vminmax_simple.lua

--------------------------------------------
-- vminmax_simple: simple window based VMin and VMax signal.
--
-- OUT
-- channel: VMin
-- channel: VMax
--
-- IN
-- Speed
--

-- window size in seconds to keep track of first and last value.
local WINDOW_SIZE_SEC = 5
-- how many per seconds to record
local FREQUENCY = 10
-- minimum difference between edges and mid value to be considered a local value.
local MIN_DELTA_MPH = 10

-- name, Hz, precision, min, max, units
local minId = addChannel('VMin', 5, 0, 0, 200, 'mph')
local maxId = addChannel('VMax', 5, 0, 0, 200, 'mph')

-- recorded values
local vs = {}

-- local min/max calculation.
-- Returns signalId and value to update it to.
function __vminmax_signal()
  verbose(table.concat(vs, ','))
  local first, mid, last = vs[1], vs[math.ceil(#vs/2)], vs[#vs]
  verbose('first='..first..', mid='..mid..', last='..last..' @'..tick)
  -- too flat?
  if math.abs(mid-first) < MIN_DELTA_MPH or math.abs(mid-last) < MIN_DELTA_MPH then
    verbose('  too similar.')
    return 0, nil
  end
  -- maxima?
  if first < mid and last < mid then
    info('  new max='..mid)
    return maxId, mid
  end
  -- minima?
  if first > mid and last > mid then
    info('  new min='..mid)
    return minId, mid
  end
  verbose('  no hill.')
  return 0, nil
end

function tick_vminmax_simple()
  local speed = getChannel('Speed')
  if speed ~= nil and should_run(FREQUENCY) then
    -- append, resize, update.
    table.insert(vs, speed)
    if #vs > WINDOW_SIZE_SEC*FREQUENCY then table.remove(vs, 1) end
    if #vs == WINDOW_SIZE_SEC*FREQUENCY then
      local id, value = __vminmax_signal()
      if id ~= 0 then
        setChannel(id, value)
      end
    end
  end
end