datetime as default aesthetic

[mdsumner]

there's an error from leaflet when datetime is the default column available - should this go to leaflet rather than here?

this had us going for a while, because we're dealing with pure long,lat,time data and datetime is not handled:

v <- sf::st_as_sf(data.frame(x = 0:10, y = seq(0, 20, length.out = 11), t = Sys.time() + 0:10), coords = c("x", "y"), crs = "OGC:CRS84")
mapview(v)     

Error in dispatch(map, "fitBounds", leaflet = { : Invalid map parameter

It's simple enough to as.integer that and get something useful (albeit not especially meaningful)

v$t <- as.integer(v$t)
mapview(v)     

I know that formatting this stuff would be a can of worms, but I think that's a better result than the weird error. We just wanted to see the points and how they change in time from some real tracking data.