OFP Physics Equations

[Homefry 0]

For some time now I've been trying to figure out exactly what equations BIS used to calculate physics in OFP. The main equation I'm after is the equation for freefall objects, such as bombs released from aircraft. I've messaged Suma before, and was told:

Quote[/b] ]

The realistic one - gravity causes acceleration 9.066 m/s^2. The speed of the falling objects however depends on other things as well, mostly air friction.

Perhaps there is someone floating around the OFP world that was a physics major in college? I took physics in high school, and understand general things, but I never learned how to equate for air resistance and the like. Any help or ideas would be great.

[deanosbeano 0]

along time ago in bis forums a group, did a big test on the physics on ofp, mainly on bullets i think ,maybe you can search it, sorry i dont have time

good luck

found this called quantum

quantum

[Doolittle 0]

A lot of work was put into trying to figure out that very thing you ask.

Check out http://www.flashpoint1985.com/cgi-bin....94;st=0 and http://www.flashpoint1985.com/cgi-bin....iew=new... and the end result of all of this was Dinger from Chain of Command and their Universal Artillery, though I believe this relies on range tables, not on a single equation.

Doolittle

[[aps]gnat 28]

Below is part of my upcoming Virtual Bomber addon.

It resonably predicts when a level flying Bomber should release its bomb load.

<table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Code Sample </td></tr><tr><td id="CODE">

_DropMark = _BomberLead + (sqrt((2 * _BomberHeight)/9.8) * _BombFactor)

#dropbomb2

~0.1

_Abort = _Abort + 1

?(_Abort > 4200) : goto "AbortRun"

_BomberXpos = ((getpos (leader _TeamX)) select 0)

_BomberYpos = ((getpos (leader _TeamX)) select 1)

_BomberDistance = Sqrt(((_MarkerXpos-_BomberXpos)^2)+((_MarkerYpos-_BomberYpos)^2))

_HSpeed = (speed vehicle (leader _TeamX)*1000)/(60*60)

?(_BomberDistance > (_DropMark * _HSpeed )) : goto "dropbomb2"

#ReleaseBomb

"[_x,_weapon,_ammoname,_dropnumber,_dropdelay] exec {\GNT_VBomber\dropbombs.sqs}" forEach _BGroup

goto "AReturn"

Ignore _BomberLead and _Bombfactor, these are not critical to the calculation, only "adjusters". _TeamX is the bomber.

The bomb "sidefriction" config can effect this greatly but I have not been able to convert BIS's number into an adjusting formula. For most free fall bombs (friction ~0.2) the above works well enough.

[Homefry 0]

@deanosbeano:

Thanks for the link mate, there seems to be a lot of information in there.

@Doolittle:

All two threads are proving very helpful, and since I've tried UA, I can attest to the accuracy of what you guys did. I'll see if I can't come up with something typing the range tables together perhaps... we'll see.

@[APS]Gnat

This "sidefriction" value in the config.... well that's pretty interesting. I wonder what would happen if we changed that value to 0... wouldn't that help figure something out?

[[aps]gnat 28]

I wonder what would happen if we changed that value to 0... wouldn't that help figure something out?

Sure, but the Virtual Bomber addon is an addon to take advantage of OTHER peoples bomber addons, hence I don't have control over their bombs config, I just need to know what it is and manually adjust the calculation with a "factor".

[Doolittle 0]

What about finding an object that friction doesn't effect. Does air friction affect cameras? Or furniture, or shell ejections?

[UNN 0]

The closes thing I've seen to a Drag Coefficient in OFP uses this iterative method:

<table border="0" align="center" width="95%" cellpadding="0" cellspacing="0"><tr><td>Code Sample </td></tr><tr><td id="CODE">_TargetHeight= _This select 0

_IntAngle = _This select 1

_CurrCd = _This select 2

_IntVelocity= _This select 3

_CurrRange = _This select 4

_Index = _This Select 5

_Reverse = _This Select 6

;Initialise local variables

_TimeInt = 0.1

_IntRho = 0.1

_Gravity = 9

_XPos = 0

_YPos = 0

_DelX = 0

_DelY = 0

_DelVx = 0

_DelVy = 0

_Angle = 0

_FlightTime = 0

_InFlight = True

_Return = [0,0]

_Rho = _IntRho

_Velocity = _IntVelocity^2

_Angle = _IntAngle

_Vx = _IntVelocity*Cos(_Angle)

_Vy = _IntVelocity*Sin(_Angle)

_CurrCd = _CurrCd / 10000

_XPercentage= (_CurrRange / 100)*80

;Calculate the trajectory

#InFlight

@(True)

;Calculate how much of the velocity is lost to drag and gravity

_DelVx = (-_TimeInt*((_Rho*_CurrCd)))*_Velocity*Cos(_Angle)

_DelVy = -_TimeInt*_Gravity-(_TimeInt*(_Rho*_CurrCd))*_Velocity*Sin(_Angle)

;Over a period of 0.1 seconds

_DelX = _TimeInt*(_Vx+_DelVx)

_DelY = _TimeInt*(_Vy+_DelVy)

;Adjust the velocity

_XPos = _XPos+_DelX

_YPos = _YPos+_DelY

;Increment the time in flight

_FlightTime = _FlightTime+_TimeInt

;The trajectory has hit the ground so store the result and end the loop

If !(_Reverse) Then {If ((_YPos < _TargetHeight) and (_XPos > _XPercentage)) then {_InFlight = False; _Return = [_XPos,_FlightTime]}} Else {if (_YPos < _TargetHeight) then {_InFlight = False; _Return = [_XPos,_FlightTime]}}

;Prepare for the next time slice

_Rho = _IntRho*Exp(-0.000057*_YPos)

_Angle = ATan(_DelY/_DelX)

;Reposition the round according to the new velocity

_Vx = _Vx+_DelVx

_Vy = _Vy+_DelVy

;Calculate the new velocity

_Velocity = (_Vx^2)+(_Vy^2)

;See if the shell has landed

If (_InFlight) Then {goto "InFlight"}

;Save the result to the array

[_Index,+_Return,FCU_TRAJECTORY] Call FCU_SetIndexStatus

;Tell GroupRange.sqs we have a result

[_Index,False,FCU_CALCULATING] Call FCU_SetIndexStatus

CurrCd is the coefficient and comes out as 0.00525. I got gravity to 9, so not far off the 9.22 as quoted by Suma. With a bit of trial and error, varying the cofficent lets me adjust the trajectory for different addons.

Might not help much with a virtual bomber, as it takes a few seconds to calculate an impact point even at short ranges like 2500 meters.