[postgis-devel] PostGIS and the new Proj4 transformation pipeline

[Paul Ramsey]

Hey G,
More precise transforms is nice, but reading through your links we seem to
be dropping an awful lot of responsibility onto users laps with regard to
defining the transforms. Can we use the new precision along with a database
of "best transforms" between pairs of systems?
Keeping the relatively simple "from system A to system B" syntax without
adding a third very complicated term "from system A via transform C to
system B" would be good. What's the state-of-the-art in terms of making
selection of the pipeline automagical?
P


On Fri, Sep 15, 2017 at 5:19 AM, G. Allegri <giohappy at gmail.com> wrote:

> Hi,
> during the past days there's been a very interesting discussion within the
> QGIS community [1] about the refactoring of its way of managing CRS
> transformations. Some from Proj4 have joined the conversation to help in
> understanding the newcoming Proj4 feature: transformation pipeline [2] [3].
>
> This is a great and deep enhancement to the capabilities of Proj4, toward
> more complex transformations and, consequently, higher precisions.
>
> The new concept has lead to a new API and a new way to manage
> transformations definitions.
>
> I cross post it here because I find that this should be considered by
> PostGIS too.
> Just for a use case I recently was asked support for: employing grid
> shifts within PostGIS. It's already possible to define a custom CRS with a
> nadgrids parameter, but this suffers WGS84 pivoting, which is the current
> way Proj4 works.
> With the new pipeline it can be circumvente if a specific, straight, CRS
> to CRS transformation is defined.
>
> I hope there will be some interest here to keep this conversation going
> on, looking at adopting the new Proj4 API in the future versions of PostGIS.
>
> All the best,
> Giovanni
>
> [1] https://github.com/qgis/QGIS-Enhancement-Proposals/issues/100
> [2] https://lnkd.in/emzw2HA
> [3] https://kbevers.github.io/usage/transformation.html
>
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