RVI range camera description

From: Curt Lang (Range Vision  Inc.)
To: RP-ML
Date: Thursday, June 23, 1994
Subject: RVI range camera description
     This is to continue my introduction to the rp list:
     A range camera combines a computer, a CCD video camera, an image capture board and a beam projector.  It is used to scan objects placed in front of it and automatically produces dense mats of xyz surface coordinates.  The sets of coordinates can be exported to CAD and graphics software.
     The projector shines a very thin, very flat plane of light onto the object and the camera observes the stripe of light falling on the object's surface.  Because the camera and the projector are some horizontal distance apart, the light stripe (from the camera's viewpoint) appears to follow the curvature of the object's surface.  Imagine that the camera and the projector are sitting on either end of the base of a triangle, and an illuminated point on the object surface (contacted by the plane of light) is at the apex of the triangle.  The distance between the focal node of the camera and a point in the projector is known, so the xyz locations of points along the illuminated stripe on the object's surface can be calculated by triangulation.
     The beam projector scans the stripe across the object surface, so you can repeat the process many times across small intervals, and for every stripe position you can measure one coordinate for every horizontal row in the CCD image plane (about 484 in our favourite camera.)  The result is a file containing a dense mat of ordered xyz coordinates.
     The RVI range camera differs from others in that it is very precise and accurate.  The following table gives examples of the precision achievable with a particular range camera for different standoffs and object plane extents:
     (Assumptions: angular field of view (horizontal) 19.96 degrees; angular field of view (vertical) 15.04 
degrees)

         horiz.   vert.
  Stand  object   object
    off  extent   extent    res. X    res. Y   res. Z
 meters  meters   meters      mm        mm       mm
------------------------------------------------------
   1.00    0.35     0.26    0.0458    0.5355   0.0917
   0.50    0.18     0.13    0.0229    0.2677   0.0458
   0.25    0.09     0.07    0.0115    0.1339   0.0229
   0.15    0.05     0.04    0.0069    0.0803   0.0138

     The best accuracy is about plus/minus 1 unit of z resolution in a central region of the scanning volume, 
decreasing somewhat in the outer portions of the scanning volume.
     RVI builds these range cameras to order and one of the type described would cost about $140,000 (US).  They are now used by engineers to inspect machine parts.  RVI has also built larger scale range cameras that work at a standoff of about 6 meters and will sweep a volume of about 2x2x2 meters.
Regards,
=== Curt Lang, Eos Systems Inc.