3d polygons wobbly in 'globe' projection (maplibre)

[mtennekes]

See https://r-tmap.github.io/tmap.mapgl/articles/polygons3d bottom

If you zoom and then pan around, there are strange artefact, as if the borders became wobbly. The problem doesn't occur when set to crs 3857:

tm_shape(NLD_dist) +
	tm_polygons_3d(height = "pop_dens",
				   fill = "edu_appl_sci",
				   fill.scale = tm_scale_intervals(style = "kmeans", values = "-pu_gn"),
				   fill.legend = tm_legend("University degree")) +
	tm_maplibre(pitch = 45) +
	tm_crs(3857)

I guess it has something to do with transformation between crs's.

Do you know what could be going on @walkerke @tim-salabim ? If needed I can make a reproducible mapgl example.

Earlier there was a similar issue when polygons were drawn at height 0:

tm_shape(World) + 
  tm_polygons_3d(
    height = "pop_est_dens", 
    fill = "continent", 
    options = opt_tm_polygons_3d(height.min = 0))

Greenland has a population density (pop_est_dens) of almost 0. As a workaround, I've set the default of the minimum polygon height to some value (to be precise 0.1% of the sort of the bounding box). I don't have this issue with mapbox.

[walkerke]

I'm having the same problem - I think this is a MapLibre issue that goes deeper than our implementation.

[tim-salabim]

It would help to have a reproducible mapgl example...
I have seen this before, but only with deckgl overlays so far, not native maplibre. See developmentseed/lonboard#1037 (comment) and the linked video there. I have also found a work around for this (2 comments down). But as I said, that is adjusting things in the deckgl overlay.

[walkerke]

Try this:

Setup:

library(tigris)
library(mapgl)

wy_tracts <- tracts("WY", cb = TRUE)

wy_tracts$height <- sample(
  c(0, 0, 0, 0, 0, 5000, 10000, 50000),
  nrow(wy_tracts),
  replace = TRUE
)

Globe projection (looks bad):

maplibre(bounds = wy_tracts) |>
  add_fill_extrusion_layer(
    id = "wyoming",
    source = wy_tracts,
    fill_extrusion_opacity = 0.5,
    fill_extrusion_height = get_column("height")
  )

Mercator projection (looks normal):

maplibre(bounds = wy_tracts, projection = "mercator") |>
  add_fill_extrusion_layer(
    id = "wyoming",
    source = wy_tracts,
    fill_extrusion_opacity = 0.5,
    fill_extrusion_height = get_column("height")
  )