Re: Total Station or 3D Laser Scanning?

"William R. Cowan" <[EMAIL PROTECTED]> wrote in message news:<[EMAIL PROTECTED]>...
> S. R. Sheffield wrote:
> 
> > On 28 Oct 2003 04:03:54 -0800, [EMAIL PROTECTED] (Stu) wrote:
> > 
> > 
> >>Hi,
> >>
> >>My company has recently won a contract to survey as-built positions
> >>and levels of granite slabs and cobbles in a 60m x 40m indoor area. We
> >>are required to survey all slab corners and individual cobbles ( a
> >>total of 28,000 points) to an accuracy of +/- 3mm. The client is
> >>hoping to make a claim against the flooring contractor for being out
> >>of spec, trip hazards etc.
> >>I was originally going to survey it conventionally with total station
> >>and prism, but I have been thinking about other solutions. Would laser
> >>scanning be a viable alternative? Would laser scanning give the
> >>required accuracy? The survey was priced for about 3 weeks field time
> >>and 1 week office.
> >>
> >>Any advice gratefully received.
> >>
> >>S. Thomas
> >>Geomatics Manager
> > 
> > Get your money up front on court case surveys concerning bodily
> > injuries.  It's always hard to collect from a lawyer who doesn't want
> > to pay after judgements are rendered against his client.  At least
> > that been my sad experience.
> > 
> > 
> > srs
> 
> Your observations are excellent.  I will have to remember that.  I have 
> some friends who do court work.  I will pass this gem on.
> 

A LIDAR laser scanner will yield 6 mm accuracy.  Who came up with the
3 mm specification?  Probably some layperson (ATTORNEY) that has no
concept of what precision measurement costs.  I recommend going back
and getting a mathematical proof and justification for the stated
accuracy criterion - (fat chance!).  A rental quotation from Leica for
a Cyrax scanner (and software) for two days including shipping should
give your client a reality check concerning what delivering 6 mm
accuracy will cost.

A signed contract from the attorney (with witnesses) will solve any
potential billing problems.  Be sure to get the case citation so that
if anything goes wrong you can file a Mechanic's Lien on any judgement
or out of Court settlement.

Cliff Mugnier
LOUISIANA STATE UNIVERSITY