[Talk-in] Understanding "unprojection"

[Aruna S]

Hi everyone!

I am working with the mbtiles-extracts library:
https://github.com/mapbox/mbtiles-extracts. Given an mbtiles file and a
geojson, the library extracts mbtiles cutouts of the polygons in the
geojson.

Except, it does not work for some geojsons.

As documented in https://github.com/mapbox/mbtiles-extracts/issues/10, it
does not work for any polygon present in the following geojson for the
mbtiles listed below:

   - MBTILES: Pretty much every tileset on
   https://osmlab.github.io/osm-qa-tiles/historic.html. Can definitely
   replicate it using for
   https://s3.amazonaws.com/mapbox/osm-qa-tiles/historic/2008-Q1-qa-tiles.mbtiles
   - GEOJSON:
   https://gist.github.com/arunasank/c98ef28abd51b54579c7609f8ebc1de1

When I debug, I see that:
* This function:
https://github.com/mapbox/mbtiles-extracts/blob/master/index.js#L175
returns a falsy value for all the features in the above geojson, resulting
in a falsy value here:
https://github.com/mapbox/mbtiles-extracts/blob/master/index.js#L58-L62

Any help in understanding why these polygons are different from other
polygons, or if there's a pattern I am missing, would be really helpful!

If there are other mailing lists where this could be answered, please point
me to them.

Warmly,
Aruna
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