[FEATURE] Tile underzooming (display tiles of larger zoom level at a smaller zoom level on the map)

[loaiz1982]

Feature Description

No native underzooming - Cannot display zoom 17 tiles at zoom 15.5

Sample Use Case

I have a raster.pmtiles file that has only zoom level 17
I want to start showing it at zoom level 15.51 as it works normally in maplibre native.

Existing Alternatives or Workarounds

No response

Additional Context

No response

[josxha]

The package uses MapLibre Native. Could you please give more context in how you successfully implemented it in MapLibre Native and why your implementation can't be transfered to this package?

[loaiz1982]

Thanks for following up! I need to clarify - I think I may have misremembered the exact zoom level.

What I observed on maplibre.org:

• My raster.pmtiles has tiles only at zoom level 17
• I set the layer config to minzoom: 16, maxzoom: 18
• When zooming between 16.0-16.99, I could see the z17 tiles displayed (overzoomed/scaled up)
• This worked perfectly in MapLibre JS on the web

The issue in flutter-maplibre:
When I try the same configuration in flutter-maplibre, the tiles don't appear until I reach exactly zoom level 17.0. The overzoom behavior (showing
z17 tiles at z16.x) doesn't work.

Expected behavior:
If a raster layer is configured with minzoom: 16 but only has tiles at z17, it should display those z17 tiles scaled up when viewing at zoom levels
16.0-16.99 (similar to how MapLibre JS handles it).

Is this the standard behavior in MapLibre Native, or is there a specific configuration needed to enable tile overzooming in flutter-maplibre?

[josxha]

I tried to recreate your described behavior in Maputnik that uses MapLibre GL JS. I added a raster pmtiles source. My test pmtiles file had layers from 0 to 21 so I limited the source min and max zoom level to 17.

    "flowers": {
      "type": "raster",
      "url": "pmtiles://https://air.mtn.tw/flowers.pmtiles",
      "minzoom": 17,
      "maxzoom": 17
    }

Then I added a raster layer to the map. The pmtiles content is now visible after passing a zoom level of 16.5 because it rounds to the nearest zoom level. At the beginning in the video I didn't limit the maximum zoom level, that's why we see overzooming. Then, I limit the maximum zoom level to 18 and the the map is now visible between 16.5 and 18.0. Though, there wasn't any underzooming.

underzooming.mp4

Can you provide some reproducable steps for me? Video(s) showing the wanted behavior would help as well.

[loaiz1982]

Thank you for investigating @josxha!

Unfortunately, I can no longer reproduce the original scenario because:

1. The old z17-only raster.pmtiles file is no longer available
2. Current setup: My raster.pmtiles now contains tiles from zoom 13 to 16 (which displays properly)

What I originally thought:
I believed it was possible to display zoom level 17 tiles when viewing at zoom level 15 (underzooming/scaling down the higher resolution tiles). I observed this behavior (or thought I did) on maplibre.org with the z17-only file.

Reality:
After your explanation about rounding to nearest zoom level and my inability to reproduce it now, I realize I may have misunderstood how MapLibre handles tile display at different zoom levels.

Thanks for your time investigating this!