[Proj] HTPD

Kristian Evers kristianevers at gmail.com
Wed Feb 28 14:39:09 EST 2018

Hi Duncan, 

There’s clearly more to HTPD than I had realized. From what you describe it is
definitely useful to American PROJ users. The modelling of displacement after seismic events is not
something we can do in a smart way in PROJ, so HTPD can not be replaced by PROJ. Yet anyway :-)

The current doc page, however, is still primarily documenting a tool from GDAL, which ideally would be
taken care of in the GDAL docs. For now I’ll keep the information in the PROJ docs as well although in a less
prominent space (somewhere in the grids-section instead of a chapter by itself).

Thanks for your feedback.


> On 28 Feb 2018, at 19:49, Duncan Agnew <dagnew at ucsd.edu> wrote:
> Kristian:
> If I understand the material about deformation grids correctly (and I may not) these describe velocities only.
> HTDP includes velocities, but also the episodic deformation associated with earthquakes: which earthquakes
> of course depends on the two time epochs. This could all be done using the pipeline system by providing
> displacement grids for each earthquake, though the user would have to chose which ones to chain together.
> HDTP hides all these complications, in keeping with its original goal of providing an easily-used black box
> for surveyors who had data from a number of different epochs. Initially it was intended for use only for
> California and environs, though over the years it has been extended--I see that It now includes postglacial
> rebound for the Eastern US.
> But if there is a way to provide the same functionality without HTDP I can see that this would be cleaner.
> Thanks
> Duncan Agnew
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