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

[Brent Wood]

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-user/attachments/20160718/10427fe0/attachment.html>