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<p>So if all the elevations in OSM should be interpreted as WGS84, but many (most?) of them are not, we have no way of knowing which are "right" and which are "wrong". Even if the numerical value of ele=* is correct, we have unreliable data.</p>
<p>Where do we go from here? Maybe we should encourage an explicit reference to the datum used, such as ele:wgs84=* or ele:osgb=*? Or should we heuristically assume that no mappers will have translated elevations to wgs84 anyway, and change the wiki to make the definition into "national standards"?</p>
<p>According to wikipedia [1] the differences between the datums can be up to 100m.</p>
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<p>--colin</p>
<p>[1] https://en.wikipedia.org/wiki/Sea_level#Height_above_mean_sea_level</p>
<p>On 2016-01-08 12:00, Martin Koppenhoefer wrote:</p>
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<div class="gmail_quote">2016-01-08 2:30 GMT+01:00 Warin <span><<a href="mailto:61sundowner@gmail.com">61sundowner@gmail.com</a>></span>:<br />
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<div>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. </div>
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<div>don't confuse elevation and height. Elevation is typically referring to the ground. For a mountain, the situation is clearly different, it is the peak we are mapping, not the mountain, because it is not even clear what a mountain is (where it starts).<br /><br /></div>
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<blockquote type="cite" style="padding: 0 0.4em; border-left: #1010ff 2px solid; margin: 0">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..</blockquote>
Good point there! <span><span> :-) </span></span><br /> For most it won't matter. What do international planes use as there reference for height? Use that - again consistency.</div>
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<div>why planes? If you fly a plane you have to have specific airspace maps, nothing where OSM is particularily useful. Normally, maps are using elevation indications in the national system. AFAIK, we have already standardized elevation indications: they're * in WGS84 like all our data. </div>
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<div class="gmail_extra">Cheers,</div>
<div class="gmail_extra">Martin<br /><br /></div>
<div class="gmail_extra">* well, they should be, typically the mappers read the elevation off some sign and don't bother to convert. <br /><br /></div>
<div class="gmail_extra">PPS: Sorry, it isn't actually clear that WGS84 should be used, I have just discovered that the "meters above sea level" indication has already been introduced in 2008 in the post-vote-cleanup phase ;-)<br /><a href="http://wiki.openstreetmap.org/w/index.php?title=Key%3Aele&type=revision&diff=151029&oldid=125595">http://wiki.openstreetmap.org/w/index.php?title=Key%3Aele&type=revision&diff=151029&oldid=125595</a></div>
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