[Proj] Understanding 2D Helmert

[Andre Joost]

Am 26.10.18 um 20:11 schrieb Even Rouault:
> On vendredi 26 octobre 2018 19:54:22 CEST Andre Joost wrote:

>> Thanks, that worked for me in this way:
>>
>> cct -z 0 +proj=helmert +convention=coordinate_frame +x=239228.435
>> +y=6693404.951 +s=1.0003267 +theta=18795.4443 <HelmertIn.txt
>>
>>   >>HelmertOut.txt
>>
>
>> Maybe this example should be added to the Helmert and/or cct man pages.
>>
>
> Where do those figures come from ? Is it some official transformation
> registered somewhere ?
>

See 
https://gis.stackexchange.com/questions/300219/helmert-transformation 
and 
http://www.maanmittauslaitos.fi/sites/default/files/Finnish_Coordinate_Systems.pdf, 
chapter 6.2

Seems they have 2D helmert transformations defined between KKJ and 
ETRS-TM35 within every triangulation triangle. The link given in the 
document is not valid anymore, but now available on
 http://coordtrans.fgi.fi/kkj_EUREF-FIN.jsp after login.

One other thing that strikes me:
I have 8 lines within my input file, but only the first 7 get 
transformed. The last input line does not end with CR LF.

No difference if I use
cct -z 0 -o cctout.txt +proj=helmert +convention=coordinate_frame 
+x=239228.435 +y=6693404.951 +s=1.0003267 +theta=18795.4443 Helmertin.txt

cs2cs behaves correctly in this respect, all 8 lines transformed.
So I have to end my file with a blank line to get all points with both 
apps. Tested only on Windows 7.

Greetings,
Andre Joost