featuresAt returns bucketType as designated in stylesheet, refs #876

[lbud]

Per #876, this adds a _bucketType property to features returned in map.featuresAt that indicates the layer type specified in the stylesheet, so it would return something like

{
    "_bucket" : "landcover_copy",
    "_bucketType" : "line",
    "_type" : "Polygon",
    "properties" : {
        "class" : "scrub"
    },
    "extent" : 4096,
    "type" : 3
}

This is a really simple fix for the specific problem I'm having in a project, but I think requires further discussion on the actual intent/use for featuresAt — is this 👍 or should it return more info? (Also, if this is sufficient, we should probably rename the returned _type property — _geometryType?)

cc @jfirebaugh @ansis @kkaefer @edenh @mourner @tmcw

[lbud]

hm hold on, something's broken was #880

[jfirebaugh]

The results should use terms that are consistent with the rest of the API and style-spec. So, "layer", "source", "layout", "paint", "$type".

How about:

{
  "$type": "Polygon",
  "properties": {
    ...
  },
  "layer": {
    "id": "landcover_copy",
    "type": "line",
    "layout": {
      ... calculated layout properties ...
    },
    "paint": {
      ... calculated paint properties ...
    }
  },
  "source": {
    "id": "mapbox",
    "url": "mapbox://mapbox.mapbox-streets-v6-dev"
  }
}

[lbud]

Now returning

{
  "$type": "line",
  "layer": {
    "id": "waterway",
    "type": "line",
    "layout": {
      "line-cap": "round",
      "line-join": "round",
      "line-miter-limit": 2,
      "line-round-limit": 1
    },
    "source": {
      "id": "mapbox.mapbox-streets-v6-dev",
      "source-layer": "waterway"
    },
    "paint": {
      "line-opacity": 0.9,
      "line-color": [0, 0.48, 0.78, 0.9],
      "line-width": 1.25
    }
  },
  "properties": {
    "class": "river",
    "osm_id": 93380892,
    "type": "river"
  },
  "extent": 4096,
  "type": 2
}

Some questions:

• Calculated paint props return premultiplied alpha values. Should this remain true for featuresAt or since it's more of an externally facing API should we convert to normal RGBA decimal?
• The original intent of this API was for source inspection/tile statistics I think which is why it had things like extent and type (I can only assume this is geometry type…??) — should these be removed or are they still useful for something?

[jfirebaugh]

Nice. $type values should be Point, LineString or Polygon (like in filters). It's kind of odd to return premultiplied values but probably fine for now. Let's remove extent and type. What does it look like with {geometry: true} option? Maybe this should be a GeoJSON object.

[lbud]

Ah good catch, grabbed the wrong type — thanks!

With {geometry: true}: this is a bit hard to make sense of. I'm not sure what the use case for this format is…?

{
  "$type": "LineString",
  "layer": {
    "id": "road",
    "type": "line",
    "layout": {
      "line-cap": "butt",
      "line-join": "miter",
      "line-miter-limit": 2,
      "line-round-limit": 1
    },
    "source": {
      "id": "mapbox.mapbox-streets-v6-dev",
      "source-layer": "road"
    },
    "paint": {
      "line-color": [
        0.78,
        0,
        0,
        0.78
      ],
      "line-dasharray": [
        3.5,
        2
      ],
      "line-translate": [
        1.75,
        -2.25
      ],
      "line-opacity": 0.78,
      "line-width": 2.5,
      "line-gap-width": 0.25
    }
  },
  "_geometry": [
    [
      {
        "x": 1036,
        "y": 2998
      },
      {
        "x": 1102,
        "y": 3006
      },
      {
        "x": 1145,
        "y": 3002
      },
      {
        "x": 1188,
        "y": 2987
      },
      {
        "x": 1253,
        "y": 2957
      },
      {
        "x": 1301,
        "y": 2924
      },
      {
        "x": 1345,
        "y": 2880
      },
      {
        "x": 1381,
        "y": 2829
      },
      {
        "x": 1411,
        "y": 2769
      },
      {
        "x": 1424,
        "y": 2712
      },
      {
        "x": 1428,
        "y": 2654
      },
      {
        "x": 1423,
        "y": 2583
      },
      {
        "x": 1335,
        "y": 2199
      },
      {
        "x": 1322,
        "y": 2135
      },
      {
        "x": 1320,
        "y": 2086
      },
      {
        "x": 1320,
        "y": 2044
      },
      {
        "x": 1329,
        "y": 1999
      },
      {
        "x": 1336,
        "y": 1979
      },
      {
        "x": 1343,
        "y": 1958
      },
      {
        "x": 1385,
        "y": 1875
      },
      {
        "x": 1400,
        "y": 1854
      },
      {
        "x": 1453,
        "y": 1814
      },
      {
        "x": 1545,
        "y": 1753
      },
      {
        "x": 1649,
        "y": 1723
      },
      {
        "x": 1739,
        "y": 1711
      },
      {
        "x": 1869,
        "y": 1715
      },
      {
        "x": 1915,
        "y": 1717
      },
      {
        "x": 2135,
        "y": 1741
      },
      {
        "x": 2309,
        "y": 1783
      },
      {
        "x": 2499,
        "y": 1841
      },
      {
        "x": 2657,
        "y": 1901
      },
      {
        "x": 2827,
        "y": 1993
      },
      {
        "x": 3117,
        "y": 2173
      },
      {
        "x": 3234,
        "y": 2243
      }
    ]
  ]
}