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diff --git a/_sources/usage/differences.rst.txt b/_sources/usage/differences.rst.txt new file mode 100644 index 00000000..3bc2f54d --- /dev/null +++ b/_sources/usage/differences.rst.txt @@ -0,0 +1,147 @@ +.. _differences: + +================================================================================ +Known differences between versions +================================================================================ + +Once in a while, a new version of PROJ causes changes in the existing behavior. +In this section we track deliberate changes to PROJ that break from previous +behavior. Most times that will be caused by a bug fix. Unfortunately, some bugs +have existed for so long that their faulty behavior 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 :c:func:`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 +:option:`+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 :math:`\lambda=290^{\circ}` is a full +rotation of the circle larger than :math:`\lambda=-70^{\circ}` and hence +should return the same output for both. + +Adding the ``+over`` flag to the projection definition provides +the old behavior. + +Version 6.0.0 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + +Removal of :file:`proj_def.dat` +------------------------------- + +Before PROJ 6, the :file:`proj_def.dat` was used to provide general and per-projection +parameters, when ``+no_defs`` was not specified. It has now been removed. In case, +no ellipsoid or datum specification is provided in the PROJ string, the +default ellipsoid is GRS80 (was WGS84 in previous PROJ versions). + +Changes to :ref:`deformation<deformation>` +------------------------------------------------------------------ +.. _differences_deformation: + + +Reversed order of operation +........................... + +In the initial version of the of :ref:`deformation<deformation>` operation +the time span between :math:`t_{obs}` and :math:`t_c` was determined by the +expression + +.. math:: + + dt = t_c - t_{obs} + +With version 6.0.0 this has been reversed in order to behave similarly to +the :ref:`Helmert operation<helmert>`, which determines time differences as + +.. math:: + + dt = t_{obs} - t_c + +Effectively this means that the direction of the operation has been reversed, +so that what in PROJ 5 was a forward operation is now an inverse operation and +vice versa. + +Pipelines written for PROJ 5 can be migrated to PROJ 6 by adding :option:`+inv` +to forward steps involving the deformation operation. Similarly +:option:`+inv` should be removed from inverse steps to be compatible with +PROJ 6. + +Removed ``+t_obs`` parameter +............................. + +The ``+t_obs`` parameter was confusing for users since it effectively +overwrote the observation time in input coordinates. To make it more clear +what is the operation is doing, users are now required to directly specify +the time span for which they wish to apply a given deformation. The parameter +:option:`+dt` has been added for that purpose. The new parameter is mutually +exclusive with :option:`+t_epoch`. :option:`+dt` is used when deformation +for a set amount of time is needed and :option:`+t_epoch` is used (in +conjunction with the observation time of the input coordinate) when +deformation from a specific epoch to the observation time is needed. + +Version 6.3.0 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + +projinfo +-------- + +Before PROJ 6.3.0, WKT1:GDAL was implicitly calling ``--boundcrs-to-wgs84``, to +add a ``TOWGS84[]`` node in some cases. This is no longer the case. + + +Version 7.0.0 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + +proj +-------- + +Removed ``-ld`` option from application, since it promoted use of deprecated +parameters like ``+towgs`` and ``+datum``. + +cs2cs +-------- + +Removed ``-ld`` option from application, since it promoted use of deprecated +parameters like ``+towgs`` and ``+datum``. + +UTF-8 adoption +-------------- + +The value of all path, filenames passed to PROJ through function calls, PROJ +strings or environment variables should be encoded in UTF-8. |