Add FlatGeobuf element

[spwoodcock]

Issue

• Currently there is no way to load FlatGeobuf data in this library.
• It's pretty easy to load a FlatGeobuf using the official lib, deserialize to GeoJSON, then pass through to our GeoJSON component.

Solution

• Made a FlatGeobuf component that essentially wraps GeoJSON.
• It has a bit of additional logic there for:
  • Taking a bounding box array and only fetching the data within the BBOX (using RANGE requests). extent={bbox}
  • If a polygon GeoJSON is passed instead, then the BBOX is calculated for fetching data, and the final dataset is trimmed to the extent of the polygon. extent={polygonGeojson}
    • Of course, having a dynamic bbox is possible, via events such as clicking on bounding map geometries. I have tested this and it works nicely.
  • A extractGeomCols prop, when set to true will extract the first geometry from within a GeometryCollection. This is a bit of a hack required so that properties can be extracted alongside the geometry when working with PostGIS.
  • Accepts a function for prop metadataFunc={funcHere} to handle flatgeobuf metadata on fetch.
• Child components can be passed through via a slot, to allow for styling in the same way as the GeoJSON component.
• Also takes a few additional props used by the GeoJSON component that are passed directly through.

Note

This component uses Svelte 5 syntax, with the PR anticipating the merge of #197

I had some issues with the rendering orders that are hopefully fixed by the functions I used from context and source logic.
Please let me know if I should change anything here!

Screenshot

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Latest commit: bb6226d

The changes in this PR will be included in the next version bump.

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Name	Type
svelte-maplibre	Minor

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[dimfeld]

Thanks for this. Just FYI since this requires runes it's going to be a bit before this merges though.

The existing PR that you referenced only updates the docs site to use Svelte 5. I'm going to do a release at some point that is a breaking change to make this package only work with Svelte 5, but that's going to require an effort to at least update the slots/snippets and events handling to work with Svelte 5

I don't have a lot of time to work on that right now, but hope to create a next branch later this month to start the work, and I can merge this one into that branch when I do.

[dimfeld]

remove this one

[dimfeld]

The next branch now exists, so if you want to rebase this on to that branch I'm happy to merge it in there.

[spwoodcock]

Nice! Happy to keep contributing to this lib 😄

Svelte 5 is fully backward compatible with Svelte 4 syntax, so the upgrade could still be done without migrating all the syntax. Of course this would be a breaking major version increment.

The upgrade should be done over time, but it could be gradual and community supported if time is limited 👍

I currently use this lib in a Svelte 5 project without issues

[spwoodcock]

Finally rebased this & updated the syntax to match latest library changed 👍

One small issue on the example page:

Error: Source "entities" cannot be removed while layer "fill-1760181839982" is using it.
    removeSource style.ts:1009
    removeSource map.ts:2194
    addSource source.ts:27
    addSourceToMap FlatGeobuf.svelte:105
    updateGeoJSONData FlatGeobuf.svelte:88
    FlatGeobuf FlatGeobuf.svelte:92

Sorry, I didn't have time to dig into why this is happening, but it doesn't affect the rendering and seems like a cleanup operation that probably isn't essential to functionality.

All set I think @dimfeld!