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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 tim

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 https://www.ngs.noaa.gov/PUBS_LIB/NGS592008069FINAL2.pdf [1] https://www.ngs.noaa.gov/TOOLS/Htdp/Htdp.shtml https://www.ngs.noaa.gov/TOOLS/Htdp/Htdp.shtml [2] https://www.linz.govt.nz/data/geodetic-system/datums-projections-and-heights/geodetic-datums/world-geodetic-system-1984-wgs84 https://www.linz.govt.nz/data/geodetic-system/datums-project...

teruakohatu 4y ago
> 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. Accuracy or precision? The issue is accuracy, not precision. > Developers also have to deal with this issue, since web mercator and the tiling scheme were designed for convenience and not sub meter accuracy. This is a projection problem. All projections are essentially wrong, and tradeoffs need to be made (eg. you can't flatten an orange on a desk without distorting some parts of it) . Unfortunately users don't understand this which is why people get excited when they discover America is smaller, and Africa larger, than they thought. Ideally when zooming into a country a more suitable projection would be used, but at the end of the day it doesn't matter much for consumers. I think software developers don't give GIS developers enough credit. Software devs will endless debate and be critical of floating point issues, but also not consult with a GIS professional when doing spatial work. People don't know what they don't know.

teruakohatu 4y ago

> 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. Accuracy or precision? The issue is accuracy, not precision. > Developers also have to deal with this issue, since web mercator and the tiling scheme were designed for convenience and not sub meter accuracy. This is a projection problem. All projections are essentially wrong, and tradeoffs need to be made (eg. you can't flatten an orange on a desk without distorting some parts of it) . Unfortunately users don't understand this which is why people get excited when they discover America is smaller, and Africa larger, than they thought. Ideally when zooming into a country a more suitable projection would be used, but at the end of the day it doesn't matter much for consumers. I think software developers don't give GIS developers enough credit. Software devs will endless debate and be critical of floating point issues, but also not consult with a GIS professional when doing spatial work. People don't know what they don't know.