How To Use OSM Tiles Offline with uNav g...@unixarea.de
The problem The app for UbuntuTouch "uNav" works only with Internet connection when presenting maps and locations. Sometimes Internet is not reliable or over data mobile even expensive and the idea to workaround is having the maps' tiles prefetched and stored in the Ubuntu phone. Here is the tool chain so solve this. 1. Prefetching OSM tiles for a given area of interest and There is a C-written tool 'osmtiles' to be fetched an compiled on your Linux or FreeBSD workstation: http://www.millions.ca/~stacy/osmtiles.tgz Compilation is simple (see its README): ``` tar xzf osmtiles.tgz cd osmtiles cc -o osmtiles osmtiles.c -lm ``` The tool 'osmtiles' allows to make a list of all OSM tiles of a given GPS coordinates of an area, for example: ``` osmtiles -z 9 -Z 18 \ 23.178555 -82.462692 \ 23.050039 -82.288628 \ > havana.txt ``` The above region 23.178555 -82.462692 x 23.050039 -82.288628 is the capital of Cuba, Havana. The output of the tool is a list file like this: ``` 9/138/222.png 10/277/444.png 11/554/888.png 11/554/889.png 11/555/888.png 11/555/889.png 12/1109/1776.png ... ``` Some ~18.000 lines, i.e. tiles, to fetch. This list is stored for fetch (and later updates) in a file, let's say havana.txt. I have a bunch of such files for the places I visit. Based on this list I have a shell script which in principle does for any of the files in the list: ``` while read name ; do fetch the MD5 sum from the server for the file http://tile.openstreetmap.org/$name if the MD5 is different from what I have fetch the file http://tile.openstreetmap.org/$name done < havana.txt ``` This way, later on updates, only modified tiles will be fetched. I can share this script, no problem, if you promise not to blame me, but send patches for it. Next step is making, again based on the file of the place to visit, a tar archive: ``` cd osm tar --files-from=../Havana.lst -czf ../Havana.tgz ls -lh ../Havana.tgz -rw-r--r-- 1 guru wheel 93M 24 may. 16:58 ../Havana.tgz ``` i.e. such a file is around 100 MByte in size. Move these file(s) to the phone with SCP or ADB and unpack them on the SD card to some directory which will later be served by a small Python web server. 2. The modifications in the phone We start with copy over the file Havana.tgz to the phone and unpack it there: ``` scp -p Havana.tar.gz phablet@192.168.2.102:. ssh phablet@192.168.2.102 ls /media/phablet/ 9CC0-D6CE mkdir /media/phablet/9CC0-D6CE/Maps cd /media/phablet/9CC0-D6CE/Maps tar xzf ~/Havana.tar.gz ``` Note: the dir `9CC0-D6CE` may vary depending on the SD type. Change this to the name in your phone and later in the start script for the Python web server too. Unpacking the tar archive should give: ``` ls /media/phablet/9CC0-D6CE/Maps/ osm ls /media/phablet/9CC0-D6CE/Maps/osm 10 11 12 13 14 15 16 17 18 9 ``` i.e. the tiles in their sub-dirs `9 ... 18`. To start our special `uNav-osm` app we need a new desktop entry as `~/.local/share/applications/unav-osm.desktop` which must contain the following lines: ``` [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/current/icon.png Terminal=false X-Ubuntu-Touch=true ``` As you see it will not execute the `uNav` app directly, but a small shell script `/home/phablet/unav.sh`. This script starts upfront the Python web service and then the `uNav` app itself. It has the folling few lines. ``` #!/bin/sh # cd /media/phablet/9CC0-D6CE/Maps python3 -m http.server 8888 & # cd /userdata/system-data/opt/click.ubuntu.com/navigator.costales/current qmlscene %u qml/Main.qml > /dev/null 2> /dev/null ``` Create this script `/home/phablet/unav.sh` with `vi` and make it executable: ``` vi /home/phablet/unav.sh chmod 0755 /home/phablet/unav.sh ``` Last action is to make a small modification in `uNav` itself. At the time of writing it is the version 2.3 and the fix must be done in this file: `/userdata/system-data/opt/click.ubuntu.com/navigator.costales/current/nav/index.html` What to change is best visible in this diff: ``` cd /userdata/system-data/opt/click.ubuntu.com/navigator.costales/current/nav diff index.html index.html.orig 210c210 < source: new ol.source.OSM({url: 'http://localhost:8888/osm/{z}/{x}/{y}.png'}), --- > source: new ol.source.OSM({url: > 'http://{a-c}.basemaps.cartocdn.com/rastertiles/voyager/{z}/{x}/{y}.png'}), ``` The file must be modified as root and it's a good idea to make a copy (like I did): ``` sudo su cd /userdata/system-data/opt/click.ubuntu.com/navigator.costales/current/nav cp -p index.html index.html.orig vi index.html ``` Note: the URL `http://{a-c}.basemaps.cartocdn.com/rastertiles/...` appears three times in the file. Change only the first location for `/voyager/....` because this is also what you want to pick-up in the `Settings` menu of `uNav` for the value: ``` Mode Online Online style Carto Voyager <--------------- ``` That's it as changes. One final note: You have only offline tiles for small places and not the world between. So, you can't slide over the world, for example from Munich to Havana. If you leave your location of offline tiles you will see only a white map in `uNav`. The way to move is configure in `Settings` some other `Online style`, for example `Mapbox`. Or configure locations as `Favourites` to jump over the Ocean. -- Matthias Apitz, ✉ g...@unixarea.de, http://www.unixarea.de/ +49-176-38902045 Public GnuPG key: http://www.unixarea.de/key.pub May, 9: Спаси́бо освободители! 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