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WGS 84 and MSL

WGS 84 and MSL

WGS 84 and MSL

I am working in the middle east. I have got a doubt to clear which is related to WGS 84 and MSL heights. Here in our project the WGS84 datum is used as reference only for the X and Y and the scale factor is used for them, and for Z following the local MSL which is given by the National Survey authority, by means of a set of Benchmarks. Is it a non-conventional survey system?
Actually when a third party involved in the survey, they claimed that, they followed WGS84 datum, and so do the elevations of the benchmarks were differed by max. 100mm when it is measured from east to west. So my concern is what is actually the difference? Is there anything really wrong when we are following the MSL. And WGS84 heights can not be conncected with a level machine, which we tried at site and observed. So are the WGS84 heights really usable, where we need a precision of +/-5mm? how do i prove that this system doesn't make any adverse implications, and it is not wrong?! How are the GPS heights been calculated, are they the orthometric heights? Please help!



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