Need help getting a 3d guided missile to work

BevanFindlay

I am trying to make a game that lets you fly spacecraft in 3d, using Newtonian physics. Going well so far, except I cannot seem to get the guided missile to work. Have tried a bunch of things and none of them work.

If I try and set rotation or set a transform (as per some examples I found), the missile locks in place and will not move (I have a feeling this may be related to how the docs say not to directly set things like the velocity every frame?) But, I am wanting the missiles to be a little slow at turning anyway (rather than perfectly track a target), so have been using add_torque( ) to try and steer the missile towards its target.

At first I tried converting to local coordinates and applying x and y torques, though the code got messy so I switched back to trying the, hopefully simpler, directly working with global coordinates. But in both cases, the missiles seem to in completely the wrong directions. Also, why is there not a "to global coordinates" and "to local coordinates" on everything? Transforms do give you more power, but are much harder to work with and make for much messier, harder-to-read code.

Some of the things I tried are below. Any suggestions would be appreciated. TIA.

target_heading = translation - target_object.translation
current_heading = global_transform.basis.z
target_heading =  current_heading.normalized() - target_heading.normalized()

add_torque(target_heading * TORQUE)

and

if target_heading.x > 0:
	add_torque(Vector3(-TORQUE, 0, 0))
elif target_heading.x > 0:
	add_torque(Vector3(TORQUE, 0, 0))
if target_heading.y > 0:
	add_torque(Vector3(0, -TORQUE, 0))
elif target_heading.y > 0:
	add_torque(Vector3(0, TORQUE, 0))
if target_heading.z > 0:
	add_torque(Vector3(0, 0, -TORQUE))
elif target_heading.z > 0:
	add_torque(Vector3(0, 0, TORQUE))

TwistedTwigleg

Welcome to the forums @BevanFindlay!

Also, why is there not a "to global coordinates" and "to local coordinates" on everything? Transforms do give you more power, but are much harder to work with and make for much messier, harder-to-read code.

You can convert positions from local and global coordinates using Transform.xfrom and Transfrom.affine_inverse().xform. That said, having worked with a lot of transforms and converting between various spaces, it is rather confusing and the code isn't straightforward.

I've found that one of the ways to help make it a little easier is to make helper functions with names like to_global_transform and to_local_transform, as then the conversions are a bit more readable.

Some of the things I tried are below. Any suggestions would be appreciated. TIA.

target_heading = translation - target_object.translation
current_heading = global_transform.basis.z
target_heading =  current_heading.normalized() - target_heading.normalized()
add_torque(target_heading * TORQUE)

I think the issue with this snippet is that translation is the position offset of the object relative to it's parent node. If both nodes have the same parent node then the first line of code will give you the direction from the object to the target, but if they have different parents then it will not work correctly.

I'd recommend using something like this for the first line of code:

target_heading = global_transform.origin - target_object.global_transform.origin
# or
# target_heading = global_transform.origin.direction_to(target_object.global_transform.origin)
# the code above will return a normalized vector but otherwise is the same

Then it might work, though I'm not positive.

Something else you could try if setting the transforms directly works, is still calculating the transforms but instead of directly setting them you interpolate the current transform with the desired transform. This will dampen the rotation a bit, making it not snap in place perfectly when tracking the target.

You could then have the rotation interpolated, and the position modified by moving towards the forward direction of the missile. I believe this would also achieve the desired effect with having the missile slower at turning while still attempting to reach the target.

For moving it and/or setting the velocity directly, you generally want to use the _integrate_forces function for this, as then it will be in sync with the physics engine. :+1:

epicspaces

https://kidscancode.org/godot_recipes/ai/homing_missile/

BevanFindlay

@epicspaces said: https://kidscancode.org/godot_recipes/ai/homing_missile/

This is only a 2D example, and is very different to doing it in 3D. 2D is much more simple.

epicspaces

@BevanFindlay said:

@epicspaces said: https://kidscancode.org/godot_recipes/ai/homing_missile/

This is only a 2D example, and is very different to doing it in 3D. 2D is much more simple.

even 3d is simple, just add z to your vector3 what do you thought, I used this code in my 3d games you kow