[Proj] Geotrans, PCTrans and cs2cs - different angle signs?

[Mikhail Tchernychev]

Thank you all for clarification on this issue. I did not know about it
and I learn it hard way - I had to transform data and cs2cs worked, but 
geotrans
no... My original idea was to use geotrans but I used cs2cs, which as I 
see now
is way better from other perspectives as well.  Apparently geotrans 
assumes American
convention, because it is DoD program.

Thanks again,

Cheers

Mikhail

On 01/18/2011 01:44 AM, Mikael Rittri wrote:
> Jan wrote:
>> Yes, the angles can be given either in "right-hand" (American)
>> or "left-hand" (European) convention.
> The two rotation sign conventions have formal names, which are
> useful to know since they are used by EPSG.
>
> * The "American" sign convention is formally known as
>    "Coordinate Frame Rotation", and it is actually used
>    by many European countries too (although a minority).
>
> * The "European" sign convention is formally known as
>    "Position Vector Transformation", and it is the convention
>    used by cs2cs.  It is also the NATO standard, and (I think)
>    the Eurogeographics standard.
>
> EPSG hasn't standardized on one sign convention. For each 7-parameter
> datum shift, they use the sign convention of the original information
> source, and then they document which one it was. When you look up a
> 7-parameter datum shift at www.epsg-registry.org, you must remember
> to scroll down, since the sign convention is given below the parameters.
>
> Jan also wrote:
>> Mind that angles can be given either in (micro)degrees (PROJ) or radians (EPSG).
> Not quite. In cs2cs (PROJ), the rotation angles must be given in
> arc seconds (1 arc second = 1/3600 degree.)
>
> As for EPSG, it is true that the formulas in Guidance Note 7.2 assumes
> that the rotation angles are in radians. However, for a 7-parameter
> datum shift published in the EPSG database, the angle unit isn't
> standardized.  Instead, it is the angle unit used by the information
> source.
>     This means that the rotation angles in EPSG are usually in arc seconds,
> but there are some datum shifts for the Netherlands and for Jan Mayen
> where they are in microradians, and a datum shift for Canada where they
> are in radians.
>
> Regards,
>
> Mikael Rittri
> Carmenta
> Sweden
> http://www.carmenta.com
>
> ________________________________
>
> From: proj-bounces at lists.maptools.org [mailto:proj-bounces at lists.maptools.org] On Behalf Of Jan Hartmann
> Sent: Tuesday, January 18, 2011 9:00 AM
> To: misha at mail.geometrics.com; PROJ.4 and general Projections Discussions
> Cc: Mikhail Tchernychev
> Subject: Re: [Proj] Geotrans, PCTrans and cs2cs - different angle signs?
>
>
> Yes, the angles can be given either in "right-hand" (American) or "left-hand" (European) convention. See the thread on:
>
> http://lists.maptools.org/pipermail/proj/2010-April/005198.html
>
> Mind that angles can be given either in (micro)degrees (PROJ) or radians (EPSG). You can find a discussion about the conversion from EPSG numbers to PROJ, with both sign and radians conversion in:
>
> http://trac.osgeo.org/geotiff/ticket/22
>
> with an attached spreadsheet to perform the computation for the Dutch coordinate system (EPSG:28992)
>
> Jan
>
> On 01/18/11 06:24, Mikhail Tchernychev wrote:
>
> 	Hello List,
> 	
> 	It came to my attention that 7-parameters values should be different for
> 	cs2cs and
> 	programs like Geotrans  and PCTrans. It seems all 3 angles should have
> 	different
> 	sign to match cs2cs results. Shifts stay the same, as well as scaling
> 	(well, for
> 	geotrans it is not in ppm).  I wonder if it is something well known or
> 	am I missing
> 	something?
> 	
> 	Thank you,
> 	
> 	Mikhail
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