diff options
Diffstat (limited to 'docs/source')
| -rw-r--r-- | docs/source/operations/transformations/deformation.rst | 20 | ||||
| -rw-r--r-- | docs/source/usage/differences.rst | 22 |
2 files changed, 32 insertions, 10 deletions
diff --git a/docs/source/operations/transformations/deformation.rst b/docs/source/operations/transformations/deformation.rst index 87b08453..0a772547 100644 --- a/docs/source/operations/transformations/deformation.rst +++ b/docs/source/operations/transformations/deformation.rst @@ -127,7 +127,7 @@ Mathematically speaking, application of a deformation model is simple. The defor represented as a grid of velocities in three dimensions. Coordinate corrections are applied in cartesian space. For a given coordinate, :math:`(X, Y, Z)`, velocities :math:`(V_X, V_Y, V_Z)` can be interpolated from the gridded model. The time span -between :math:`t_c` and :math:`t_{obs}` determine the magnitude of the coordinate +between :math:`t_{obs}` and :math:`t_c` determine the magnitude of the coordinate correcton as seen in eq. :eq:`apply_velocity` below. .. math:: @@ -144,7 +144,7 @@ correcton as seen in eq. :eq:`apply_velocity` below. Y \\ Z \\ \end{pmatrix}_A + - (t_c - t_{obs}) + (t_{obs} - t_c) \begin{pmatrix} V_X \\ V_Y \\ @@ -154,14 +154,14 @@ correcton as seen in eq. :eq:`apply_velocity` below. Corrections are done in cartesian space. -Coordinates of the gridded model are in ENU (east, north, up) space because it would -otherwise require an enormous 3 dimensional grid to handle the corrections in cartesian -space. Keeping the correction in lat/long space reduces the complexity of the grid -significantly. Consequently though, the input coordinates needs to be converted to -lat/long space when searching for corrections in the grid. This is done with the *cart* -operation. The converted grid corrections can then be applied to the input coordinates -in cartesian space. The conversion from ENU space to cartesian space is done in the -following way: +Coordinates of the gridded model are in ENU (east, north, up) space because it +would otherwise require an enormous 3 dimensional grid to handle the corrections +in cartesian space. Keeping the correction in lat/long space reduces the +complexity of the grid significantly. Consequently though, the input coordinates +needs to be converted to lat/long space when searching for corrections in the +grid. This is done with the :ref:`cart<cart>` operation. The converted grid +corrections can then be applied to the input coordinates in cartesian space. The +conversion from ENU space to cartesian space is done in the following way: .. math:: :label: enu2xyz 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<deformation>` +------------------------------------------------------------------ + +In the initial version of the of :ref:`deformation<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<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. |