Limit annotation tiles to z16

[kkaefer]

We're currently generating annotation tiles all the way up to z22:

mapbox-gl-native/src/mbgl/annotation/render_annotation_source.cpp

Line 41 in 2166b85

{ 0, util::DEFAULT_MAX_ZOOM },

In most cases, however, it's unnecessary to regenerate the tiles for higher zoom levels. We should limit the tiles to z16 to match the tile level most vector tilesets use as well.

[1ec5]

What’s the implication of limiting the annotation tile zoom level? Just that point and shape annotation coordinates will be simplified to z16 and overzoomed after that, correct?

Would it be possible to dynamically match the maximum maxzoom of the current non-annotation sources?

[1ec5]

The maximum zoom level was increased to z22 in #5517. (I found it because we happened to mention it in the iOS SDK changelog, but I don’t know that any developer is terribly dependent on this behavior.)

[jfirebaugh]

I have the same questions as @1ec5.

[kkaefer]

Yeah, annotations will only exist up to z16, and we will overzoom tiles from there on. @GretaCB has a great explanation in https://github.com/mapbox/vector-tiles/issues/45#issuecomment-325781516 of why z16 is sufficient for those tiles.

Would it be possible to dynamically match the maximum maxzoom of the current non-annotation sources?
We could do that, but then we couldn't guarantee accuracy of annotations anymore. E.g. if you only have another source that uses 0-8, overzoom those tiles, then annotation tiles would also be limited to z8, which might produce precision issues.

We could, however, expose the maxzoom as a property for the annotations source, so that you could modify this at runtime.

[brunoabinader]

We could, however, expose the maxzoom as a property for the annotations source, so that you could modify this at runtime.

I think we'll get that already when refactoring annotations based on runtime styling.

[1ec5]

Mind adding something to the iOS and macOS changelogs about this fix?

[kkaefer]

Mind adding something to the iOS and macOS changelogs about this fix?

Technically, this is an internal change that shouldn't affect external behavior, so I'm hesitant to add a changelog item. We're not really exposing the concept of tiles in the context of annotations to the end user so far.