Mapsforge map artifacts for extraction zoom >17

[devemux86]

When we use a Mapsforge map with max rendering zoom >17, like new MapFileTileSource(0, 18), we have artifacts at tile grid lines.

[devemux86]

Related to opensciencemap#122 and opensciencemap#123

Blocks #216

[devemux86]

After @hjanetzek 's comment, possible cause seems being the TileClipper used in MapDatabase.

Wondering what's its benefit specifically for Mapsforge maps.
Also at next line we have additional map element simplification.

[devemux86]

@andreynovikov can you test all these also from your side?

[devemux86]

I changed TileClipper buffer to half the tile size, like most tile buffers.
Nicely also described in TileMill Metatiles, hoping it isn't too much. 🙂

Rendering in zoom >17 with new MapFileTileSource(0, 18) seems fine now, need good testing by all.

[devemux86]

There are still artifacts (1) at very large zooms >20 and elements disappear (2) if most of tile is outside screen, both with new MapFileTileSource(0, 18).

Artifacts:

Disappearance:

[devemux86]

Having half tile size as TileClipper buffer seems not excellent for performance.. 🙁

[devemux86]

I changed TileClipper buffer to be scaled on dpi.

[andreynovikov]

Sorry, didn't catch, what should I test?

[devemux86]

@andreynovikov do you use MapFileTileSource with default max zoom or >17 and see any artifacts?

I wonder of the purpose of tile clipping here and improved it to have a scaled buffer.

And in next line we have a simplify call, seems a bit redundant in Mapsforge maps?

[devemux86]

In Mapsforge we had added extra checks in processPOIs and processWays for including only the elements in the requested tiles.

[andreynovikov]

No, I use default and do not have such issues.

[devemux86]

Large query zoom levels have also polygon artifacts as reported in #391.

The buildings cause that issue (as seen in urban areas), e.g. disabling them in the theme eliminates any artifacts.

Reason is in MapDatabase.processWays there is a check to not use TileClipper for buildings, probably due to opensciencemap#124.

[devemux86]

Pushed in MapDatabase at large query zoom levels:

• Clip everything (also buildings)
• Use enlarged clip buffer