Terrain movement penalties

[Axe99]

One of my (many) lasting memories of HoI3 is what happens to fuel-dependent units if they get caught out of supply and run out of fuel in a swamp. Not pretty, at all, and I haven't had anything remotely like that happen in HoI4 (even just being held up in a swamp, for a start - obviously running out of fuel isn't a thing). Hadn't really looked into it closely though, but I just went looking for the weather combat modifiers because someone had raised the issue in another thread and thought I'd have a quick look at the terrain file as well, and tripped over something that looked a little odd - in that all the terrain movement modifiers seem to have been 'hashed out'.

Except from terrain file (from the vanilla game, so modding isn't an element) looks like:

Spoiler

    forest = {
        color = { 89 199 85 }
        movement_cost = 1.5
        combat_width = -0.20
        ai_terrain_importance_factor = 5.0
        sound_type = forest

        units = {
            attack = -0.2
            #movement = -0.2
        }

        enemy_army_bonus_air_superiority_factor = -0.1
    }

    hills = {
        color = { 248 255 153 }
        movement_cost = 1.5
        combat_width = -0.33
        ai_terrain_importance_factor = 3.0
        sound_type = desert

        units = {
            attack = -0.3
            #movement = -0.2
        }
        enemy_army_bonus_air_superiority_factor = -0.05
    }
  
    mountain = {
        color = { 124 135 125 }
        movement_cost = 2.0
        attrition = 0.4
        combat_width = -0.66
        ai_terrain_importance_factor = 10.0
        sound_type = desert

        units = {
            attack = -0.6
            #movement = -0.4
        }

        enemy_army_bonus_air_superiority_factor = -0.10
    }
  
    plains = {
        color = { 255 129 66 }
        movement_cost = 1.0
        ai_terrain_importance_factor = 0.1
        sound_type = plains
    }
  
    urban = {
        color = { 155 0 255 }
        movement_cost = 1.2
        ai_terrain_importance_factor = 4.0
        sound_type = plains

        units = {
            attack = -0.3
            #movement = -0.2
        }

        enemy_army_bonus_air_superiority_factor = -0.50
    }
  
    jungle = {
        color = { 127 191 0 }
        movement_cost = 1.5
        attrition = 0.3
        combat_width = -0.25
        ai_terrain_importance_factor = 6.0
        sound_type = forest

        units = {
            attack = -0.3
            #movement = -0.3
        }

        enemy_army_bonus_air_superiority_factor = -0.25
    }  
  
    marsh = {
        color = { 76 96 35 }
        movement_cost = 2.0
        attrition = 0.5
        combat_width = -0.25
        ai_terrain_importance_factor = 8.0      
        sound_type = forest

        units = {
            attack = -0.4
            #movement = -0.4
        }
    }

There are also movement penalties in the unit files as well - so the terrain file isn't the be all and end all, but these don't seem to be the 'full' harshness one would expect (for example, MOT in marsh is only -30 per cent, oddly (at least to me) less harsh than forests, at -50 per cent movement, and there's no penalty to MOT movement in mountains).

Couple of questions:
- Has anyone noticed terrain slowing their movement? If yes, were there any tooltips indicating by how much?
- Does anyone know if movement penalties for terrain are maybe hidden away somewhere else other than the terrain and unit files?

And, more broadly, what do people think about the current impact of terrain on movement in-game - does it 'feel' right, or if it doesn't, what seems off? It's the ease of travelling through marshes, for example, that had me wondering exactly what was going on, and where this thread came from.

 

[Alex_brunius]

It appears the "hashed out" values were replaced with "movement_cost" instead in the same file. 1.5 movement cost from for example forest means it "costs" 1.5 times more time to move the same distance then it would in plains.

This movement cost modifier isn't shown in the ingame UI for how many km/h units move, but it is actually used to determine the final time a move takes. ( I have been able to verify this with testing a modded game ).

The reason for this ( judging by what devs wrote back in HoI3 and how terrain map files look in [map/terrain.bmp] ) is because terrain inside the same province actually can differ, and only the majority is "shown" in the UI and used for combat penalty ( and unit type movement penalty ) calculations. But as a unit travels between the center pixels of two provinces the speed from the movement_cost along the line can change depending on the actual terrain on the pixel the unit moves over ( which doesn't have to be the same as the majority terrain of the province ).

This is another reason why the terrain can look wrong or strange in some places of the world, or like it doesn't fit exactly with province borders, because under the hood it actually don't!


Edit: Actually it is shown here ingame:

 

[jamesd]

One of the key things to remember is that almost all movement by divisions is done on roads, and so infrastructure should play a very big part in unit movement speeds. If your division is on a German Autobahn that passes through a swampy province, the impact on movement speed should be rather minimal. A unit with heavy equipment, be it horse or vehicle towed, moving cross country is going to face obstacles like streams, woods, buildings & fences, and even in a swampy province, there's going to be some dry land between bodies of water, so when assessing the impact of terrain on movement rates, you need to consider that even in clear terrain, its unusual to find a large flat, hard piece of ground that allows rapid movement off roads - the Libyan-Egyptian desert between the sea and the inland sand sea being possibly the biggest exception.

