[Tagging] Elevation and height on vertical features

Colin Smale colin.smale at xs4all.nl
Thu Jan 7 22:56:30 UTC 2016


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.
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..


On 7 January 2016 22:50:02 CET, Warin <61sundowner at gmail.com> 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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