From 29a59cadb9d1371479477af517f3431784e880f9 Mon Sep 17 00:00:00 2001 From: Kristian Evers Date: Thu, 14 Feb 2019 12:00:45 +0100 Subject: Reverse direction of deformation operations/transformations/deformation Changed the direction of dt-calculation to follow the same convention as helmert. Changed from dt = t_c - t_obs to dt = t_obs - t_c, which effectively reverses the direction of the operation. Existing projstrings using deformation can simply reverse the direction of the operation to achieve the same results as before this commit. --- docs/source/usage/differences.rst | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) (limited to 'docs/source/usage') diff --git a/docs/source/usage/differences.rst b/docs/source/usage/differences.rst index 5694e4d0..caab865c 100644 --- a/docs/source/usage/differences.rst +++ b/docs/source/usage/differences.rst @@ -69,3 +69,25 @@ Before PROJ 6, the 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` +------------------------------------------------------------------ + +In the initial version of the of :ref:`deformation` operation the time span between :math:`t_{obs}` and :math:`t_c` was determine 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`, 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. -- cgit v1.2.3 From 82855db893dd66de9588497e5748e64a9622ea66 Mon Sep 17 00:00:00 2001 From: Kristian Evers Date: Thu, 14 Feb 2019 12:08:13 +0100 Subject: Cosmetical changes to differences.rst --- docs/source/usage/differences.rst | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'docs/source/usage') diff --git a/docs/source/usage/differences.rst b/docs/source/usage/differences.rst index caab865c..b7c79f53 100644 --- a/docs/source/usage/differences.rst +++ b/docs/source/usage/differences.rst @@ -65,8 +65,8 @@ Version 6.0.0 Removal of proj_def.dat ----------------------- -Before PROJ 6, the 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, +Before PROJ 6, the ``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). -- cgit v1.2.3 From 12689e3d858d66e5e00e8d99f9326ef91cc0a384 Mon Sep 17 00:00:00 2001 From: Kristian Evers Date: Thu, 14 Feb 2019 14:51:39 +0100 Subject: deformation: Replace +t_obs with +dt 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 +dt has been added for that purpose. The new parameter is mutually exclusive with +t_epoch. +dt is used when deformation for a set amount of time is needed and +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. --- docs/source/usage/differences.rst | 27 +++++++++++++++++++++++++-- 1 file changed, 25 insertions(+), 2 deletions(-) (limited to 'docs/source/usage') diff --git a/docs/source/usage/differences.rst b/docs/source/usage/differences.rst index b7c79f53..d5eebe8e 100644 --- a/docs/source/usage/differences.rst +++ b/docs/source/usage/differences.rst @@ -72,8 +72,15 @@ default ellipsoid is GRS80 (was WGS84 in previous PROJ versions). Changes to :ref:`deformation` ------------------------------------------------------------------ +.. _differences_deformation: -In the initial version of the of :ref:`deformation` operation the time span between :math:`t_{obs}` and :math:`t_c` was determine by the expression + +Reversed order of operation +........................... + +In the initial version of the of :ref:`deformation` operation +the time span between :math:`t_{obs}` and :math:`t_c` was determined by the +expression .. math:: @@ -90,4 +97,20 @@ 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. +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. \ No newline at end of file -- cgit v1.2.3