Artillery Trajectory

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Artillery Trajectory

Post by Corporal Punishment » 15 Dec 2011, 01:58

I noticed recently something is off about WZ and Mortars. I have been wondering forever why it is that mortars fire into the flanks of hills they could easily shoot over. Now I think I know why: To make an educated guess, is it possible mortars use the same barrel elevation scale as howitzers? If so, this would be a fundamental flaw in the game.
The point is, mortars and howitzers employ a drastically different approach at ranging in. A howitzer alters barrel elevation (from about -2° to 65°) while a mortar has this pretty much fixed or at least alterable within rather narrow confines (usually around 45° to 80°). Both types of weapon also alter the quantity of propellant but while this is a secondary means to range in for howitzers, it is the primary method for mortars.
Now to the point: What are the maximum and minimum angels for barrel elevation for mortars and howitzers in WZ? And what other factors are taken into account to calculate trajectory? How is trajectory actually calculated?
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Re: Artillery Trajectory

Post by TVR » 15 Dec 2011, 05:22

If I recall correctly from the last time I checked the source, I found that the ballistic simulation system is extremely arbitrary:

1) Indirect units always try to fire at a ~30 degree elevation.

2) The elevation will not be adjusted for increased range, instead, the launch velocity of the projectile will be manipulated with infinite granularity to ensure the correct ballistic trajectory.

3) Should the target be within a few squares [not even minimum range, the number of squares is hard-coded], the indirect weapon will completely disregard maximum muzzle elevation and minimum range to fire at the high-angle ballistic fire solution.

4) There is no ballistic deflection calculation [leading for indirect weapons].

The 3.0 ballistic trajectory calculation code is better, but it still has infinite granularity of launch velocity.

I will rewrite the entire system in the future to actually respect the given limitations, yet be more accurate at the same time.

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Re: Artillery Trajectory

Post by Iluvalar » 15 Dec 2011, 08:09

TVR is not totally right

1- The weapons calculate his angle given the projectile speed in stat files.
1-A The low angle is under the horizon, the arty will take the high angle. (MRL Shooting like dumbs)
1-B The low angle is ok = Shoot.
1-C There is no such angle possible. The angle is set to 30° by default and it's the velocity that is modified. (ripples most of the time since nobody cared about giving it a speed that fit his range at start... XD)
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Re: Artillery Trajectory

Post by Corporal Punishment » 15 Dec 2011, 13:32

So the game modifies projectile speed to range in? That's just fine, it's what real-life artillery does by increasing or decreasing propellant quantity. So pretty much all it takes to make mortars and howitzers behave correctly is limit their barrel elevation to realistic values. Although, if I understand correctly, howitzers would still have a tendency to fire at 30° elevation. But then again, I never found howitzers to behave strange.
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Re: Artillery Trajectory

Post by Chojun » 15 Dec 2011, 16:26

At this point is where I begin to disagree with this. It's a game - the players want the IDF weapons to hit their targets, not neccessarily be realistic (although the case I've noticed where IDF weapons fire across the ground is dumb - I think the MRLS does this). The principal difference between mortars and howitzers in WZ is range and damage.

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Re: Artillery Trajectory

Post by Corporal Punishment » 15 Dec 2011, 21:15

That's exactly what I'm talking about. Mortars don't hit their targets because they behave incorrect. Take a urban map for example: How often does your mortar volley get stuck in a building? All the time! A realistic mortar would just fire over it and BAM!
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Re: Artillery Trajectory

Post by Chojun » 16 Dec 2011, 05:10

Ah I see. Sorry, I misinterpreted your original post. :P

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Re: Artillery Trajectory

Post by TVR » 16 Dec 2011, 05:43

As you know, propellant for artillery cannons are always supplied in the form of standardized, pre-measured bags, for the purposes of logistics and consistent internal ballistics. There are only a finite number of packaged propellant variations, which is proven by maximum MRSI capability, therefore there can not be infinite granularity in terms of varied muzzle velocity.

The quickest solution would be to have all indirect fire calculations default to the high-angle solution, in the future, I'll also add in the essential ability to switch between high-angle and low-angle ballistic fire solutions.

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Re: Artillery Trajectory

Post by Corporal Punishment » 16 Dec 2011, 13:17

Sure I know. I've been painting targets for'em for a living (among other nasty things)! Actually, there is only one type of charge. But you can load anything between one and, with most systems, eight charges into the chamber. On mortar grenades, the charges are inserted into the aft section that also serves as a stabilizer.
MRSI is limited not really by the propellant, as it relies more on barrel elevation, but much more by the duration of the loading cycle in relation to grenade flight time. On modern howitzers the concept of variable charges is utilized more for increasing flight speed on penetrator rounds these days. Artillerymen tend to use high charges as scarce as possible, since it drastically cuts down on barrel life expectancy. And, on a side note, grenade speed is also influenced by air pressure, wind, temperature and probably half a dozen other factors.
As I said, for mortars variations in propellant quantity are much more important. This is because it is a much simpler to handle means to adjust range and for the shorter ranges and lighter projectiles compared to howitzers mortar barrels are much more resilient towards high charges. On a side note, no mortar I am aware of has the MRSI capability. Maybe the Dragonfire 2 trialled by the USMC until 2009 could have done this, but there is no decisive information available and the program has been canceled.
However, for a game the assumption of infinite granularity of projectile speed should be a valid simplification because 1. Little to no players will have intricate knowledge on real life artillery. 2. On the given scale of the game, it makes no difference and 3. Nobody will even care.
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Re: Artillery Trajectory

