[gdal-dev] Support for coordinate epoch of dynamic CRS

[Even Rouault]

Hi,

for those not actively tracking github pull requests, I wanted to point
at https://github.com/OSGeo/gdal/pull/3810 which adds initial support
for coordinate epoch of dynamic CRS. You might want to start by reading
https://github.com/rouault/gdal/blob/coordinate_epoch/gdal/doc/source/user/coordinate_epoch.rst

Even

[Greg Troxel]

Post by Even Rouault
https://github.com/rouault/gdal/blob/coordinate_epoch/gdal/doc/source/user/coordinate_epoch.rst
The :cpp:func:`OGRSpatialReference::SetCoordinateEpoch` and
:cpp:func:`OGRSpatialReference::GetCoordinateEpoch` methods can be
used to set/retrieve a coordinate epoch associated with a
CRS. Pedantically the coordinate epoch of an observation belongs to
the observation, and not to the CRS, however it is often more
practical to bind it to the CRS.

There's a lot behind this and it might be helpful to expand. Suggested
text:

Formally, the coordinate epoch of an observation belongs to the
observation. However, almost all formats do not allow for storing
per-observation epoch, and typical usage is a set of observations with
the same epoch. Therefore we store the epoch as property of the CRS,
and the meaning of this is as if that epoch value were part of every
observation. This choice eases processing, storage and format
complexity for most usage. For now, this means that a dataset where
points have different epochs cannot be handled.


I can imagine a table of point features where points in general have a
different epoch. Probably most people would have the reaction "don't go
there" and I would concur this is best avoided, but it's not clear that
it always will be avoidable. Extending per-point storage from xyz to
xyzt feels like a separate activity.

[Even Rouault]

I've formalized that work as a RFC : https://github.com/OSGeo/gdal/pull/3827

Post by Even Rouault
Hi,
for those not actively tracking github pull requests, I wanted to
point at https://github.com/OSGeo/gdal/pull/3810 which adds initial
support for coordinate epoch of dynamic CRS. You might want to start
by reading
https://github.com/rouault/gdal/blob/coordinate_epoch/gdal/doc/source/user/coordinate_epoch.rst
Even

[Nyall Dawson]

Post by Even Rouault
I've formalized that work as a RFC : https://github.com/OSGeo/gdal/pull/3827

Post by Even Rouault
Hi,
for those not actively tracking github pull requests, I wanted to
point at https://github.com/OSGeo/gdal/pull/3810 which adds initial
support for coordinate epoch of dynamic CRS. You might want to start
by reading
https://github.com/rouault/gdal/blob/coordinate_epoch/gdal/doc/source/user/coordinate_epoch.rst

I'm in favour of the proposal and the changes introduced in the
associated PR. There's a very long road ahead of the whole spatial
community (both proprietary and open source) before we can properly
support dynamic CRSes, but this is a step forward in the right
direction.

Thanks for your hard work and initiative in this regards Even!

Nyall