On Thu, 27 Jun 2019 at 17:40, Richard Duivenvoorde <rdmaili...@duif.net> wrote: > > Hi, > > Starting up a fresh 3.8 and loading a EPSG:28992 (our national crs) > layer I got a dialog questioning me which Transformation to use.
Looks like something/someone has changed a setting on your QGIS. (Options - CRS - "Ask for datum transformation if several are available"). The default is off. > I wrote something down here: > > http://www.qgis.nl/2019/06/27/english-proj-select-datum-transformations-for-epsg28992/?lang=en > > Question to devs: what is the meaning of the 'green' item in this > dialog? It's just the first, non-deprecated one. I.e. - more or less random. On proj < 6.1 builds treat any transformations with great suspicion. > Is it the old one? Or a default one? > Because reading the texts there, it appears that the last item is to be > used? Well - (don't read this as snark, I'm just trying to accurately convey the situation): if you want to make the correct choice, fire up proj 6.1's projinfo tool and see what it suggest for transforming between the two systems. On QGIS < 3.8 or proj < 6.1, this dialog is using a custom database of "transformations", which was ad hoc, unreliable, and basically untrustworthy. The good news is that the solution is already done -- you just need a QGIS 3.8 build based on Proj 6.1. And then you can trust QGIS' transformation capabilities as being the best there are available anywhere (thanks entirely to the proj team). > Question 2: IF somebody makes a mistake, how do you get this dialog back > to choose another one? The setting is saved in the project properties (or in the options, CRS tab if you clicked "make default"). > Cannot find something in docs or changelog about it (besides: > http://changelog.qgis.org/en/qgis/version/3.8/#much-improved-coordinate-transform-handling) On proj < 6.1 builds none of this is new. It's been cleaned up a bit, and some bugs fixed, but it's been relatively unchanged since 3.0. Nyall > > Hoping that this question and writing this down in a blog will help > others too. > > Regards, > > Richard Duivenvoorde > _______________________________________________ > QGIS-Developer mailing list > QGIS-Developer@lists.osgeo.org > List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer _______________________________________________ QGIS-Developer mailing list QGIS-Developer@lists.osgeo.org List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer