Richard Duivenvoorde <rdmaili...@duif.net> writes: > I think we should never copy the characters, only numbers ( well, > except when using W/S/E/N :-) )..
Having thought a bit more this seems very tricky. > I also understood from somebody that when using latlon coordinates the > minus sign is actually redundant, as you should use the WSEN? I don't think it's that simple, and looking at EPSG I'm sure it's not! (qgis should not be tied to EPSG; it should follow any defined CRS, custom or proj-provided but I understand most are from EPSG.) Sometimes people write any of the following (42, -71) (-71, 42) 42N 71W for geographic. And sometimes DM, DMS. If we are going to try to align with EPSG:4326, I think that means the first form. But looking at https://epsg.org/crs_4326/WGS-84.html it says that the parameter is in degrees [supplier to define representation], and that latitude it positive north, longitude positive east. Degrees are given as https://epsg.org/unit_9122/degree-supplier-to-define-representation.html which means that formally, we must define a representation among the example choices of decimal, DMSH. Other degree formats are just numbers and numbers with hemispheres: https://epsg.org/unit_9102/degree.html https://epsg.org/unit_9116/degree-hemisphere.html So I guess that means qgis could choose any of D DH DM DMH DMS DMSH where H means no negative sign and N/S E/W, lack of H means numbers that could be negative and no N/S/E/W. It is pretty obvious which representation is chosen by how it's printed. It's clear that for cut/paste for computer use, 42,-71 is best, and for human use it depends. Looking beyond WGS84, I picked ITRF2014 and that is also EPSG:9122 (which I find surprising): https://epsg.org/crs_7912/ITRF2014.html >> Part of the underlying trouble is that in qgis/proj we blur: >> datum >> projection >> into >> CRS >> except that some CRS are datum only, and some are datum+projection. > > But isn't that the 'difference' in what QGIS (in the CRS dialog) calls > 'Geographic Coordinate Systems' vs 'Projected Coordinate Systems'? Yes, but in opening a project and clicking around this is really not obvious. I know which are which, but it's really subtle. Someone commented about in US usage Northing preceding Easting, and I think meant for UTM, but might have also meant for State Plane Coordinates. I just checked a survey plan (MA SPC Mainland, which is LCC) and sure enough N is given before E. That doesn't mean it's right in all cases; GIS, geodesy, surveying are all distinct subcultures. Looking up Mass SPC, I find: https://epsg.org/crs_6491/NAD83-2011-Massachusetts-Mainland.html and that is clear: Cartesian 2D CS. Axes: easting, northing (X,Y). Orientations: east, north. UoM: m. which means easting has to come first, and the use of E and N is non-compliant with the EPSG definition. Use of E/N to label those also is fundamentally different than N/S in latitude: it's a label for whcih coordinate is which, not a replacement for a sign bit. My impression is that while people often write xxx.xxxN, xxx.xxxE, it is always easting, northing when used as a coordinate in a machine-readable way. > So: that would make (?): if crs.isGeographic() [0] we should/could use > WSEN, and if not then we should NOT use WSEN (and optionally x/y if > that is more clear)... except when copying coordinates, because that > would mess up parsers :-) It comes back to the purpose of this. I would say: - By default the rules in the CRS should be followed. That means N/S can be used only if the underlying degree reference is EPSG:9122. But then it's optional. - Copy coordinate is intended to produce something machine-readable. That means just numbers, to the extent that is reasonable. - The display format should match what is copied, to follow the Principle of Least Astonishment. - If someone wants a richer display of coordinates in many formats, that should perhaps be another right-click menu item. My vote is for just numbers, like we have now, so the only thing changing is making the axes compliant with the CRS definition. And, perhaps either a preference to select a degree represenation (6 choices!), or multiple entries in the menu. But default should be plain decimal degrees, IMHO. I would be ok with the chosen degree representation being used even if the CRS specifies 9102 instead of 9122. I would also be ok with a preference to add E/N letters to coordinates that are defined to mean Easting and Northing by the CRS. Default off. Hope this helps....
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