and_viceversa

With a dual band survey grade receiver, WGS84 coordinates can be derived to 2cm accuracy in the vertical [0] and even better in the horizontal.

WGS 84 is a time dependent datum - each addition to the ensemble is known as a realization. The software used to convert across time and reference frames is called HTDP [1]. This can also be done for the vertical using VDatum, which wraps HTDP.

The confusion around this issue usually has to do with how analysts actually handle coordinate information in software. For example ESRI, arguably the dominant GIS, does not have time dependent conversion capability. In the US there is also a false equivalence that NAD83 == WGS84. Looks like NZ has a similar issue [2].

Developers also have to deal with this issue, since web mercator and the tiling scheme were designed for convenience and not sub meter accuracy.

[0] https://www.ngs.noaa.gov/PUBS_LIB/NGS592008069FINAL2.pdf [1] https://www.ngs.noaa.gov/TOOLS/Htdp/Htdp.shtml [2] https://www.linz.govt.nz/data/geodetic-system/datums-project...

For a U.S. analog, we use the State Plane system. The states have (multiple) custom projections to suit local accuracy needs. Like another commenter said, WGS 84 uses ellipsoidal coordinates that are not suitable for the Crossrail's construction. If it were really so easy, American states would "just use WGS 84" as well.

After more than a decade of lurking HN... this is the comment that compels me to create an account.

Schwab dropped this ball and left me in the Guatemalan jungle for 18 days after many assurances that they would definitely not send the new card to my home address. Embassy? Nope. Hotel? Impossible. But sure enough it reached my house. Schwab was great, but this was too much.