Forwardmost Entity of a Train (Train direction)

[ssilk]

How can I know which is the forwardmost entity of a train?

Better explained: There is a front- and a back_stock. Which returns the first and last entity of a train. But how do I know, which one is now driving into front?
Differently explained: When a train is driving, the front gets blue lights, the back gets red lights. I want to know, which carriage is currently the front and which the back.

[Perhaps some function like train_direction(locomotive)
and it returns either 1 or -1 for currently driving into front or back-direction of train, so that I know if -1 then I need to pickup the back_stock for the forwardmost entity....]

PS: Also interesting: Which is the forwardmost locomotive?

[aubergine18]

proximity to front_rail or front_stock? http://lua-api.factorio.com/latest/LuaT ... l#LuaTrain

[ssilk]

No, depended to current driving direction.
The train doesn't change it's front and back, I tested that. it keeps the same, no matter in which direction I drive or in which cart I enter or if in automatic or manual mode.

Code: Select all

/c game.player.print("FRONT STOCK" .. game.player.selected.train.front_stock.unit_number);
game.player.print("BACK STOCK" ..game.player.selected.train.back_stock.unit_number);
for i, loco in pairs(game.player.selected.train.locomotives.front_movers) do
	game.player.print("Front Mover " .. i .. " . " .. loco.unit_number)
end
for i, loco in pairs(game.player.selected.train.locomotives.back_movers) do
	game.player.print("Back Mover " .. i .. " . " .. loco.unit_number)
end
for i, carr in pairs(game.player.selected.train.carriages) do
	game.player.print("Carr " .. i .. " . " .. carr.unit_number)
end

I made some edits to the post, perhaps you might read it again.

[Choumiko]

LuaTrain.speed is negative when the train moves in it's back direction, so something like

Code: Select all

/c game.player.print(game.player.selected.train.speed < 0 and game.player.selected.train.back_stock.unit_number or game.player.selected.train.front_stock.unit_number)

should give you the unit_number of the correct stock.

Forwardmost locomotive is either LuaTrain.locomotives.front_movers[1] or back_movers[1]

[ssilk]

Ahhh.... the speed! Of course....

[aubergine18]

But then what happens when it's stopped at station or signal?

[ssilk]

Well, as I understand it yet:
- A train has a train-direction, no matter, if it is running or not. Or differently explained: we need to begin with counting at the front of train.
- This direction doesn't change over time. Never. Front keeps front.
- Now you can drive the train in one of two directions: Same direction as train direction: Speed is positive. Opposite direction: Speed is negative.
- When the speed is 0, the direction is the direction of the train. Zero is in this case positive.

[aubergine18]

I imagine also that in arrays of locos or cargo, the numeric index will be in correct order also - so 1 = first (original front) loco or cargo array.

[ssilk]

Yes, AFAIK the order never changes. What changes is how you need to iterate them.

IMHO what is really missing: a flag what is was the last/is the current direction, in which the train has been/is driving? That would enable to find out the "right" direction, even if the train currently is standing still.

[mrvn]

What about if you have two locomotives?

The automatic trains never go backward so to go back and forth without turning you add 2 locomotives facing the opposite way so one always goes forward. Now does it actually go forward or does it go backward (speed negative) when it switches to the other locomotive?

[ssilk]

Tested and no: the train keeps the direction and order.

[Optera]

I can't believe this is not yet fixed.....
There's no sane way (measuring negative train speed is quite insane when you need orientation of a stationary train) through the API to determine which way a train faces.

[dgnuff]

Part of the problem is that it's completely ambiguous which is the front and which is the back if it's a double headed train stopped on a track that permits two way traffic.

That said, a couple of heuristics that can help:

1. If the train is on a one way track, then the front is possible to determine. I'm just not sure how we can do this from a mod, if at all.
2. A train can't be stopped at two stations at the same time, even if they're placed correctly to enclose a double headed train. Therefore when stopped at a station it's always possible to figure which is the front.

For point #2, we can do that ourselves now. If the train is stopped at a station, get the position of the front_stock, the back_stock and the station. Whichever of front_stock and back_stock is closest to to the station is the real front.

[Optera]

Part of the problem is that it's completely ambiguous which is the front and which is the back if it's a double headed train stopped on a track that permits two way traffic.

That said, a couple of heuristics that can help:

1. If the train is on a one way track, then the front is possible to determine. I'm just not sure how we can do this from a mod, if at all.
2. A train can't be stopped at two stations at the same time, even if they're placed correctly to enclose a double headed train. Therefore when stopped at a station it's always possible to figure which is the front.

For point #2, we can do that ourselves now. If the train is stopped at a station, get the position of the front_stock, the back_stock and the station. Whichever of front_stock and back_stock is closest to to the station is the real front.

It's only ambiguous when a train is stopped in manual mode or can't find a path.

Driving:
Front should be pretty obvious, it's just not available through the api and we have to do weird things like check for negative speed.

Stopped at signal:
Internally the game keeps track of the driving direction. Again it's just not available through the api.

Stopped in station:
As you said, the side closest to the stop is front.

I made a request for the api having a flag for these situations: viewtopic.php?f=28&t=43418