New MvtTileDecoder to allow parsing mvt pbf tiles

[boldtrn]

This PR adds a new MvtTileDecoder, using this nice project. The above mentioned project apparantly does not work with older Android version, that's why I used a fork (which will be hopefully merged soon) that supports older Android versions as well (the issue is that the project used some JDK8 methods, see here). I tried the new decoder with Mapzen and OMT, both basically work.

There is an issue with decoding Polygons. Probably I made a mistake when creating the new decoder or maybe the MvtReader does something odd? Maybe someone can have a look? I think there might be something messed up with holes and the outer shell, but I don't know what.

Screenshots from OMT:

Screenshots from Mapzen:

[boldtrn]

BTW I also received an issue when running:

./gradlew clean build

Execution failed for task ':vtm-android-example:transformDexArchiveWithExternalLibsDexMergerForDebug'.
> java.lang.RuntimeException: java.lang.RuntimeException: com.android.builder.dexing.DexArchiveMergerException: Unable to merge dex

[boldtrn]

BTW: An alternative library to use could be this one. I haven't compared them in detail, this library hasn't been updated since mid 2016, but has more stars. Both libraries are under Apache2 and use JTS at its core.

[boldtrn]

I did some more digging regarding the Polygon issue and saw that the reason is probably in the used library and create an issue.

[boldtrn]

Thanks to @ShibaBandit I was able to resolve the Polygon issue, the maps look perfect (or at least similar to our current geojson endpoint) now from what I can see. Performance feels good, didn't run any detailed performance comparisons.

OMT:

Mapzen:

[boldtrn]

I guess a good next step would be to move the new code into it's own package to avoid additional dependencies in the core?

[devemux86]

Thanks, will check it!

It's nice that there are still people willing to share work with the community. 🙂

[devemux86]

I guess a good next step would be to move the new code into it's own package to avoid additional dependencies in the core?

Definitely, vtm module should remain free from third-party dependencies.
I can do it while reviewing and before merging.

[boldtrn]

I can do it while reviewing and before merging.

Sure, please feel free to go ahead :)

[devemux86]

Execution failed for task ':vtm-android-example:transformDexArchiveWithExternalLibsDexMergerForDebug'.
> java.lang.RuntimeException: java.lang.RuntimeException: com.android.builder.dexing.DexArchiveMergerException: Unable to merge dex

That could be due to many vtm-android-example dependencies.
I had fixed that when Gradle 4 was instroduced via enabling minify, but latest Android plugin seemed to solve the situation and I reverted the change in 9b14865 to regain performance in debugging.
Will see with the PR new dependencies and if needed can enable again that fix.

[devemux86]

For Gradle build also to pass, better use here:

decoder.decode(tile, sink, getClass().getResourceAsStream("/mvt-test.pbf"));

I'll include it in merge.

[devemux86]

Thanks for the very nice work!
Merged via d049d37.

I introduced vtm-mvt module to host MVT tile decoder and sources.
The polygons fix requires the latest mapbox-vector-tile and so Android minSdkVersion 26, will see how can improve it after their changes.