[chrismorgan]

This is how things are done. You specify the datum, coordinates, and time. Geodetic datums are time-dependent transformation functions. Any software that is recording points at the particular time called “now” and not either recording the coordinates and time, or reprojecting them to a meaningful reference datum at its epoch (origin in time), is bad.

[amluto]

As far as I can tell, GIS software is bad, then. I spent longer than seemed at all reasonable trying to research this with QGIS, and I got nowhere. ArcGIS (which I don’t have) wasn’t obviously better.

Do you have an example of good software?

[chrismorgan]

Sorry, no. This was my dad’s field, not mine, so I’ve just got a bunch of second-hand info and know that the software he worked on (two pieces, one for a company and one of his own) handled these sorts of things correctly. And I find it genuinely impossible to imagine that major GIS software would not handle this, because it’s so fundamental.

Your GIS software will have you set a base CRS, and then, presuming it’s not recording time on points, all coordinates will be relative to it at its epoch. That’s all you need, now if you want to see what it’s like now, you project it accordingly. Anything along the lines of recording new points based on actual measurements should obviously either record time and position, or just position after performing the reverse transformation. But there you’d tend to be getting beyond the domain of what the bulky GIS software is doing, and into the domain of specific-purpose mobile apps and such.