geodataframe_to_cells issue about h3ronpy

[diehl]

Hi @nmandery - let me work on getting you a specific example. Just wanted to check in first to see if you found this similarly perplexing given the intent of the code.

[nmandery]

Thank you. I just converted this geometry to H3 using only h3o using

use geo_types::GeometryCollection;
use geojson::{quick_collection, GeoJson};
use h3o::geom::{ContainmentMode, PolyfillConfig, ToCells};
use h3o::Resolution;

fn main() {
    let gj = include_str!("../example_df.geojson");

    let geojson: GeoJson = gj.parse::<GeoJson>().unwrap();
    let collection: GeometryCollection<f64> = quick_collection(&geojson).unwrap();
    let h3o_geom = h3o::geom::Geometry::from_degrees(collection.0[0].clone()).unwrap();

    for res in Resolution::range(Resolution::Four, Resolution::Twelve) {
        let cells: Vec<_> = h3o_geom
            .to_cells(
                PolyfillConfig::new(res).containment_mode(ContainmentMode::IntersectsBoundary),
            )
            .collect();

        println!("r={}  ->  num cells={}", res, cells.len());
    }
}

This resulted in

r=4  ->  num cells=0
r=5  ->  num cells=0
r=6  ->  num cells=0
r=7  ->  num cells=0
r=8  ->  num cells=2
r=9  ->  num cells=3
r=10  ->  num cells=4
r=11  ->  num cells=13
r=12  ->  num cells=54

So this is the same behavior as h3ronpy.

Without inspecting the geometries, I suppose the variant that the geometry is completely within the cell is not covered by IntersectsBoundary. Now that I look at this again, this is also how I read the modes description at https://docs.rs/h3o/latest/h3o/geom/enum.ContainmentMode.html .

Seems I need to bring back some parts of nmandery/h3arrow@f5c46c0 as some kind of fourth polyfill mode.

[nmandery]

Just to keep this issue updated: I am currently really low on spare time to further look into this, I will try to come back to this as soon as possible.

[nmandery]

Hi. That sounds suspicious - there should indeed be always at least one cell.

What would be this threshold? It is reproducible with a single geometry, or only with large dataframes?

[diehl]

@nmandery Here's an example dataframe I'm having an issue with, represented in geojson.

When I execute

geodataframe_to_cells(df, 4, containment_mode=ContainmentMode.IntersectsBoundary)

I'm getting back an empty dataframe. When I increase the resolution from 4 to 11, I see results.

[diehl]

@nmandery Strange. Glad we caught this. Since h3-py does not offer the capability to compute a complete H3 cover, getting this right will be a significant contribution.

[diehl]

No worries @nmandery - I'm investigating other options in the meantime.