Brute-force ballistic calculator

ballistic_calculator.lua

---
--- Original creator of formulas: @sashafiesta on Discord
--- Original creator of python adaptation: @malexy on Discord
--- Optimized and translated python code to lua: SpaceEye. (https://gist.github.com/SuperSpaceEye/c33443213605d1bf35f81737c9058dc2)
--- Some lua optimizations: Autist69420
---

-- Simple micro-optimizations for better performance
local table_insert = table.insert
local rad, sin, cos, log, abs, min, pow = math.rad, math.sin, math.cos, math.log, math.abs, math.min, math.pow
local tu = table.unpack

local function linspace(start, end_, num)
    local linspaced = {}
    if num == 0 then return linspaced end
    if num == 1 then
        table_insert(linspaced, start)
        return linspaced
    end

    local delta = (end_ - start) / (num - 1)

    for i = 0, num-2 do
        table_insert(linspaced, start+delta*i)
    end
    table_insert(linspaced, end_)

    return linspaced
end

local function range(start, stop, step)
    step = step or 1
    local pos = start
    return function ()
        if step > 0 then
            if pos >= stop then return nil end
        else
            if pos <= stop then return nil end
        end
        local lpos = pos
        pos = pos + step
        return lpos
        end
end

local function flinspace(start, stop, num_elements, min, max)
    local items = linspace(math.max(start, min), math.min(stop, max), num_elements)
    local pos = 0
    return function() -- simple iterator
        pos = pos + 1
        return items[pos]
    end
end

local function get_root(d, from_end)
    if from_end then
        for i = #d-1, 1, -1 do
            if d[i][1] > d[i+1][1] then return d[i+1] end
        end
        return d[1]
    else
        for i = 2, #d, 1 do
            if d[i-1][1] < d[i][1] then return d[i-1] end
        end
        return d[#d]
    end
end

local function time_in_air(y0, y, Vy, gravity, max_steps)
    local t = 0
    local t_below = 9999999

    gravity = gravity or 0.05
    max_steps = max_steps or 1000000

    if y0 <= y then
        local y0p
        while t < max_steps do
            y0p = y0
            y0 = y0 + Vy
            Vy = 0.99 * Vy - gravity
            t = t + 1

            if y0 > y then
                t_below = t-1
                break
            end

            if y0 - y0p < 0 then
                return -1, -1
            end
        end
    end

    while t < max_steps do
        y0 = y0 + Vy
        Vy = 0.99 * Vy - gravity
        t = t + 1

        if y0 <= y then return t_below, t end
    end

    return t_below, -1
end

local function get_min(array)
    local min_delta_t = array[1][1]
    local pitch_ = 0;
    local airtime_ = 0;
    for i = 1, #array do
        if min_delta_t > array[i][1] then
            min_delta_t  = array[i][1]
            pitch_ = array[i][2]
            airtime_ = array[i][3]
        end
    end
    return min_delta_t, pitch_, airtime_
end

local function try_pitch(tried_pitch, initial_speed,
                         length, distance, cannon, target, gravity, max_steps)
    gravity = gravity or 0.05
    max_steps = max_steps or 1000000

    local tp_rad = rad(tried_pitch)

    local Vw = cos(tp_rad) * initial_speed
    local Vy = sin(tp_rad) * initial_speed

    local x_coord_2d = length * cos(tp_rad)

    if Vw == 0 then return nil, false end
    local part = 1 - (distance - x_coord_2d) / (100 * Vw)
    if part <= 0 then return nil, false end
    local horizontal_time_to_target = abs(log(part) / (-0.010050335853501))

    local y_coord_of_end_barrel = cannon[2] + sin(tp_rad) * length

    local t_below, t_above = time_in_air(y_coord_of_end_barrel, target[2], Vy, gravity, max_steps)

    if t_below < 0 then return nil, false end

    local delta_t = min(
            abs(horizontal_time_to_target - t_below),
            abs(horizontal_time_to_target - t_above)
    )

    return {delta_t, tried_pitch, delta_t + horizontal_time_to_target}, true
end

local function try_pitches(iter, ...)
    local delta_times = {}
    for pitch in iter do
        local items, is_successful = try_pitch(pitch, ...)
        if is_successful then table.insert(delta_times, items) end
    end
    return delta_times
end

