Determine shortest distance between point to a (small) path of OSM?

Question

When using offline on a mobile (Android) device: How can I calculate the shortest distances between any point and the nearest (small) OSM path?

The offline file with graph/routing data could be used by a library to do the distance calculating. The size could be for a country like the Netherlands.

What kind of paths? I mean especially the smallest paths, like footpaths, hiking trails, etc. I don't need any further routing facilities.

How will I use the data? About 6 years I do geocaching with my onw geocaching app. I use OsmDroid, OsmDroid-with-Mapsforge i.c.m. OsmBonuspack. I work with downloaded mapsforge-v5 downloaded maps.

I am building a lot of AI stuff in my app so that I can guesstimate locations when I can't figure them out. For the last piece of AI I need to determine the shortest distance between any point to the nearest (foot)path.

If offline is too difficult, is there any API that can be called?

An example: I have a series coordinates (or points) in the woods. Which point is nearest to a footpath?

UPDATE: a lot of useful info is found at this location. So, now I only need to use the unpacked and pre-processed stuff to use the detailed API. Anyone experience with a simple main() method that does the trick?

Answer 1

The following solution works:

• Get the graphhopper project in your IDE.
• Get the raw Openstreetmap data (.pbf) via this very nice provider.
• Run this command in your (git) bash shell: ./graphhopper.sh -a import -i gelderland-latest.osm.pbf. Of course, you take your own OSM area.
• Make a new (maven) project with this pom.xml file:

  <dependency>
    <groupId>nl.xyz</groupId>
    <artifactId>graphhopper</artifactId>
    <version>1.0</version>
    <scope>system</scope>
    <systemPath>${project.basedir}/libs/graphhopper-web-1.0-SNAPSHOT.jar</systemPath>
  </dependency>

• Copy generated graphhopper-web-1.0-SNAPSHOT.jar from the graphhopper project to the libs folder of your new project so it will be included in your path. It may be even better to use a Gradle/Maven dependency of the graphhopper core or web libraries.

• Copy the generated graphhopper data to a folder within your small project.

• Create this simple demo:

  public static void main(String[] args) {
      private static String mapsFolder = "graphhopper-data/yourlocation-latest.osm-gh";
      GraphHopper graphHopper = new GraphHopper().forMobile();
      graphHopper.load(mapsFolder);
      System.out.println("Found graph " + graphHopper.getGraphHopperStorage().toString() + ", nodes:" + graphHopper.getGraphHopperStorage().getNodes());
      QueryResult queryResult = graphHopper.getLocationIndex().findClosest( 52.11111, 6.111111, EdgeFilter.ALL_EDGES);
      double distance = queryResult.getQueryDistance();
      System.out.println( "Shortest distance is: " + distance);
  }
  

I hope you enjoy this wonderful 'graphhopper' software!

UPDATE: Using the JAR on Android may give a lot of compiler errors due to library version mismatchers. A better solution for getting this example run at Android, is using this dependency in your build.gradle:

implementation 'com.graphhopper:graphhopper-core:1.0-pre33'

Consequence is that you have to set the default routing profile. You can achieve via this change:

graphHopper = new GraphHopper().forMobile();
// Next line: 
graphHopper.setProfiles( Collections.singletonList(new ProfileConfig("my_car").setVehicle("car").setWeighting("fastest")));
graphHopper.load(routingDataFolder);