Work with prefetched OSM tiles from local SD

[Matthias Apitz]

It is relatively easy to prefetch tiles from the OSM servers and have them
as a local tree, for example on the SD like

OSM/10/0
OSM/10/0/0.png
OSM/10/0/1.png
OSM/10/1
OSM/10/1/0.png
OSM/10/1/1.png
OSM/10/272
OSM/10/272/445.png
OSM/10/272/446.png
OSM/10/273
OSM/10/273/384.png
...
OSM/18/139404
OSM/18/139404/90871.png
OSM/18/139404/90872.png
OSM/18/139404/90873.png

Of course, they need there space and one can not have world on the device, but at least
the areas of interest. I have two big cities, Munich and Havanna where I live or travel
and they need upto lavel 18 only 1 GByte of space.

uNav should use such "offline" tiles if they are there in preference of fetching them
from the OSM servers.

A possible solution we are testing at the moment is a modified unav.desktop
file as:

    Desktop Entry]
    Name=unav-osm
    Type=Application
    Exec=/usr/bin/nohup /home/phablet/unav.sh
    Icon=/userdata/system-data/opt/click.ubuntu.com/navigator.costales/0.57/icon.png
    Terminal=false
    X-Ubuntu-Touch=true

and launching in front of uNav a small HTTP server with the script /home/phablet/unav.sh
as:

    #!/bin/sh

    # 1st start the local HTTP server:
    cd /media/phablet/*/Maps
    python3 -m http.server 8888 &

    # now start uNav
    cd /userdata/system-data/opt/click.ubuntu.com/navigator.costales/0.57/
    qmlscene %u qml/Main.qml

This works very nicely with a modified /userdata/system-data/opt/click.ubuntu.com/navigator.costales/0.57/index.html
to direct the request to http://127.0.0.1:8888/osm/

Other solutions may be possible.

[costales (costales)]

Thanks a lot Matthias for your help ;)
You are a great hacker :)

[Nicolas DERIVE (kalon33)]

Maybe that would be great to investigate how OSMAnd does (https://github.com/osmandapp/Osmand), as it seems to use compressed xml files which are space savvy and is able to render maps locally.

It also deals with offline navigation, which would be a nice feature for uNav too.

[costales (costales)]

This will be possible when system allows that. Until now, upstream bug ;)