On Mon, 1 Jul 2019 at 16:46, Andreas Neumann <[email protected]> wrote: > > Hi, > > I am wondering about projects without a CRS. While a new project now always > comes with a CRS (depending on the global CRS settings), the user can still > explicitly disable a definition of a CRS in Menu "Project" --> "Properties" > --> "CRS" > > I have the following questions about projects without a CRS: > > - what are the restrictions/limitations of projects without a CRS?
Coordinates are all just treated as "pure numbers". Distance and area measurements are unit-less. Scale values have no real-world meaning. Time and space break down into a singularity where "up" is left and "right" is tuesday, July (and sometimes never). (ok, everything but that last one!) > > - assuming that a layer has a CRS (e.g. a Postgis layer that has a CRS) is > loaded into a project that explictly has no CRS set - does QGIS still know > the CRS of the Postgis layer or would it treat it as a CRS-less layer? It still knows the CRS, and will show it e.g. in layer properties, but the project doesn't do anything with this information. It's still utilised by layer-specific operations though (e.g. saving the layer to another format). > - does it still make sense to support projects without a CRS? If yes, what > are the use cases? Yes, for projects which don't use real-world coordinates. E.g. projects using some local invented coordinate system, buildings, mapping on tiny scales, mapping off-world objects, creating maps of fantasy novels or video game worlds,... > - will it still be possible to have projects without a CRS or will this one > day be deprecated I don't think it should ever be deprecated, there's a demonstrated need for it. > I personally do understand that it is not a good idea to have projects with > no CRS defined, but I am trying to understand and convince my colleagues at > my workplace that projects without a CRS are an absolute nogo. But maybe I am > wrong and it still makes sense to support projects without a CRS. It's basically the same argument required to convince CAD designers to use real world coordinate systems and not just some paper-based reference system. Fortunately, I think that battle has more-or-less been won, so maybe the same arguments can be used here... The other thing to consider is that CRS-less projects are only half the solution. We also should add concepts of CRS-less layers, which, when loaded into a project WITH a CRS set, are still always just treated as raw numbers and not projected in any way. Nyall > One use case I could think of for projects without a CRS, is using QGIS for > something that is planar, but not geographic in nature, e.g. a non-GIS topic, > such as examining an image (let's say the enlarged view of an electron > microscope of some small thing) where the user might want to "map" certain > characteristics of the image, but the object itself is "mobile" (can move > around) and is not fixed to a fixed position of the earth. > > What are your thoughts about projects without a CRS? > > Greetings, > > Andreas > > > _______________________________________________ > QGIS-Developer mailing list > [email protected] > List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer _______________________________________________ QGIS-Developer mailing list [email protected] List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
