example of a elevation based speed function using elevation-profile d…

…emo service

profiles/elevation.lua

@@ -0,0 +1,103 @@
+#!/usr/bin/lua
+-- example of a elevation based speed function using elevation-profile demo service
+require("curl")
+require("json")
+c = curl.easy_init() 
+
+function map(func, array)
+  local new_array = {}
+  for i,v in ipairs(array) do
+    new_array[i] = func(v)
+  end
+  return new_array
+end
+
+function params(pl,dist)
+  return 'path='..table.concat(map(function(x) return table.concat(x,",") end, pl),"|")..'&upsample='..dist..'&format=sjs'
+end
+
+-- input: 2d polyline
+-- output: upsampled 4d polyline with elevation and wgs84-distance from startpoint as 3rd and 4th dimension added
+function upsample_pl4d(pl,dist)
+   local header = {}
+   local body = {}
+   -- todo: maybe use http post
+   print('http://karme.de/elevation-profile/demo?'..params(pl,dist))
+   c:setopt(curl.OPT_URL,'http://karme.de/elevation-profile/demo?'..params(pl,dist))
+   c:setopt(curl.OPT_HEADERFUNCTION,function(s,len) table.insert(header,s) return len,nil end)
+   c:setopt(curl.OPT_WRITEFUNCTION,function(s,len) table.insert(body,s) return len,nil end)
+   c:perform()
+   local r=json.decode(table.concat(body))
+   assert(r['status']=='OK')
+   return r['results']
+end
+
+-- input: 4d polyline
+-- output: distance/elevation deltas
+function dz(pl)
+   local r={}
+   for i=1,table.maxn(pl)-1 do
+      r[i]={pl[i+1][4]-pl[i][4],pl[i+1][3]-pl[i][3]}
+   end
+   return r
+end
+
+-- input: delta
+-- output: gradient
+function gradient(x)
+   return x[2]/x[1]
+end
+
+-- simple speed function depending on gradient
+-- input: gradient
+-- output: speed
+function speed(g)
+   if g>0 then
+      return math.max(3,15-100*g)
+   else
+      return math.min(50,15-50*g)
+   end
+end
+
+function last(t)
+   return t[table.maxn(t)]
+end
+
+-- input: pl
+-- output: average speed
+function avg_speed(pl)
+   local pl4d=upsample_pl4d(pl,50)
+   local l=last(pl4d)[4]
+   --print(table.concat(map(table.concat,pl4d)))
+   local dzs=dz(pl4d)
+   --print(table.concat(map(table.concat,dzs)))
+   local speeds=map(speed, map(function(x) return x[2]/x[1] end, dzs))
+   --print(table.concat(speeds," "))
+   local time=0
+   for i=1,table.maxn(speeds) do
+      time=time+dzs[i][1]/speeds[i]
+   end
+   return l/time
+end
+
+-- todo
+function reverse(a)
+   local r={}
+   local n=table.maxn(a)
+   for i=1,n do
+      r[n-i+1]=a[i]
+   end
+   return r
+end
+
+function avg_speed_fwdbwd(pl)
+   return {avg_speed(pl),avg_speed(reverse(pl))}
+end
+
+function test(from,to)
+   print(table.concat(avg_speed_fwdbwd({from,to})," "))
+end
+
+test({48.5,9},{48.5,9.1})
+test({0,0},{0,0.1})
+test({48.52748,9.15578},{48.52408,9.14444})