[Qgis-user] QGIS GNSS NMEA Transformation Problem WGS84 to MGI Austria

[Peter Hartl]

Thanks Greg,

QGIS interprets NMEA data as WGS84 geographic data which is correct!
I could not find to say to QGIS that it should use ETRS89 datum!

We are using *QField*, here Transformation in X, Y from GNNS into our 
MGI with gridshift is working correkt (Vertical girdshift works too very 
goo in cm accuracy)!

The *same QGIS projekt behind with QGIS* shows data in map correct (set 
to 25832) but in saving to 31254 it gets shift, without possibiltity for 
changing that for me.

For me it looks like a issue in QGIS!

Herzliche Grüße

Hartl Consulting e. U.
DI Peter Hartl MAS(GIS)
Gröben 11
A-6134 Vomp
Tel.: +43 660 17 42 228

office at hartl-consulting.at
www.hartl-consulting.at

Am 07.02.2025 um 14:51 schrieb Peter Hartl via QGIS-User:
> Hallo Greg,
>
> thanks for Information, will check NMEA RTK data in detail first.
>
> Greetings
> Peter Hartl
>
> Von meinem iPhone gesendet
>
>> Am 07.02.2025 um 13:22 schrieb Greg Troxel via QGIS-User<qgis-user at lists.osgeo.org>:
>>
>> Peter Hartl via QGIS-User<qgis-user at lists.osgeo.org> writes:
>>
>>> GNSS NMEA interpreted as WGS84 in QGIS can do transformation with
>>> gridshift from ETRS89 to MGI, that is alredy working very good.
>> What do you mean by "GNSS NMEA interpreted as WGS84"?  What reference
>> frame is your GNSS data actually in?   It could be
>>
>>   WGS84(G2159) if you are using a non-differential solution
>>
>>   ITRF? if you are using SBAS
>>
>>   ETRF? if you are using some RTK network
>>
>>   something else, if your receiver  is combining 4 constellations, each
>>   of which have their own frames, and doing something that they don't
>>   document (hint: I have never seen any receiver document this.)
>>
>>
>> You should be aware that WGS84 is an ensemble, which means that when you
>> say data is in WGS84 that it is in one of several datums, and you don't
>> know which one.
>>
>> The inherent accuracy limitation of the ensemble is about 2m.   So
>> therefore a shift of 30 cm is not wrong.
>>
>>
>> Probably, it would be good to figure out how to not use WGS84,
>> especially if you are tryig to work at sub-meter accuracy.    I have
>> done this by gathering data in NAD83(2011) epoch 2010.0, which is more
>> plate fixed, more or less analagous to ETRS89, using RTK with a
>> reference network operating in NAD83.
>>
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