How to prevent graphhopper from finding a route that it can't take

wuan580 · August 25, 2022, 8:30am

Hi everyone,
I’m facing a situation where graphhopper’s algorithm chooses to take the waterway, but in reality you want to take that route so you have to start from a far away stop. Is there a way to configure the algorithm so that the algorithm does not choose that waterway but chooses the road?
Current:

And I want it like this:

Thank you so much!

karussell · August 25, 2022, 8:51am

Yes, you can specify “snap_preventions”:[“ferry”] (or snap_prevention=ferry for the GET request) to avoid this:

github.com

graphhopper/graphhopper/blob/master/docs/web/api-doc.md#parameters

## Routing Web API Docs

In order to communicate with your or [our](http://graphhopper.com/#enterprise) hosted GraphHopper 
server you need to understand how to use it. There is a separate [JavaScript](https://github.com/graphhopper/directions-api-js-client) and [Java](https://github.com/graphhopper/directions-api-java-client) client for this API or use the plain JSON response for your language.
To find out how to use the hosted GraphHopper Directions API you should refer to the online documentation [here](https://docs.graphhopper.com/). This file describes the web API of the open source routing server.

### A simple example
[http://localhost:8989/route?point=52.5300591%2C13.3565022&point=52.5060440%2C13.4378107](http://localhost:8989/route?point=52.5300591%2C13.3565022&point=52.5060440%2C13.4378107)

The URL path of the local instance is [http://localhost:8989](http://localhost:8989)

The endpoint to obtain the route is `/route` via GET.

## HTTP POST

The GET request has an URL length limitation, so it won't work for many locations per request. In those cases use a HTTP POST request with JSON data as input. The POST request is identical except that all singular parameter names are named as their plural for a POST request. All effected parameters are: `points`, `snap_preventions`, `curbsides` and `point_hints`. (`details` stays `details`)

Please note that unlike to the GET endpoint, points are specified in `[longitude, latitude]` order. For example `point=10,11&point=20,22` will be the following JSON:

```json

This file has been truncated. show original

wuan580 · August 25, 2022, 9:01am

Can you explain in more detail? As I understand, this config will make the algorithm skip the route search with type ferry. How can I configure the POST api?

Many thanks,

otbutz · August 25, 2022, 9:08am

Snapping refers to the selection of start/end points. Your routing happens to select the ferry route as a startpoint. From there it can only follow it which yields this “strange” route.

karussell · August 25, 2022, 9:16am

Snapping refers to the selection of start/end points. Your routing happens to select the ferry route as a startpoint. From there it can only follow it which yields this “strange” route.

As I wrote: "snap_preventions":["ferry"]

wuan580 · August 25, 2022, 9:17am

Can I configure it in the config file?

karussell · August 25, 2022, 9:35am

No, this is not possible.

What you could do is the exclude ferries for routing in general using a custom profile: https://github.com/graphhopper/graphhopper/blob/master/docs/core/profiles.md#custom-profiles

using the following custom_model:

{
 "priority": [{
   "if": "road_environment == FERRY",
   "multiply_by": "0.0"
 }]
}

You can copy and paste this custom_model directly in the config.yml like this (make sure the starting bracket is on the line of the custom_model):

profiles:
  - name: my_custom_profile
    vehicle: car
    weighting: custom
    custom_model: {
     "priority": [{
       "if": "road_environment == FERRY",
       "multiply_by": "0.0"
     }]
    }

or the “pure” yml:

profiles:
  - name: my_custom_profile
    vehicle: car
    weighting: custom
    custom_model:
     priority:
       - "if": "road_environment == FERRY"
         "multiply_by": "0.0"

system · November 23, 2022, 9:36am

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