-- Required parameters:
-- cannon = table of three numbers: x, y, z of cannon
-- target = same as cannon but for target
-- initial_speed = speed in m/s
-- length = length of a cannon
-- Optional parameters:
-- max_steps = maximum number of steps program will simulate projectile before declaring it unreachable
-- max_delta_t_error = maximum difference between horizontal and vertical times to target before declaring target impossible to hit. Only matters if check_impossible is enabled
-- amin = minimum cannon angle
-- amax = maximum cannon angle
-- gravity = x m/tick
-- num_iterations = number of refining steps after roughly calculating angle
-- num_elements = number of elements to test during refining stage
-- check_impossible = does additional check for targets that are impossible to hit
local function calculate_pitch(cannon, target, initial_speed, length,
                               optional)
    local max_steps, max_delta_t_error, amin, amax, gravity, num_iterations, num_elements, check_impossible
    optional = optional or {}
    max_steps = optional.max_steps or optional[1] or 100000
    max_delta_t_error = optional.max_delta_t_error or optional[2] or 1
    amin = optional.amin or optional[3] or -30
    amax = optional.amax or optional[4] or 60
    gravity = optional.gravity or optional[5] or 0.05
    num_iterations = optional.num_iterations or optional[6] or 5
    num_elements = optional.num_elements or optional[7] or 20
    check_impossible = optional.check_impossible or optional[8] or true

    local Dx, Dz = cannon[1] - target[1], cannon[3] - target[3]
    local distance = math.sqrt(Dx * Dx + Dz * Dz)

    local delta_times = try_pitches(range(amax, amin-1, -1), initial_speed, length, distance, cannon, target, gravity, max_steps)
    if #delta_times == 0 then return {-1, -1, -1}, {-1, -1, -1} end

    local dT1, p1, at1 = tu(get_root(delta_times, false))
    local dT2, p2, at2 = tu(get_root(delta_times, true))

    local c1 = true
    local c2 = not p1 == p2
    local same_res = p1 == p2

    local dTs1, dTs2

    for i in range(0, num_iterations) do
        if c1 then dTs1 = try_pitches(flinspace(p1-pow(10,-i), p1+pow(10,-i), num_elements, amin, amax), initial_speed, length, distance, cannon, target, gravity, max_steps) end
        if c2 then dTs2 = try_pitches(flinspace(p2-pow(10,-i), p2+pow(10,-i), num_elements, amin, amax), initial_speed, length, distance, cannon, target, gravity, max_steps) end

        if c1 and #dTs1 == 0 then c1=false end
        if c2 and #dTs2 == 0 then c2=false end

        if not c1 and not c2 then return {-1, -1, -1}, {-1, -1, -1} end

        if c1 then dT1, p1, at1 = get_min(dTs1) end
        if c2 then dT2, p2, at2 = get_min(dTs2) end
    end

    if same_res then dT2, p2, at2 = dT1, p1, at1 end

    local r1, r2 = {dT1, p1, at1}, {dT2, p2, at2}
    if check_impossible and dT1 > max_delta_t_error then r1 = {-1, -1, -1} end
    if check_impossible and dT2 > max_delta_t_error then r2 = {-1, -1, -1} end

    return r1, r2
end

local function calculate_yaw(Dx, Dz, direction)
    local yaw
    if Dx ~= 0 then
        yaw = math.atan(Dz/Dx) * 180/math.pi
    else
        yaw = 90
    end

    if Dx >= 0 then
        yaw = yaw + 180
    end

    local dirs = {90, 180, 270, 0}
    return (yaw + dirs[direction]) % 360
end

local function ballistics_to_target(cannon, target, power, direction, R1, R2, length)
    local directions = {north=1, west=2, south=3, east=4}
    direction = directions[direction]
    if direction == nil then error("Invalid direction") end

    local Dx, Dz = cannon[1] - target[1], cannon[3] - target[3]