As to movement speeds in general, this was discussed in depth on another thread a month or two ago and what was discovered was that movement rates in game are too high. For example US infantry doctrine calls on troops to march 2.5mph (4kmh) for 6-8 hours a day, however HOI4 seems to be letting units march 12 hours a day. To contrast US doctrine, they actually called on troops to march further per day than that of the German & Russian doctrines, and in practice those other doctrines were more sustainable, meaning that a more realistic speed for operational movement (as opposed to strategic movement) in game would be closer to 2 kmh. I'd probably limit towed Art etc to 2kmh and infantry to 2.5kmh. Vehicle speeds needed to be reduced in a similar fashion.

 

[Alex_brunius]

One of the key things to remember is that almost all movement by divisions is done on roads, and so infrastructure should play a very big part in unit movement speeds. If your division is on a German Autobahn

The problem is that infrastructure in HoI4 doesn't necessarily represent roads or highway... It can also represent for example a large main railroad line running through tunnels and bridges in a mountain pass.

This would be to very little help for units trying to pass said mountain on foot ( and only boost their Strategic redeployment speed ).

To be honest I kind of liked the HoI3 and HoI2 approach a bit better here where infrastructure didn't impact unit movement speeds at all except for when doing SR, since this allows infrastructure to represent railroads more closely which is what is important for supply transfer.

meaning that a more realistic speed for operational movement (as opposed to strategic movement) in game would be closer to 2 kmh. I'd probably limit towed Art etc to 2kmh and infantry to 2.5kmh. Vehicle speeds needed to be reduced in a similar fashion.

In practice after you take terrain penalties, infrastructure penalties, and the terrain movement cost into account infantry shouldn't move faster then 2km/h in most situations in HoI4.
But I am not sure the speed shown can be 100% trusted to scale with real distances and speeds, but they probably end up fairly close.

It does feel to me that units do move a bit too fast so I agree with the feeling you have.

 

[Axe99]

It appears the "hashed out" values were replaced with "movement_cost" instead in the same file. 1.5 movement cost from for example forest means it "costs" 1.5 times more time to move the same distance then it would in plains.

This movement cost modifier isn't shown in the ingame UI for how many km/h units move, but it is actually used to determine the final time a move takes. ( I have been able to verify this with testing a modded game ).

The reason for this ( judging by what devs wrote back in HoI3 and how terrain map files look in [map/terrain.bmp] ) is because terrain inside the same province actually can differ, and only the majority is "shown" in the UI and used for combat penalty ( and unit type movement penalty ) calculations. But as a unit travels between the center pixels of two provinces the speed from the movement_cost along the line can change depending on the actual terrain on the pixel the unit moves over ( which doesn't have to be the same as the majority terrain of the province ).

This is another reason why the terrain can look wrong or strange in some places of the world, or like it doesn't fit exactly with province borders, because under the hood it actually don't!


Edit: Actually it is shown here ingame:
View attachment 263365

Cheers Alex, a little embarrassed I missed the movement_cost in the other block, very much appreciate you pointing it out . Best I go back to looking at stuff that floats again now .

On the movement speed thing, it definitely feels a bit quick at times (particularly through swamps - I've never really noticed the Pripet Marshes, to the point that before I used the better terrain mod, I'd literally forgotten they were there - which is very different from my experience with them in HoI3 or WitE, when they were very noticeable). While you're quite right @jamesd that if there's an autobahn running through the marshes it wouldn't make much of a difference, at this point in time the actual means of travel through the Pripet marshes at least were (as far as I understand it) pretty limited. That said, I'm hardly an expert (I wouldn't even qualify as a novice at this stage), and will happily defer to others on this .

 

[jamesd]

The problem is that infrastructure in HoI4 doesn't necessarily represent roads or highway... It can also represent for example a large main railroad line running through tunnels and bridges in a mountain pass.

This would be to very little help for units trying to pass said mountain on foot ( and only boost their Strategic redeployment speed ).

To be honest I kind of liked the HoI3 and HoI2 approach a bit better here where infrastructure didn't impact unit movement speeds at all except for when doing SR, since this allows infrastructure to represent railroads more closely which is what is important for supply transfer.

In practice after you take terrain penalties, infrastructure penalties, and the terrain movement cost into account infantry shouldn't move faster then 2km/h in most situations in HoI4.
But I am not sure the speed shown can be 100% trusted to scale with real distances and speeds, but they probably end up fairly close.

It does feel to me that units do move a bit too fast so I agree with the feeling you have.

For that other thread, I ran some tests comparing real world distances to speed x time in game to come to the estimate that Paradox was allowing units around 12 hours a day for movement at their specified movement rates. The in game rate of 4kmh for infantry is fine as a realistic hourly rate, but 12 hours a day is a forced march pace that's not sustainable. In one test I marched a Russian division from Minsk to Moscow in the middle of winter and the average speed in game was above 3kmh - or more than 36 km a day. 2/3's that makes for a good sustainable march rate. As to speeds, there's also lots of units with Recon or Engineers which speeds things up.

Even where railways exist in isolation from any roads, the rails provide a route that's much easier than trying to go cross-country. For example in Burma the 17th Indian Division used the railway bridge over the Sittang River to drive trucks and move other equipment back to the west bank. Sure it wasn't as fast as driving them over a road bridge, but it was a hell of a lot faster than trying to construct rafts to carry them over. I'd argue that a 10 Infra state has very good rail and road networks - but I would actually prefer province based infrastructure as that gives the ability to better represent true bottlenecks such as tunnels through mountains. Then there's also the issue that it costs just as much to improve the infrastructure of Luxembourg as it does to improve the infrastructure in the northern half of Norway.