[Proj] Projection advice

Noel Zinn (cc) ndzinn at comcast.net
Thu Dec 8 07:41:23 EST 2011


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.


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 5:37 AM
To: proj at lists.maptools.org
Subject: [Proj] Projection advice

I have a system that starts with WGS84 lat/long, projects them so as to
obtain northings/eastings, does some fiddling with the locations, and
then converts them back in to WGS84 lat/long. The conversion from/to
lat/long is done by proj. The fiddling with the northings/eastings is
done based on some INS that provides relative movement information in
meters. Only the WGS84 lat/longs are kept.

Currently, I use a projection for the local region. The thought was that
this would best 'match' the INS movements, which are of course always
local. I would like to generalize this solution by perhaps not using a
local projection. Instead use a generic projection everywhere. It seems
reasonable to do this as (1) the projection will not be kept, and (2)
the movements applied to the projections are relative.

My question is; is there a 'best' projection to use for such a

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

Ramböll Sverige AB
Krukmakargatan 21
P.O. Box 17009
SE-104 62 Stockholm, Sweden

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