non-numeric vertices

[mdsumner]

Probably should disallow these earlier

nz <- spData::nz
cl <- raster::rasterToContour(raster::crop(quadmesh::etopo, 
                  sf::st_transform(nz, 4326)))

copy_down(SC0(cl), "level")
# class       : SC
# type        : Primitive
# vertices    : 1054 (3-space)
# primitives  : 527 (1-space)
# crs         : +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs +towgs84=0,0,0
# Warning message:
#   In find_z(x, z) : z is not numeric

plot3d(copy_down(SC0(cl), "level"))
# Warning message:
#   In find_z(x, z) : z is not numeric