[Proj] Projection advice

Noel Zinn (cc) ndzinn at comcast.net
Thu Dec 8 13:28:44 EST 2011

GPS, too?  Anyway, I take your response as an affirmative (i.e. scale 
accounted for).  Nevertheless, I'd advise sticking with local (and 
disposable) projections, e.g. an oblique stereographic centered in your 
(small) work area with (probably) a scale of unity at the center.  The 
"best" wide-area projection may not be good enough for some (or many) work 
areas.  -Noel

Noel Zinn, Principal, Hydrometronics LLC
+1-832-539-1472 (office), +1-281-221-0051 (cell)
noel.zinn at hydrometronics.com (email)
http://www.hydrometronics.com (website)

-----Original Message----- 
From: Roger Oberholtzer
Sent: Thursday, December 08, 2011 9:10 AM
To: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] Projection advice

On Thu, 2011-12-08 at 06:41 -0600, Noel Zinn (cc) wrote:
> Roger,
> Presumably you want a conformal projection so that the scale distortion is
> uniform in all directions.


> Does the INS fiddling in Northings/Easting
> account for scale distortion (point scale factor) at all, or does it 
> presume
> there is no scale distortion?  If the latter, then the larger the area 
> your
> generic projection covers, the greater the scale distortion your INS
> fiddling will ignore.  That may not be a good change from your current,
> local-projection procedure.

The INS is comprised of 3D gyroscopes, multi-axis accelerometers, a
wheel pulse transducer, and in some cases inclinometers. From these is
obtained very accurate relative movement information. Drift is minimal
over the distances it is expected to be used. These devices are scaled
and offset against a well-defined surface in the general area (within
the same country...) as they are used. Gravitational and surface curve
effects are minimal over the short distances they are used. At least
that is our working model.

Yours sincerely,

Roger Oberholtzer

OPQ Systems / Ramböll RST

Office: Int +46 10-615 60 20
Mobile: Int +46 70-815 1696
roger.oberholtzer at ramboll.se 

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