$ask))
         {
             transform.position = _groundHit.point;
         }
     }
 
     /// <summary>
     /// </summary>
     /// <param name="_parent"></param>
     /// <param name="_hull"></param>
     /// <param name="_checkLayer"></param>
     /// <param name="_maxCheckDist"></param>
     /// <param name="_rate"></param>
     void AlignWithSurface(Transform _parent, Transform _hull, Layer$$anonymous$$ask _checkLayer, float _maxCheckDist = 30, float _rate = 0.1f)
     {
 
         RaycastHit frHit, flHit, rrHit, rlHit;
 
         Physics.Raycast(fr.position + Vector3.up, -Vector3.up, out frHit, _maxCheckDist, _checkLayer);
         Physics.Raycast(fl.position + Vector3.up, -Vector3.up, out flHit, _maxCheckDist, _checkLayer);
         Physics.Raycast(rr.position + Vector3.up, -Vector3.up, out rrHit, _maxCheckDist, _checkLayer);
         Physics.Raycast(rl.position + Vector3.up, -Vector3.up, out rlHit, _maxCheckDist, _checkLayer);
 
         Vector3 a = rrHit.point - rlHit.point;
         Vector3 b = frHit.point - rrHit.point;
         Vector3 c = flHit.point - frHit.point;
         Vector3 d = rrHit.point - flHit.point;
 
         // Get the normal at each corner
 
         Vector3 crossBA = Vector3.Cross(b, a);
         Vector3 crossCB = Vector3.Cross(c, b);
         Vector3 crossDC = Vector3.Cross(d, c);
         Vector3 crossAD = Vector3.Cross(a, d);
 
         Vector3 _upNew = (crossBA + crossCB + crossDC + crossAD).normalized;
 
         Quaternion _newRot = Quaternion.LookRotation(Vector3.Cross(_parent.right, _upNew).normalized, _upNew); //If parented
         //Quaternion _newRot = Quaternion.LookRotation(_hull.forward, _upNew); //If NOT parented
 
         _hull.rotation = Quaternion.Lerp(_hull.rotation, _newRot, _rate);
 
     }
 }

jobo22 FlightOfOne · Oct 08, 2018 at 06:12 PM 0

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Thank you so much! I got it all working, you saved me hours of frustration and I got exactly what I was wanting! :)

Orient vehicle to ground normal (terrain hugging)

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