[Proj] PROJ4 7 parameter datum shift Beijing 1954

[Geoff Shipton]

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:

 

TX:          170.076

TY:          154.924

TZ:          97.308

RX:         1.666408

RY:          0.872624

RZ:          -8.648183

K:            0.00000186

 

The Ellipsoid is Krassovsky 1940

 

The local coordinate system parameters are TM:

 

CM: 121.46716061

Scale: 1.0

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.

WGS84 coordinate

31° 17' 27.50965" N          121° 35' 54.41138" E        13.7729

Should give Shanghai Local coordinate

12501.0727E       6164.1228N

 

However the position from PROJ4 is:

12953.30E            6042.97N

 

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.

 

Geoff Shipton,
Triton Imaging Inc.
Customer Support.
Capitola CA.
geoff at tritonimaginginc.com

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