Clean up time handling in helmert and deformation #1264
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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.
rouault
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rouault
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Doc: fix example whith used the +t_obs parameter of Helmert removed per #1264
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Previous to this PR both
helmertanddeformationand had+t_obsparameters. They are removed with this PR. Removed fromhelmertbecause it never worked (described in #1239) and indeformationbecause it was potentially confusing. Indeformation+t_obshas been replaced with+dtwhich allow users to specifiy a time-span directly instead of having to set both+t_epochand+t_obs.Additionally the
dtconvention has been changed indeformationfromt_central-t_obstot_obs-t_centralso that it follows the same conventions as used inhelmert(further described in #1242).Closes #1239
Closes #1242