Jochem Kail via QGIS-User <[email protected]> writes: >> It is a major problem in GIS that data are mislabeled as being in WGS84 >> and that it is treated as an interchange format. Both practices are >> errors, but also the standard approach. > > In summary, I now do suspect, that the data from 2011 were mislabeled > as being WGS84. Based on what I do understand so far, the ITRF > reference frame in 2011 was ITRF2000, which corresponds to the WGS 84 > (G1150) realization. However, most likely the RTK network has been > used as reference stations. Therefore, the geographic coordinates are > most likely based on the ETRS89 reference system (not WGS84) and given > that the data have been mapped in 2011, based on the ETRF realization > ETRF2000.
You said "DGPS" earlier and now you are saying "RTK". These are not the same thing. To get this right, you need to be clear on what was done before, from what reference station, and what CRS that reference station was operating in. That should have been collected as source metadata at the time, and the proper CRS label applied to the dataset, which is easier said than done, to fix in hindsight. The idea that a DGPS (or RTK) network in Europe, in 2011, was in ETRF2000, is highly plausible More or less, surveying (that uses beyond-site coordinates) and national mapping activities very strongly tend to use the national/regional datum. Further, in the US, while we use "NAD83(2011)", networks are all set up for the 2010.0 epoch of that (technically dynamic) datum, even today. I am unclear on EU practice in this regard. It remains a fair, if probably unimportant, question to ask whether the DGPS/RTK base station reference coordinates were in ETRF2000 epoch 1989.0 or in some different epoch. The point of ETRS is to be plate fixed, and thus velocities of points on the ground, when expressed in ETRF2000, should be near zero. At 1 mm/y, we're talking 15 mm, and at 1 cm/y, it's 15 cm. > No I am still struggeling to find a way to do a time-dependent > transformation in QGIS from ETRS89/ETRF2000 to the recent > ETRS89/ETRF2020. You are writing ETRS89/ETRF2000 as if it is a compound object, which it isn't. ETRS89 is a "system", which gives rules for defining frames, so there are no cooprdinates in ETRS89. ETRF2000 is a "realization" of the system, also called a datum or reference frame. I am unaware of people treating ETRFxxxx as dynamic, even though it technically seems defined that way. But I am underclued about ETRS/ETRF practices. I would suggest that you relabel your 2011 data as being in ETRF2000 and see what happens. Also use command-line proj: $ projinfo -s ETRF2000 -t ETRF2020 which returns a lot of operations that surprise me, being time-dependent transforms with non-zero rates (despite both ETRF2000 and ETRF2020 both having base epoch of 1989.0). But I say again, I am underclued about ETRS. _______________________________________________ QGIS-User mailing list [email protected] List info: https://lists.osgeo.org/mailman/listinfo/qgis-user Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
