Feature: Within Expression for Polygon & Polygon Centroid

[strech345]

Motivation

Would be nice to style or filter all polygons which are inside a specific polygon.
Within means the polygon is full inside of the other. But for a polygon selection it looks like more correct when only the centroid of the polygon is within the other.

So it would be nice not only to use within with a polygon but also with it centroid.

Otherwise if the calculation of centroid is to heavy, it would be nice to precalculate the centroid, load it into the mbtile as property and then use it for the within. This means using the within with properties.

[ryanhamley]

This is a request to extend #9352 to work with polygons within polygons in addition to points and lines within polygons. cc @zmiao

[markusand]

Sorry I opened a similar request in #10479. I reference it here to track them together.

This feature is very useful, and I'm curious why Polygon check was left out. It should not be too hard to implement as long as Polygon perimeter can be considered a LineString.

I'm also wondering if a less strict interpretation of what within means (I'm thinking in partially contained) would open more use cases.

[zmiao]

I am now looking into this issue. I will update once I have a solution for it.

[markusand]

'distance' expression in this pull request

#10616

would be a solution to this issue. It's not a strict 'within' expression, but distance is 0 if two polygons intersect or one is within another.

[enersis-pst]

@zmiao
Thanks for that work.
Will it also work with Holes in Polygons?

{
  "type": "MultiPolygon",
  "coordinates": [
    [
      [
        [
          -47.900390625,
          -14.944784875088372
        ],
        [
          -51.591796875,
          -19.91138351415555
        ],
        [
          -41.11083984375,
          -21.309846141087192
        ],
        [
          -43.39599609375,
          -15.390135715305204
        ],
        [
          -47.900390625,
          -14.944784875088372
        ]
      ],
      [
        [
          -46.6259765625,
          -17.14079039331664
        ],
        [
          -47.548828125,
          -16.804541076383455
        ],
        [
          -46.23046874999999,
          -16.699340234594537
        ],
        [
          -45.3515625,
          -19.31114335506464
        ],
        [
          -46.6259765625,
          -17.14079039331664
        ]
      ],
      [
        [
          -44.40673828125,
          -18.375379094031825
        ],
        [
          -44.4287109375,
          -20.097206227083888
        ],
        [
          -42.9345703125,
          -18.979025953255267
        ],
        [
          -43.52783203125,
          -17.602139123350838
        ],
        [
          -44.40673828125,
          -18.375379094031825
        ]
      ]
    ]
  ]
}

[zmiao]

@enersis-pst are you referring to the distance expression? If so, in principle it would work as @markusand mentioned above. I just tried a very simple test case with the polygon you provided:

                    {
                        id: "polygons",
                        type: "fill",
                        source: "rectangles",
                        paint: {
                            "fill-color": [
                                "case",
                                [">", ["distance", polygonWithHole], 0],
                                "red",
                                "blue",
                            ],
                            "fill-opacity": 0.2,
                        },
                    },

and it looks like:

[enersis-pst]

@zmiao yes. looks good. Thanks for that example. Nice and very flexible feature. Hope it will be merged soon.

[mkandarEsource]

Is there any status update on this feature. Just ran into a need for it today.

[zmiao]

@mkandarEsource we've introduced the distance expression: https://docs.mapbox.com/style-spec/reference/expressions/#distance, would this fit for your need as a workaround?

[mkandarEsource]

@zmiao Possibly, let me explain the use case. We have a snipping tool on the map we're building. The user draws a polygon and then the features within that polygon are filtered in. Issues we've run into so far:

1. Within expression cannot seemingly be combined with other filters in an 'any' or 'all'. We receive an error that it is not one of the valid logical expressions.
2. Within doesn't work with polygon features

If a distance of 0 entails that the feature is within (or likely intersected by) the polygon drawn by our snipping tool, we can work with that. There isn't a hard requirement to do "within" so an "intersects" would work. I'll test it out and let you know.

[mkandarEsource]

@zmiao That does work as a geo intersects, which is sufficient