[Proj] Understanding 2D Helmert

Andre Joost andre+joost at nurfuerspam.de
Sat Oct 27 03:00:17 EST 2018

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 ?

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.

Andre Joost

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