Raycast to follow an object on one axis, and another on a different axis

Question

Hi there.

Right now I'm trying to get a raycast to always aim straight ahead of it's origin point, but be able to angle up and down on a single axis depending on where a separate object is located.

I've thought I had it numerous times, but I seem to be pulling up just short of a solution. I'm using DrawLine to see what I'm doing for the moment. Here's my current attempt, with all the irrelevant stuff cut out:

 var weaponFocus =         bulletTarget.transform.position; //This is the object the ray should be following.
 var rayCastPos =          weaponRifle.transform.position;
 var weaponDirection =     weaponRifle.TransformDirection(Vector3.up); //The model I'm using has it's up position at the end of the barrel, so Vector3.up is actually forward. Woops.
 var weaponFocusLimitedX = weaponDirection.x;
 var weaponFocusLimitedY = weaponDirection.y;
 var weaponFocusLimitedZ = weaponDirection.z;
 
 Debug.DrawLine(rayCastPos,Vector3(weaponFocusLimitedX,weaponFocusLimitedY,weaponFocus.z).normalized * 100, Color.red,0.0,true);

The basics of what I'm trying to accomplish here is to have the ray head straight forward from the weapon, but be able to move up and down to follow a target. I don't want it following the target left or right, however.

Any help with this is greatly appreciated.

Answer 1

Best Answer

Answer by robertbu · Aug 10, 2014 at 05:15 AM

Okay. Given your description, I'm assuming you are projecting a targeting point into 3D space from the mouse. I'm also going to assume you've fixed your rotation, since dealing with a non-standard rotation is difficult for me to think through.

hitPoint - the point projected into 3D space by the mouse position
adjustedPoint - a point in front of the gun to use for your targeting
adjustedDir - the direction from the gun to the point (may not need)

var pt : Vector3 = ProjectPointOnPlane(gun.up, gun.position, hitPoint); var fwdDist : float = (pt - gun.position).magnitude; var up : Vector3 = (hitPoint - pt); var adjustedPt : Vector3 = gun.forward * fwdDist + up; var adjustedDir : Vector3 = adjustedPt - gun.position;

function ProjectPointOnPlane(planeNormal : Vector3 , planePoint : Vector3 , point : Vector3 ) : Vector3 { planeNormal.Normalize(); var distance = -Vector3.Dot(planeNormal.normalized, (point - planePoint)); return point + planeNormal * distance; }

This (untested) code works by swinging the targeting point you get from your mouse around so that it is in front of the camera. It gives you a point to aim at or to use in a Linecast() or as a step in creating a direction.

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Barachiel · Aug 10, 2014 at 06:43 AM 0

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I'm not currently at my work station so I can't test this right away, but that certainly looks like something I can work with.

In order to do a couple of other interesting things, the point I have the ray aimed at is a sphere with the mesh renderer turned off (the renderer only continues to exist for visual debugging now and then). The sphere is a child of an empty game object that follows the mouse position (it also has a plane with some scripts for crosshairs and the like).

Do you foresee any major issues when applying your solution to this situation?

Thanks for your time so far. =)

robertbu · Aug 10, 2014 at 11:20 AM 0

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As long as the aiming point is in 3D space in front of the camera, the code should work. Let me explain conceptually. Imagine there is a plane running through the gun with the plane normal facing up. For example, if the gun up was aligned with the world up, then this would be the XZ plane. Now project the aiming point on plane plane. Next a distance is measured from the gun to the projected point on the plane, and a vector is created from the plane up to the aiming point. Finally we construct a new aiming point that walks out the transform.forward the measured distance, then uses the vector to move up. So the final point will be directly in front of the gun but at right height.

Barachiel · Aug 11, 2014 at 11:40 AM 0

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Hello again. Turns out it's a public holiday today for some local show, but I did run a small test to try out your solution.

Here's the code.

gunMuzzleObj is just an empty game object representing the muzzle position of the gun, as one would expect.
bulletTarget is a sphere for aiming, in the same sort of setup I have for the crosshair.

 var pt : Vector3 =           ProjectPointOnPlane(gunMuzzleObj.transform.up, gunMuzzleObj.transform.position, bulletTarget.transform.position);
 var fwdDist : float =        (pt - gunMuzzleObj.transform.position).magnitude;
 var up : float =             (bulletTarget.transform.position - pt).magnitude;
 var adjustedPt : Vector3 =   gunMuzzleObj.transform.forward * (fwdDist + up);
 var adjustedDir : Vector3 =  adjustedPt - gunMuzzleObj.transform.position;
 
 function ProjectPointOnPlane(planeNormal : Vector3 , planePoint : Vector3 , point : Vector3 ) : Vector3
 {
     planeNormal.Normalize();
     var distance = -Vector3.Dot(planeNormal.normalized, (point - planePoint));
     return point + planeNormal * distance;
 }

The results seem kind of similar to what I've seen with my own attempts, with it seeming mostly accurate until you start to move around.

This is how it looks just aiming at a pillar/barrel thing from the starting position: alt text

And this is how it looks as I move around and aim at different spots: alt text

alt text

It seem to try it's hardest to match the target's position vertically (relative to the screenshots), but often falls short. Horizontally, it couldn't care less about.

robertbu · Aug 11, 2014 at 12:35 PM 0

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My fault. I had the wrong type on 'up' in my code fragment (now fixed) and confused you. Your line 3 should be:

  var up : Vector3 = bulletTarget.transform.position - pt;

...and then line 4 would be:

  var adjustedPt : Vector3 = gunMuzzleObj.transform.forward * fwdDist + up;

'up' is the vector from the point on the plane to the target point.

Barachiel · Aug 11, 2014 at 01:31 PM 0

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Ah, there we go, that works much better. I seem to have gone the polar opposite than I should have when fixing that third line, woops. I should have thought to try both.
It aims in the right direction now and doesn't swing wildly about like my own poor attempts, but it seems to be aiming at a point further down and in front of the target than it should be. I'm sorry to keep bugging you, but I feel a little out of my depth here. Looking over the code, based on what I know (and have now learned) I don't see what's causing this.

Here's a couple of screens of what I mean:

alt text