Suggestion: `--drop-by-attribute-as-needed=ATTRIB_NAME`
amandasaurus opened this issue · 2 comments
Suggestion: add a new flag to drop objects from a MVT tile (if needed to keep within the tile size), and drop
e.g.: If the tile is too big, “sort” a objects by an attribute, and keep the top N objects which will fit inside this size (and including the N+1 object (when ordered by this attribute) would cause the tile to exceed the limit).
The real world example is that I have millions of little line segements, representing lots of waterways (rivers, streams etc). Each segment has a float for the size of the total river system it's part of. To make MVT pmtiles, I need to drop objects. The logical way is to keep the segments for large river basins.
The code is osm-river-basins on Github, and my tippecanoe command is here in functions.sh. I tried my best, and people are still noticing that it produces gaps in the lines. I believe, a --drop-as-needed-by-attribute=ATTRIB would solve this issue.
Obv. some reverse sorting option would probably be useful for others too.
I would also love to see this, for https://github.com/dabreegster/routing-engines. I've got lines covering every street segment in region to country-sized areas, with a count attribute representing betweenness centrality or some measure of importance. At low zooms with --drop-fraction-as-needed --extend-zooms-if-still-dropping, it looks like this:
I've started experimenting with manually specifying a minimum count for low zooms, like -z13 -j '{"*": [">", "count", 100]}', but I'm not sure yet how to determine good thresholds for a given dataset. Ideally I'd keep as many lines per tile as possible up to the size / feature limits, but if I have to drop something, sort by this count attribute within that tile.
Good idea! I will have to look into adding something like this.