Post by TVR » 17 Dec 2011, 21:47

As you (don't) know, the type of mortar used in Warzone 2100 is automatically loaded, with automatically adjusted 0-90 degree elevation, and automatic fire control, similar to, but not quite as advanced as the twin-barrelled, MRSI-capable AMOS turret, both which are incomparable to crew-served artillery, let alone infantry mortars.

Realism concerns aside, there is no real reason to arbitrarily adjust the muzzle velocity, when same function can be accomplished by adjusting the barrel elevation alone.

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Re: Artillery Trajectory

Post by Chojun » 18 Dec 2011, 00:06

I think the two of you have way more specific knowledge about field artillery than Pumpkin did.

I think Pumpkin just wanted an IDF weapon and put one in and called it a mortar. :wink:

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Re: Artillery Trajectory

Post by lav_coyote25 » 18 Dec 2011, 00:08

this is a game. pure and simple. not all the metrics need make sense. if your wanting ultra realism - play the jump and grunts. (fps).
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Re: Artillery Trajectory

Post by bendib » 18 Dec 2011, 00:32

Now I kinda agree with the OP. It's not so much about being realistic as it is having the weapon hit it's target unobstructed.
This isn't really about having an accurate weapon, it's more like a bug.
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Re: Artillery Trajectory

Post by Corporal Punishment » 19 Dec 2011, 01:21

TVR wrote:As you (don't) know, the type of mortar used in Warzone 2100 is automatically loaded, with automatically adjusted 0-90 degree elevation, and automatic fire control, similar to, but not quite as advanced as the twin-barrelled, MRSI-capable AMOS turret, both which are incomparable to crew-served artillery, let alone infantry mortars.

Realism concerns aside, there is no real reason to arbitrarily adjust the muzzle velocity, when same function can be accomplished by adjusting the barrel elevation alone.
I am aware that WZ mortars are breech-loader types, yes. Such systems are not really new, heavy mortars above 120mm caliber always employed breech loader mechanisms, although such weapons are rare to non-existent in modern arsenals. The AMOS, which honestly I was not aware of yet, is a interesting concept both as a role-model for WZ and for it's implications for future overseas engagements. It is more or less exactly what we missed back in my day, a highly mobile highly potent artillery platform that goes into a C-130. Although it does not match the standing definition of a mortar, that is a weapon which fires at 45° or higher elevation. It also does not match the standing definition of a howitzer, which is a weapon that fires at angles up to ~65° elevation. Or, to put the other way around: It matches both definitions. From my understanding, it is a completely new type of artillery piece. Then again, if it is officially called a mortar, who am I to object? So let's assume WZ mortars are something like it and let's further assume WZ howitzers are, too. Only bigger. Under these premises your solution is perfectly valid.

Today I came to think, it is moot to discuss changes in the way artillery in WZ works to solve the issue of mortar volleys getting stuck in obstacles, anyway. If you think about it, other weapons tend to do this, too. Only in the case of direct fire weapons the strange behavior is they fire against hills because there is a target around the corner and they don't realize line of fire is broken. Terrain is notoriously inconsistent now that I think of it. Under some other circumstances projectiles travel through hills unhindered. So the underlying problem is that there are issues with obstacle recognition.
From my work with GIS I understand terrain surface is represented in a vector environment as a two-dimensional warped plane, usually in the shape of a triangular irregular network. Of course points on that surface have three-dimensional coordinates, but the plane itself is two-dimensional in having no thickness. I guess WZ handles it the same, only it uses a rectangular regular network. Now, this warped plane must have some functionality that lets WZ know it is solid. Only this is not reliable as in some cases it is not recognized by the algorithm that determines trajectory but by that which determines projectile impact and in others it is not recognized by both.
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Re: Artillery Trajectory

Post by stiv » 19 Dec 2011, 08:40

I've noticed where IDF weapons fire across the ground is dumb - I think the MRLS does this
This change was made awhile back because someone didn't like the fact that MRLS fired in a very high (but kinda sorta ballistically correct) trajectory when firing on near-by targets - so it was made into a direct-fire weapon. Kind of dumb, IMHO. But then I like the whole gravity's rainbow thing.

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