[OSM-talk] Help to import Rio de Janeiro city data to OSM - misaligned shapefiles

[Aun Johnsen]

And if you really going to do this complicated, than add that the
earth really is a liquid ball with hard shell pieces, some seismic
events can make the earth wobble which might result in these drifts to
accelerate or delay a few years each, sometimes in different
directions, making these predictable movements somewhat unpredictable.

But all of this is really drifting off topic from the original
questions, how to solve the datum differences in importing data
sources

2010/5/14 John Smith <deltafoxtrot256 at gmail.com>:
> 2010/5/15 Iván Sánchez Ortega <ivan at sanchezortega.es>:
>> Problem is, the center of mass moves along with the continental drift. Have
>> you heard of gravimetrics? You can have looooots of fun with it.
>
> Yes I know, but I was outlining the basic reason why most co-ords on
> most plates shifted 50-200m (or more) when governments started
> shifting to mass centric models.
>
> Also, even though most countries shifted to mass centric based
> systems, they still using plate fixed models that drift from the GPS
> system, in the case of DGA94, by about 7cm NNE on average per year,
> but the plate isn't moving that much, since GPS uses the equator and
> the 0 degree longitude as fixed reference points which also move,
> although different parts of different plates move at different speeds
> and in different directions.
>
> So as you said lots of fun to be had by all if you want to get into it :)
>
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