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 
On Jul 18, 2016 00:58, "Brent Wood-2 [via OSGeo.org]" 
<ml-node+s1560n5276801...@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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