sp/rgdal workflows with PROJ >= 6 and GDAL >= 3

A description of the status now with regard to a prototype resolution is
online at:

https://rsbivand.github.io/ECS530_h19/ECS530_III.html

I'm planning to stream a talk about this at 09:15-11:00 CET on Tuesday 3
December. I need a volunteer to test the streaming link in advance during
next week. I'm unsure which technology to use for remote participants to
provide feedback.

Contributions/comments welcome!

Roger


On Fri, 15 Nov 2019, Roger Bivand wrote:

The development version of rgdal on R-Forge is now at rev 894, and is

now

ready for trying out with PROJ6/GDAL3 workflows, and workflows that may
migrate within 6 months to modern CRS representations. The motivating

RFC is

also updated to cover coordinate operations, the use of prepared
(pre-searched) coordinate operations, and should be read carefully by

anyone

using rgdal::spTransform(). Note further that rgdal::project() will not

be

adapted for PROJ6, and is effectively deprecated.

I'll be running reverse dependency checks, and may be bugging package
maintainers. I would really prefer that mainainers of packages using
spTransform() checked themselves and joined this thread or the

associated

twitter thread:

https://twitter.com/RogerBivand/status/1194586193108914177

Be ready for modern PROJ and GDAL, they are already being deployed

across

open source geospatial software, like GRASS, QGIS, pyproj, spatialite

etc.

Waiting, hopefully not in vain, for contributions.

Roger

On Wed, 13 Nov 2019, Roger Bivand wrote:

 And this link explains the CDN proposal for grid distribution:

 https://www.spatialys.com/en/crowdfunding/

 Roger

 On Wed, 13 Nov 2019, Roger Bivand wrote:

  Because PROJ >= 6 and GDAL >= 3 change the way that PROJ strings
  (representations of coordinate reference systems) are handled, steps

are

  being taken to find ways to adapt sp/rgdal workflows. A current

proposal

  is to store the WKT2_2018 string as a comment to CRS objects as

defined

  in
  the sp package.

  A draft development-in-progress version of rgdal is available at
  https://r-forge.r-project.org/R/?group_id=884, and for sp at
  https://github.com/rsbivand/sp (this version of sp requires rgdal >=
  1.5-1). This adds the WKT comments to CRS objects on reading vector

and

  raster data sources, and uses WKT comments if found when writing

vector

  and raster objects (or at least does as far as I've checked, possibly
  fragile).

  An RFC with tersely worked cases for using CRS object comments to

carry

  WKT strings but maintaining full backward compatibility is online at
  http://rgdal.r-forge.r-project.org/articles/PROJ6_GDAL3.html.

  If you have other ideas or concerns about trying to use this

mechanism

  for
  sp CRS objects, please contribute at your earliest convenience.

  http://rgdal.r-forge.r-project.org/reference/list_coordOps.html

shows

  the
  beginning of the next step, to query transformation operations to

find

  viable coordinate operation pipelines.

  I'm assuming that the previous behaviour (transform without

considering

  accuracy with whatever is to hand) is not viable going forward, and

that

  we will need two steps: list coordinate operations between source and
  target CRS (using the WKT comments as better specifications than the
  PROJ
  strings), possibly intervene manually to install missing grids, then
  undertake the coordinate operation.

  The fallback may be simply to choose the least inaccurate available
  coordinate operation, but this should be a fallback. This means that

all

  uses of spTransform() will require intervention.

  Is this OK (it is tiresome but modernises workflows once), or is it

not

  OK
  (no user intervention is crucial)?

  These behaviours may be set in an option, so that package maintainers
  and
  users may delay modernisation, but all are undoubtedly served by

rapid

  adaptation (GRASS 7.8.1 released yesterday, libspatialite, pyproj,

QGIS

  development versions all state that they list candidate coordinate
  operations).

  We cannot ship all the grids, they are very bulky, and probably

nobody

  needs sub-metre accuracy world-wide. Work in PROJ is starting to

create

  a
  content delivery network for trusted download and mechanisms for
  registering downloaded grids on user platforms. We would for example

not

  want Windows users of rgdal and sf to have to download the same grid
  twice.

  Comments welcome here and at
  https://github.com/r-spatial/discuss/issues/28 or
  https://github.com/r-spatial/sf/issues/1187

  Roger

--
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; e-mail: Roger.Bivand at nhh.no
https://orcid.org/0000-0003-2392-6140
https://scholar.google.no/citations?user=AWeghB0AAAAJ&hl=en