    local r1, r2 = calculate_pitch(cannon, target, power, length)
    local yaw = calculate_yaw(Dx, Dz, direction)

    local rt = {}
    rt.yaw = yaw
    rt.yaw_time = yaw * 20 / (0.75 * R1)

    for k, v in pairs({[1]=r1, [2]=r2}) do
        local t = {pitch=-1, pitch_time=-1, airtime=-1, fuze_time=-1}
        if v[1] ~= -1 then
            t.delta_t = v[1]
            t.pitch = v[2]
            t.airtime = v[3]
            t.pitch_time = t.pitch * 20 / (0.75 * R2)
            t.precision = 1 - t.delta_t / t.airtime
        end
        table.insert(rt, k, t)
    end

    return rt
end

print("For the cannon coordinates, please input the coordinates of the cannon mount.")

cannonCoord = {}
print("x coord of cannon : ")
table_insert(cannonCoord, tonumber(io.read()))
print("y coord of cannon : ")
table_insert(cannonCoord, tonumber(io.read())+2)
print("z coord of cannon : ")
table_insert(cannonCoord, tonumber(io.read()))


targetCoord = {}
print("x coord of target : ")
table_insert(targetCoord, tonumber(io.read()))
print("y coord of target : ")
table_insert(targetCoord, tonumber(io.read()))
print("z coord of target : ")
table_insert(targetCoord, tonumber(io.read()))

print("Number of powder charges (int) : ")
powderCharges = tonumber(io.read())

print("What is the standart direction of the cannon ? (north, south, east, west)")
directionOfCannon = io.read()

print("What is the RPM of the yaw axis ?")
yawRPM = tonumber(io.read())
print("What is the RPM of the pitch axis ?")
pitchRPM = tonumber(io.read())

print("What is the length of the cannon ? (From the block held by the mount to the tip of the cannon, the held block excluded) ")
cannonLength = tonumber(io.read())

-- local cannonCoord = {323, 73+2, 32}
-- local targetCoord = {350, 84, -113}
-- local powderCharges = 8
-- local directionOfCannon = "north"
-- local yawRPM = 1
-- local pitchRPM = 1
-- local cannonLength = 31


local rt = ballistics_to_target(
    cannonCoord,
    targetCoord,
    powderCharges,
    directionOfCannon,
    yawRPM,
    pitchRPM,
    cannonLength
)

print("Yaw is ", rt.yaw)
print("With the yaw axis set at ", yawRPM, " rpm, the cannon must take ", rt.yaw_time, " ticks of turning the yaw axis.")

if rt[1].pitch ~= -1 then
    print("\nHigh shot:")
    print("Pitch is ", rt[1].pitch)
    print("Airtime is", rt[1].airtime, "ticks")
    print("With the pitch axis set at ", pitchRPM, " rpm, the cannon must take ", rt[1].pitch_time, " ticks of turning the pitch axis.")
    print("Precision: ", rt[1].precision)
else
    print("\nHigh shot is impossible")
end

if rt[2].pitch ~= -1 then
    print("\nLow shot:")
    print("Pitch is ", rt[2].pitch)
    print("Airtime is", rt[2].airtime, "ticks")
    print("With the pitch axis set at ", pitchRPM, " rpm, the cannon must take ", rt[2].pitch_time, " ticks of turning the pitch axis.")
    print("Precision: ", rt[2].precision)
else
    print("\nLow shot is impossible")
end

wait, @WOSAJ it's not t.airtime[1] but just t.airtime

i tried to fix this bug (it was cringe)

this error is more correct

@WOSAJ again, i do not have this error. So try copying the code again from gist

wait

okay, if you tried to execute your code with the parameters I specified and you don't have an error, the problem is on my side

damn, i see the issue

@WOSAJ i forgot that lua doesn't do table destructuring. Now it should be correct.

now it works very bad (the target is close, but for some reason it says that it is impossible, although it is a very simple shot)

@WOSAJ for very close targets you'll need to disable check_impossible

Technically you don't even need it, as long as you make logic for processing shots with low precision yourself

thanks