[Proj] Offset when converting coordinates from ESRI:31700 to EPSG:4326

Mikael Rittri Mikael.Rittri at carmenta.com
Mon May 2 03:55:01 EST 2011


Hello Adrian.

First a minor point: sterea is better than stere
(at least for Romania, the Netherlands and Canada)
as you mentioned in your first post, so I think
using +init=epsg:31700 is better than +init=esri:31700, 
since only the epsg definition gives sterea, also 
according to you first post.  (In the Netherlands,
I think the difference between stere and sterea can
be up to 7 or 8 meters.)

Second, you have added a +towgs84 parameter, but 
omitted the +to and what comes after.  However, 
the +towgs84 is not a replacement for the +to etc., 
just additional information. 
(In fact, a +towgs84 parameter is often needed on 
 both sides of the +to separator. I'm surprised
 that cs2cs gives any output at all without any 
 +to separator.)

I tried the following:

C:\Program Files\FWTools2.4.7>echo 587486.770 326878.452 | cs2cs +init=epsg:31700 +towgs84=2.329,-147.042,-92.08,-0.309,0.325,0.497,5.69 +to +init=epsg:4326 -f '%0.6f'
'26.097437'     '44.436336' '36.350887'

You wrote:

> Real coordinates (converted from Stereo 70 with Global Mapper 
> and checked with a GPS unit): 26.097414, 44.436335

So the error is now 1.8 meters for this example 
(measured on http://geographiclib.sourceforge.net/cgi-bin/Geod),
which is what one could expect (since the horizontal accuracy
of this datum shift is supposed to be 1.5 to 3 meters).

Best regards,

Mikael Rittri
Carmenta
Sweden
http://www.carmenta.com


-----Original Message-----
From: Adrian Popa [mailto:adrian_gh.popa at romtelecom.ro] 
Sent: den 2 maj 2011 10:03
To: Mikael Rittri
Cc: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] Offset when converting coordinates from ESRI:31700 to EPSG:4326

Hello everyone,

First of all - thank you all for the information provided (and sorry I didn't reply sooner).

Second of all - I still must be doing something wrong - the coordinates I get are the same in all cases (the same as EPSG 4326):

adrianp at frost:~$ echo 587486.770 326878.452 | cs2cs +init=esri:31700 +to
+init=epsg:4326 -f '%0.6f'
26.099032    44.436575 0.000000
adrianp at frost:~$ echo 587486.770 326878.452 | cs2cs +init=esri:31700
+towgs84=28,-121,-77 -f '%0.6f'
26.099032    44.436575 0.000000
adrianp at frost:~$ echo 587486.770 326878.452 | cs2cs +init=esri:31700
+towgs84=44.107,-116.150,-54.648 -f '%0.6f'
26.099032    44.436575 0.000000
adrianp at frost:~$ echo 587486.770 326878.452 | cs2cs +init=esri:31700
+towgs84=-5.20,-126.75,-97.08,0.3160,0.4470,0.1340,0.99999  -f '%0.6f'
26.099032    44.436575 0.000000
adrianp at frost:~$ echo 587486.770 326878.452 | cs2cs +init=esri:31700
+towgs84=2.329,-147.042,-92.08,-0.309,0.325,0.497,5.69   -f '%0.6f'
26.099032    44.436575 0.000000

I'm sorry, but I'm a complete noob to proj and I do not understand the full theory behind projections, datums and all the rest - so I hope my questions are not too irritating :)

So - any clue to what I'm doing wrong?
Thank you,

Adrian


Acest mesaj si orice fisiere sau documente atasate contin informatii confidentiale, clasificate conform regulilor interne ROMTELECOM. Mesajul este destinat doar persoanei sau entitatii adresate si altora autorizati sa-l primeasca. Daca dvs. nu sunteti in aceasta situatie, prin aceasta va informam ca orice dezvaluire, copiere, distribuire sau orice alta actiune bazata pe continutul acestor informatii este strict interzisa si pot fi aplicate sanctiuni, potrivit legii. Daca ati primit acest mesaj din greseala, va rugam sa ne informati imediat si sa stergeti mesajul din sistemul dvs. De asemenea, va rugam sa tineti cont ca transmisia nu poate fi garantata ca fiind sigura sau fara erori. Va multumim!


More information about the Proj mailing list