[PROJ] Newbie cs2cs question

[henning at kaarta.com]

Hi all,

New to PROJ, using 7.1.1 on linux, still trying to learn the basics.

 

So it seems to me that one should get the same results from

cs2cs +init=<crs1> +to +init=<crs2> | cs2cs +init=<crs2> +to +init=<crs3>

as

cs2cs +init=<crs1> +to +init=<crs3>

 

i.e. a transform to an intermediate CRS shouldn't affect the final result,
but it seems in my case at least it does. 

E.g.

 

cs2cs -d 6 +init=epsg:4326 +to +init=epsg:7856+5711

151 -33 5

313152.777214   6346936.495810 -20.742001

 

vs.

 

cs2cs -d 6 +init=epsg:4326 +to +init=epsg:32756 | cs2cs -d 6
+init=epsg:32756 +to +init=epsg:7856+5711

151 -33 5

313153.271255   6346937.914960 -20.853001

 

Close, but off by about 1.7m. How would I know which one is correct, and why
are they different?

I must be missing something.thanks!

 

 

 



-- 
This email has been checked for viruses by AVG.
https://www.avg.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/proj/attachments/20200904/429b2417/attachment.html>