[Proj] puzzled with +towgs84=... being ignored

Just van den Broecke just at justobjects.nl
Fri Jan 10 05:54:11 EST 2014


I agree with Andre. One remark. Looking at the parameters, I presume you 
try to transform to Dutch, EPSG:28992. Your +towgs84 parms seem have an 
"unusual" value, maybe outdated, or perhaps on purpose. The others are ok.

Your value:

Proj 4.8.0 value:
+towgs84=565.417,50.3319,465.552,-0.398957,0.343988,-1.8774,4.0725 (see 
<28992> entry in http://trac.osgeo.org/proj/browser/trunk/proj/nad/epsg)

I've seen slight differences in, and even omission of, +towgs84 for 
EPSG:28992 here and there, as there has been some confusion over the 
years, but the Proj 4.8.0  value is now settled on (e.g. found in 
PostGIS 2.x as well).


Just van den Broecke
The Netherlands

On 10-01-14 05:55, Andre Joost wrote:
> Am 10.01.2014 01:28, schrieb J. Luis:
>> I'm very lost with this results where setting the +towgs84 is ignored
>> unless I set "+datum=WGS84"
>> Why so? and why is the source "+ellps=WGS84" ignored as well?
> This is the usual behaviour: +towgs84 is only used when a datum shift is
> defined on both sides (from and to), either by specifying
> +datum=...
> +nadgrids=...
> +towgs84=...
> HTH,
> Andre Joost
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