[Proj] ITRF to GDA94 transformation problems - bug in 7 parameters?

[Mikhail Tchernychev]

  Hello Mikael,

Thank you very much for your explanation!  I was puzzled with this 
problem for almost a year,
and I did try changing rotation signs, but I did not know that all signs 
needs to be reversed.
Now everything makes sense.

BTW, there is also ugly bug in my shell script (+towgs84 not properly 
defined)

Thanks again for providing this great answer to the list,

Best Regards
Mikhail

On 8/26/2011 12:45 AM, Mikael Rittri wrote:
> Hello Mikhail,
> you wrote
>
>> I am trying to re-produce transformation described in this document:
>>
>> http://www.ga.gov.au/image_cache/GA3795.pdf
>>
>> appendix B, and I am getting errors about 0.11 m
>> My
>> +towgs84=-0.054100,-0.019100,0.009600,0.010833,0.010703,0.011403,0.006859,
>> the same numbers as in the article.
> You have made two subtle errors that nearly cancel each other, but not quite.
>
> A) There are two sign conventions for the three rotations. The document
> uses Coordinate Frame Rotation (according to sections 2 and 3), but cs2cs
> uses the opposite Position Vector Transformation.  So with cs2cs you should
> negate the rotations, and use
>
> +towgs84=-0.054100,-0.019100,0.009600,-0.010833,-0.010703,-0.011403,0.006859
>
> instead. (But wait, I am not done yet!)
>
> B) In the document, transformation goes in the direction
> from ITRF2000 to GDA94. With cs2cs, if you want to regard
> ITRF2000 as equivalent to +datum=WGS84, then to model GDA94,
> you need +towgs84 parameters that implement the opposite
> direction: from GDA94 to ITRF2000. To do this, you negate
> all parameters from A), and get
>
> +towgs84=0.054100,0.019100,-0.009600,0.010833,0.010703,0.011403,-0.006859
>
> instead. (Now I am done.)
>
> With the parameters from B), I can reproduce the results of the document by doing
>
> cs2cs +from -w4 +proj=latlong +datum=WGS84 +to +towgs84=0.054100,0.019100,-0.009600,0.010833,0.010703,0.011403,-0.006859 +proj=latlong
>
> input:
>
> 133d53'7.8574"E  23d40'12.4314"S 603.287
>
> output:
>
> 133d53'7.8478"E 23d40'12.4461"S 603.350
>
> Best regards,
>
> Mikael Rittri
> Carmenta
> Sweden
> http://www.carmenta.com
>
> -----Original Message-----
> From: proj-bounces at lists.maptools.org [mailto:proj-bounces at lists.maptools.org] On Behalf Of Mikhail Tchernychev
> Sent: den 25 augusti 2011 23:02
> To: PROJ.4 and general Projections Discussions
> Subject: [Proj] ITRF to GDA94 transformation problems - bug in 7 parameters?
>
>     Hello everyone,
>
> I am trying to re-produce transformation described in this document:
>
> http://www.ga.gov.au/image_cache/GA3795.pdf
>
> appendix B, and I am getting errors about 0.11 m
>
> My
> +towgs84=-0.054100,-0.019100,0.009600,0.010833,0.010703,0.011403,0.00685
> +9,
>    the same
> numbers as in the article.
>
> This is what I get if I use lat / lon ->  lat/lon
>
> cs2cs +from -w4  +proj=latlong +datum=WGS84 +to
> +towgs84=-0.054100,-0.019100,0.009600,0.010833,0.010703,0.011403,0.00685
> +9 +proj=latlong
> <<EOF
> 133d53'7.8574"E  23d40'12.4314"S 603.287 EOF
>
>
> Computed and Correct results:
> 133d53'7.8454"E    23d40'12.4468"S   603.261
> 133d53'7.8478"E    23d40'12.4461"S   603.350
>
> I also tried to convert directly geocentric coordinates listed in the article. This is what I got:
>
> cs2cs -f "%.3lf" +from  -w4 +proj=geocent +datum=WGS84 +to
> +towgs84=-0.054100,-0.019100,0.009600,0.010833,0.010703,0.011403,0.00685
> +9
> +proj=geocent<<EOF
> -4052052.048 4212836.105 -2545105.587
> EOF
>
> computed and correct result
> -4052051.655    4212836.186   -2545106.011
> -4052051.765    4212836.205   -2545106.027
>
> I attached script with cs2cs calls, which exhibits the problem.
>
>
> Help is greatly appreciated,
>
> Thank you
> Mikhail
>
>