[Tagging] Elevation and height on vertical features

Greg Troxel gdt at ir.bbn.com
Fri Jan 8 19:19:06 UTC 2016


Martin Koppenhoefer <dieterdreist at gmail.com> writes:

> the advantage for the mapper is that it is quite easy, you simply read
> an elevation off a sign and add the reference height system to the
> value. (yes, you have to know what is this reference height system,
> that's why the "quite" is there). I'd also prefer to have uniform

indeed. I see height signs on mountains and it's hard for me to figure
out if it is NGVD29 or NAVD88.

> values in the same system, but if the alternative to having a value in
> a local system is not having any value at all, I'd prefer the values
> in other datums (and marked as such).

Certainly editors could be set up to accept inputs in other datums and
convert.  I just don't think it makes sense to store it that way.  There
are far fewer editors than programs using the db, so that would be less
work.   And if we store height in other datums, why not horizontal?

> FWIW, for most usages of these ele values it doesn't really matter if
> a value is 20 meters more or less, they are used to get a rough idea,
> not to be used in calculations where a meter more or less is
> important, i.e. this discussion is mostly theoretical...

Agreed.
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