# Known differences between versions¶

Once in a while, a new version of PROJ causes changes in the existing behaviour. In this section we track deliberate changes to PROJ that break from previous behaviour. Most times that will be caused by a bug fix. Unfortunately, some bugs have existed for so long that their faulty behaviour is relied upon by software that uses PROJ.

Behavioural changes caused by new bugs are not tracked here, as they should be fixed in later versions of PROJ.

## Version 4.6.0¶

The default datum application behavior changed with the 4.6.0 release. PROJ will now only apply a datum shift if both the source and destination coordinate system have valid datum shift information.

The PROJ 4.6.0 Release Notes states

MAJOR: Rework pj_transform() to avoid applying ellipsoid to ellipsoid transformations as a datum shift when no datum info is available.

## Version 5.0.0¶

### Longitude wrapping when using custom central meridian¶

By default PROJ wraps output longitudes in the range -180 to 180. Previous to PROJ 5, this was handled incorrectly when a custom central meridian was set with +lon_0. This caused a change in sign on the resulting easting as seen below:

$proj +proj=merc +lon_0=110 -70 0 -20037508.34 0.00 290 0 20037508.34 0.00  From PROJ 5 on onwards, the same input now results in same coordinates, as seen from the example below where PROJ 5 is used: $ proj +proj=merc +lon_0=110
-70 0
-20037508.34    0.00
290 0
-20037508.34    0.00


The change is made on the basis that $$\lambda=290^{\circ}$$ is a full rotation of the circle larger than $$\lambda=-70^{\circ}$$ and hence should return the same output for both.

Adding the +over flag to the projection definition provides the old behaviour.