[Qgis-user] QGIS unable to overlay data with OTF CRS transformations

[Nicolas Cadieux]

Hi, 
The easiest way for now is to simply save the layer in the other CRS ( "save as" and reproject the file) so that both have the same CRS.  Then, you don't need to use OTF. 
Ultimately, a fix for OTF would be best but I believe, complicated from what I have read as this relies, If I understand correctly, on libraries external to QGIS. 
Nicolas 
On Jul 18, 2016 00:58, "Brent Wood-2 [via OSGeo.org]" <ml-node+s1560n5276801h92 at n6.nabble.com> wrote: 

	Hi, I have a dataset in EPSG:4326 which is a 0-360 degree longitude space (which EPSG tells me is a valid use of this projection). I also have one in EPSG:3994 (Mercator 41). QGIS cannot correctly display both of these together in a single map. If I use a project CRS of EPSG:4326 the initial dataset renders correctly, but the EPSG:3994 dataset breaks at 180 degrees. If I use a project CRS of EPSG:3994, then the situation is reversed. The fundamental issue is a discontinuity at 180 degrees longitude. Most lat/long datasets I use around 180 (most of what I do) are 0-360 so they natively plot correctly. I'm not discussing the issues of polygons across 180 (& 0) degrees longitude - this is a more complex issue. Points & lines, however are more straightforward (Ha!) There is a Postgis function ST_Shift_Longitude() which toggles between +-180 & 0-360 longitude spaces for coords in the W hemisphere. An ideal solution would perhaps be to have a similar user specified toggle in QGIS for datasets (or projects) with units degrees, to switch the applied (as opposed to recorded) X coordinate between these. This would allow the EPSG:4326 dataset to be switched to a +-180 space before the coords are sent to Proj for transforming, & the EPSG:3994 dataset to be presented in a 0-360 space in a project using the EPSG:4326 CRS. I've no idea how difficult this might be to implement, possibly a pretty fundamental paradigm shift in how coordinates & CRS's are managed... but it would be nice if QGIS was one of the first GIS tools to start addressing this issue :-) Any comments/suggestions as to how this issue could best be addressed? Thanks,   Brent Wood _______________________________________________
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