Am Fr., 8. Mai 2020 um 14:09 Uhr schrieb Greg Troxel <g...@lexort.com>:
> Martin Koppenhoefer <dieterdre...@gmail.com> writes: > > > Am Fr., 8. Mai 2020 um 03:22 Uhr schrieb Greg Troxel <g...@lexort.com>: > > > >> 3) Look up the data sheet and mark it as ele:datum=NGVD29 or > >> ele:datum=NAVD88 as it turns out. > > > > IIRR, in another mail, you wrote that the difference between these 2 is > > less than a meter, can you confirm this, or did I understand you or > > remember wrong? > > Yes,it typically is. > > So let me ask you again, since you keep declining to answer this: > > Please give an example of an elevation of a real thing that is > meaningfully different in one of these "regional datums" (established > by a country's survey agency) compared to WGS84 height above geoid. > Identify the regional datum, and identify two values linked with a > rigorous transformation (such as national survey agencies publish). > > > Thus far, you have not established that there is an actual problem that > needs to be solved. > I was not aware there weren't any meaningful differences (when comparing some official height references to the German DHHN92 those in wikipedia.de with delta information all are within 1m besides Belgium DNG/TAW, which is -2.3). Maybe all we should do is clarify that we are NOT expecting ellipsoid heights in ele tags (leaving open the possibility to add ele:datum tags)? WGS84 uses a 2 dimensional ellipsoidal coordinate system? Wouldn't "natural" height information be based on this ellipsoid? I'm all fine with stating we should use geoid heights, but it doesn't necessarily seem to be implicit. Cheers Martin
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