[Proj] PROJ4 7 parameter datum shift Beijing 1954
Noel Zinn (cc)
ndzinn at comcast.net
Mon Mar 28 14:11:00 EST 2011
First thing to try is to reverse the signs of the three rotations. I believe that proj.4 uses a “position vector” rotation sense. This may be a “coordinate frame” transformation. Judging from the RZ value and the differences in Eastings, this might work (but I haven’t run the numbers). -Noel
Noel Zinn, Principal, Hydrometronics LLC
+1-832-539-1472 (office), +1-281-221-0051 (cell)
noel.zinn at hydrometronics.com (email)
From: Geoff Shipton
Sent: Monday, March 28, 2011 1:44 PM
To: proj at lists.maptools.org
Subject: [Proj] PROJ4 7 parameter datum shift Beijing 1954
Greetings to all,
I am looking for some assistance with a problem we have using the PROJ4 libraries, I am not a programmer neither am I geodesist – however I know enough to be dangerous! Please bear with me…
We have a customer in Shanghai China that is uses something he refers to as the Shanghai Local projection.
It is built on Beijing 1954 and uses that datum, the 7 parameter shift he gives are as follows:
The Ellipsoid is Krassovsky 1940
The local coordinate system parameters are TM:
False Eastings: 0
False Northings: -34587140.589
I constructed the following PROJ4 string:
+proj=tmerc +lat_0=0 +lon_0=121.46716061 +k=1 +x_0=0 +y_0=-3457140.589 +ellps=krass +towgs84=170.0760,154.9240,97.3080,1.6664,0.8726,-8.6482,0.00000186 +units=m +no_defs
However I am not getting the correct results, for example.
31° 17' 27.50965" N 121° 35' 54.41138" E 13.7729
Should give Shanghai Local coordinate
However the position from PROJ4 is:
We very rarely need to invoke this type of transformation so it’s quite possible something is awry with our code, but I sure would appreciate any thoughts on the problem.
Triton Imaging Inc.
geoff at tritonimaginginc.com
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