ball tree measurements

--- nearest point lookup test ---
generating 10000 random points...
generating 10000 random checking points...
reference time: 0.94s

::: ball tree :::
{
  generating nodes...   255 nodes generated
  -- nodeval count: 10128
  -- tree dumped to 'dump_balltree.wrl'!
  tree lookup time: 0.449s (47.766%)
  tree validity testing:
  - 0 errors
  - 0 average distance error
  - 0 worst distance error
  tree stats:
  - # node tests: 1294096
  - # node discards: 335895
  - # node accepts: 968201
  - # point tests: 25110971
  - # point accepts: 719394
::: two-level lookup based on ball tree :::
  removing branch nodes...
  - leaf count: 128
  2lev lookup time: 0.42s (44.6809%)
  2lev validity testing:
  - 0 errors
  - 0 average distance error
  - 0 worst distance error
  2lev stats:
  - # node tests: 1280000
  - # node discards: 958847
  - # node accepts: 321153
  - # point tests: 25110971
  - # point accepts: 719394
}