On 8/01/2016 9:56 AM, Colin Smale wrote:
Nobody will be using the raw data to fly a plane. It doesn't matter if
we use the ele tag for the top or the bottom - as long as the height
is given, the other value can easily be derived. What is important is
consistency, both in its definition and it's usage. Defining it as
sometimes the top and sometimes the bottom of a feature doesn't help.
And consistent with other mapping products/practices?
By convention maps uses blue to indicate sea, rivers and streams.
The idea is to be readily usable by using the same practice as others
have used in the past.
Not to set some new standard where there is no reason for it.
Grasping at straws .. the elevation of a mountain is given as its peak.
If there is consistency within the map then the elevation of all objects
should be their maximum height.
We will also need to standardize on a datum for elevations. The wiki
refers to both mean sea level (which varies by country) and wgs84. The
differences might be enough to take the wheels off your plane..
Good point there! :-)
For most it won't matter. What do international planes use as there
reference for height? Use that - again consistency.
By maintaining some consistency with what has been done elsewhere it
will make it easier to compare, check and confirm OSM data.
On 7 January 2016 22:50:02 CET, Warin <[email protected]> wrote:
On 8/01/2016 3:32 AM, Christoph Hormann wrote:
On Thursday 07 January 2016, Aaron Spaulding wrote:
Hi all, I’ve been working on generating 3D meshes based on
OSM data and I ran into a problem. Vertical features like
'natural=cliff', 'barrier=retaining_wall’ and
'waterway=waterfall' occupy two points in physical space,
but because of the 2D nature of OSM its ambiguous which
side of the feature that the ‘ele’ tag applies.
For cliffs mapping conventions say that you should put the
line on top of the cliff in case it is not exactly vertical -
accordingly the ele tag would also refer to the top - but keep
in mind that the elevation does not have to be constant.
Consider who is going to use the map, and for what purpose.
The most critical use is for aeroplanes .. where the maximum height is
critical information!
I think for that reason alone most maps should indicate the maximum
elevation of an object.
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