[OSRM-talk] Need help: Customizing weights in Profile shows inconsistent results with Dijsktra

[Niharika Shrivastava]

Hello, I'm new to OSRM and I went through previous issues and couldn't find
much related to this, hence posting it here.

I had used a python library OSMnx to extract Singapore's data and changed
certain edge attributes for it. I calculated an edge attribute `"BPR"`
(float) and stored it in the graph (This is travel time in case of real
traffic data). I then converted this modified graph into a shapefile and
then converted the shapefile into OSM XML using JOSM. I fed this to OSRM in
order to use CH. I want to find the shortest route between two points
wherein my weights (or cost) are the BPR value I had calculated. I
understand I have to specify that in the car profile. This is how I
specified it:

```
function setup()
  return {
    properties = {
      ...
      weight_name     = 'congestion',
      ...
    },
  ...
}


function process_way(profile, way, result, relations)
  local data = {
    -- prefetch tags
    ...
    BPR = way:get_value_by_key('BPR')
  }

  result.weight = data.BPR
  ...
}
```

This is the JSON response I get for a certain query:
```
{'code': 'Ok',
 'routes': [{'geometry': 's}gG{ijyReEnNdm@|Wpl@~}@b\\lfAw\\twAbFjt at wM
`ZwSpAGnNgN|Dvm at fWwHhb@bErz at qFxeAzVfkAfr@b{Ak_ at rr@ocA~dAgCda at ji@dz@`j at di
@`Sfi at PfQcRpc@ySyCgw@~XjEx]dHDkEl\\ju at lf@ii at n}@oVqEiKlR_Elw at bJd[lc at wFdKf[',
   'legs': [{'steps': [],
     'distance': 32298.2,
     'duration': 2308.4,
     'summary': '',
     'weight': 2179.6}],
   'distance': 32298.2,
   'duration': 2308.4,
   'weight_name': 'congestion',
   'weight': 2179.6}],
 'waypoints': [{'hint':
'YwYBgG8GAYALAAAAAQAAAAAAAAAAAAAAHN-XQWpx4j0AAAAAAAAAAA0AAAABAAAAAAAAAAAAAAAJAAAAyOIxBiSzFADI4jEGJLMUAAAAzwFqJcKJ',
   'distance': 0,
   'name': 'Tampines Avenue 8',
   'location': [103.932616, 1.35658]},
  {'hint':
'EAYBgBcGAYAUAAAAAAAAAAAAAAAAAAAAPzfZQQAAAAAAAAAAAAAAABkAAAAAAAAAAAAAAAAAAAAJAAAA6oIuBlR3FADqgi4GVHcUAAAALwpqJcKJ',
   'distance': 0,
   'name': 'Boon Lay Drive',
   'location': [103.711466, 1.341268]}]}
```

Looking at this part from the JSON:
 ```
 'duration': 2308.4,
  'weight': 2179.6}],
```
As I understand, weight is the summation of BPR values for each edge.
Duration is estimated free flow time:` length/max_speed for each edge`. The
`value of weight should be >= duration` which is true when I use Dijkstra
for routing using edge weights as BPR value (`3155.27`). But over here,
thats not the case.

BPR = duration*(some delay based on traffic) >= duration in case of no
traffic

Can someone please point out if my Profile is wrongly written or if I've
missed any steps?
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