Image on a map: NaN width/height

[pixelspark]

When creating a map using Vega-Lite and circle markers, all is well (very pretty!). After changing the marker type to "image", adding "width" and "height" values, as well as adding a "url" encoding, it appears the images that are put on the map do not receive proper width/height.

The same usage of images appears to work fine on regular (non-geo) charts. To reproduce, paste in the online editor:

{
  "$schema": "https://vega.github.io/schema/vega-lite/v4.json",
  "layer": [
    {
      "mark": {
        "type": "geoshape",
        "fill": "#ddd",
        "stroke": "#fff",
        "strokeWidth": 1
      },
      "data": {
        "url": "data/us-10m.json",
        "format": {"type": "topojson", "feature": "states"}
      }
    },
   
    {
      "mark": {"type": "image", "width":10, "height":10},
      "data": {"url": "data/airports.csv"},
      "encoding": {
        "latitude": {"field": "latitude", "type": "quantitative"},
        "longitude": {"field": "longitude", "type": "quantitative"},
        "url": {"datum": "data/ffox.png", "type": "nominal"}
      }
    }
  ],
  "projection": {"type": "albersUsa"},
  "width": 900,
  "height": 500,
  "config": {"view": {"stroke": null}}
}

Result in (most recent) Chrome:

[domoritz]

It looks like we don't support datum in latitude/longitude yet.

However, even if I modify the Vega spec manually (Open the Chart in the Vega Editor), I see NaN for width and height. This needs some more investigation.

[pixelspark]

Hm, I believe the same problem still occurs when using field (this was my original use case but I had some other issues at the same time, so I am not totally sure).

Might it be that width/height are simply not converted the right way when a geographical projection is in place? Both should correspond to screen pixels, not degrees (at least that is how it works when used in non-geo markers)..

[domoritz]

Yeah, something is going wrong here.

[domoritz]

Maybe we introduced an issue in #5668.

[domoritz]

[pixelspark]

Awesome! 👍

Out of curiosity, now that this works: what extra changes would be needed to be able to plot tiles on the map? I assume width and height are now pixel-sized - or is it also possible to express these as (lon, lat) delta? Might as well add that if it is easy, as it would enable using e.g. OSM tiles.

[domoritz]

I think you could do it (someone has done it for Vega already) but the performance isn't great for interactions. You can try it when we make a release.