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Clean up time handling in helmert and deformation #1264

merged 5 commits into from
Feb 14, 2019


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@kbevers kbevers commented Feb 14, 2019

Previous to this PR both helmert and deformation and had +t_obs parameters. They are removed with this PR. Removed from helmert because it never worked (described in #1239) and in deformation because it was potentially confusing. In deformation +t_obs has been replaced with +dt which allow users to specifiy a time-span directly instead of having to set both +t_epoch and +t_obs.

Additionally the dt convention has been changed in deformation from t_central-t_obs to t_obs-t_central so that it follows the same conventions as used in helmert (further described in #1242).

Closes #1239
Closes #1242

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.
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.
@kbevers kbevers merged commit a813ad6 into OSGeo:master Feb 14, 2019
@kbevers kbevers deleted the remove-t_obs branch February 14, 2019 18:22
@kbevers kbevers added this to the 6.0.0 milestone Feb 14, 2019
rouault added a commit that referenced this pull request Feb 7, 2022
Doc: fix example whith used the +t_obs parameter of Helmert removed per #1264
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