[GRASS-dev] PROJ6 support in GRASS

[Markus Metz]

On Wed, Sep 4, 2019 at 6:01 PM Markus Neteler <neteler at osgeo.org> wrote:
>
> On Wed, Sep 4, 2019 at 4:31 AM Anna Petrášová <kratochanna at gmail.com>
wrote:
> > On Tue, Sep 3, 2019 at 4:22 AM Markus Metz <
markus.metz.giswork at gmail.com> wrote:
> >>
> >> Hi all,
> >>
> >> there is a new PR for PROJ6 support in GRASS
> >> https://github.com/OSGeo/grass/pull/118
> >>
> >> There are two important changes when using PROJ6:
> >>
> >> First, reprojection with v.proj and r.proj is no longer always
possible without the user making informed decisions. The reason is that
there can be several different operations available to reproject
coordinates from one CRS to another CRS. These different operations are
listed and the user has to provide the appropriate operation with the
pipeline option, taking care of any axisswap.
> >
> > first, thanks for all the work. Second, I don't see how most users are
supposed to know what to pick. Is there perhaps a way to pick a good
default? I just can't imagine not having r.import/v.import...
>
> I see the same problem: users won't know what to select if defaults
> are gone with PROJ 6.

We can provide information that enables users to make an informed decision.
The options listed by PROJ6 are ordered by guessed best choice, i.e. the
first one is, given the provided information, the best choice. But users
need to review the list of options.

Reprojection from one CRS to another CRS was never easy. For both raster
and vector data, some preparation was always needed to decide on
appropriate settings. PROJ6 provides methods to improve the accuracy of
reprojected coordinates, depending on the actual use case. The user decides
(must decide).
>
> > Anna
> >>
> >>
> >> Second, axis order is no longer always easting, northing, e.g. for
EPSG:4326 it is northing, easting, and an axisswap might need to be removed
from operations provided by PROJ.
> >>
> >> There are many more changes (see details in the PR), but these are the
two most important ones.
> >>
> >> Feedback welcome!
>
> Thanks for your hard work.
>
> I talked to Robert Bivand here at the GeoSTAT 2019 in Münster who gave
> a talk about the topic:
>
> "Not just R-spatial: sustaining open source geospatial software stacks"
> https://github.com/rsbivand/geostat19_talk
>
> You can quick-view the talk in rendered HTML like this (maybe there
> are better ways):
>
http://htmlpreview.github.io/?https://raw.githubusercontent.com/rsbivand/geostat19_talk/master/docs/geostat_bivand_19.html
>
> It contains a section about PROJ (6).

Not so random citation:
"...we need to manipulate the CRS read in with the file to insert our
choice of how to make the transformation..."

I will try to restrict the number of options based on the current region in
a modified PR.

Markus M
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