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tangrams / tangram

WebGL map rendering engine for creative cartography
https://tangram.city
MIT License
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make preserve_tiles_within_zoom an option in tile source config #758

Closed bdon closed 4 years ago

bdon commented 4 years ago

I didn't see anywhere preserve_tiles_within_zoom was being set other than to 0 for raster layers. Is the intention that this can be customized through the YAML? This PR adds it as an option in the YAML like so:

sources:
    tilezen:
        type: MVT
        url: https://tile.nextzen.org/tilezen/vector/v1/512/all/{z}/{x}/{y}.mvt
        tile_size: 512
        preserve_tiles_within_zoom: 4
bcamper commented 4 years ago

It's been an internal setting, but I don't mind exposing it as an option. The name has always been a bit awkward, so if we're going to make it public... have any suggestions for a simpler one? :) If not we'll keep as is.

Re: the behavior you mentioned seeing: with the default value of 1, I think the expected behavior is that this already should retain any tiles that are a full zoom level in/out from current view, and only prune those 2 or more levels out. Are you seeing cases where that doesn't seem to be true? If so we should also investigate. The main reason to not set this value higher is that it can theoretically retain a lot of tiles... but I suppose if the rest of the view pruning is working, it should stay manageable.

This also reminds me, @burritojustice has also wanted an option to control the view.buffer, which can be expanded to preload more tiles around the view area. That could be a follow-up to this.

bcamper commented 4 years ago

@bdon what are your current thoughts on exposing this publicly, given your most recent gitter comments?

bdon commented 4 years ago

Yeah, this can be closed as I'd rather investigate making some changes to TileManager.