#### 7.2.99 pick

`(pick COORDSYS GEOMID G V E F P VI EI FI)`
  The pick command is executed internally in response to pick events (right mouse double click).
  COORDSYS
    = coordinate system in which coordinates of the following arguments are specified. This can be:
    `world`
      world coord sys
    `self`
      coord sys of the picked geom (GEOMID)
    `primitive`
      coord sys of the actual primitive within the picked geom where the pick occurred.
  GEOMID
    = id of picked geom
  G
    = picked point (actual intersection of pick ray with object)
  V
    = picked vertex, if any
  E
    = picked edge, if any
  F
    = picked face
  P
    = path to picked primitive [0 or more]
  VI
    = index of picked vertex in primitive
  EI
    = list of indices of endpoints of picked edge, if any
  FI
    = index of picked face

  External modules can find out about pick events by registering interest in calls to `pick` via the `interest` command.

  In the ND-viewing context the co-ordinates are actually ND-points. They correspond to the 3D points of the pick relative to the sub-space defined by the viewport of the camera where the pick occurred. The co-ordinates are then padded with zeroes and transformed back to the co-ordinate system defined by COORDSYS.