Merge pull request #2981 from pavelmachek/m_8_spacew

Add Space Weaver -- vector map application.

apps/spacew/README.md

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+# Space Weaver ![](app.png)
+
+Vector map
+
+Written by: [Pavel Machek](https://github.com/pavelmachek)
+
+Space Weaver is application for displaying vector maps. It is
+currently suitable for developers, and more work is needed.
+
+Maps can be created from openstreetmap extracts. Those are cut using
+osmosis, then translated into geojson. Geojson is further processes to
+add metadata such as colors, and to split it into xyz tiles, while
+keeping geojson format. Tiles are then merged into single file, which
+can be uploaded to the filesystem. Index at the end provides locations
+of the tiles.
+
+## Preparing data
+
+Tools in spacew/prep can be used to prepare data.
+
+You'll need to edit prepare.sh to point it to suitable osm extract,
+and you'll need to select area of interest. Start experiments with
+small area. You may want to delete cstocs and provide custom
+conversion to ascii.
+
+Details of which features are visible at what zoom levels can be
+configured in split.js. This can greatly affect file sizes. Then
+there's "meta.max_zoom = 17" setting, reduce it if file is too big.
+
+For initial experiments, configure things so that mtar file is around
+500KB. (I had troubles with big files, both on hardware and to lesser
+extent on simulator. In particular, mtar seemed to be corrupted after
+emulator window was closed.)
+
+## Future Development
+
+Directories at the end of .mtar should be hashed, not linear searched.
+
+Geojson is not really suitable as it takes a lot of storage.
+
+It would be nice to support polygons.
+
+Web-based tool for preparing maps would be nice.