Calculate offline routes and distances with GraphHopper on the Android device using a native image of GraphHopper instead of the jar dependency.

It already works :) ! And performance is "okay". E.g. 300km route within 2 seconds on a OnePlus 5T device.

There are the following advantages:

• no per-process virtual memory limit (see current lower other memory problems)
• GraphHopper itself does not need to limit itself to Java 7
• this process here is the "Android Java" path but works also and much easier with Gluon and JavaFX
• same process could work for iOS too
• public transit could work too (currently requires Java 8 features)
• data import of raw OSM files (especially for small areas) could work too (i.e. on-demand areas and routes could be possible)

The main disadvantage is the complexity of the process: you not only need to build the graphhopper jar but the Android NDK & SDK and GraalVM and a maven plugin to create a native library that apps integrate via Android NDK and not 'directly'.

See also TODOs.

• Get the repository https://github.com/karussell/graphhopper-native-image/
• cd android
• mvn clean install
• download a pbf file from OSM e.g. wget http://download.geofabrik.de/europe/germany/berlin-latest.osm.pbf
• ln -s berlin-latest.osm.pbf osm.pbf
• java -jar target/graphhoppernative-1.0-SNAPSHOT-jar-with-dependencies.jar
• adb push graph-cache/ /data/local/tmp/

Follow instructions in https://github.com/karussell/graphhopper-native-image/#build-android

Copy the created libgraphhoppernative.so into distribution/ghlib/arm64-v8a/ of this repository here.

• Communication with library is unclear. Currently we can only send coordinates to it but cannot receive something (we can only read log messages). Maybe we start dropwizard on Android and communicate via the normal http client :) ?
• What other targets besides arm64-v8a can we support?
• Can we avoid app crashes when doing multiple route calculations (how is memory management done?)
• There are app crashes when doing longer routes (memory problems)