How do we draw building outlines for water towers? Often they have a small base and a larger top, and only in few cases both are visible in the aerial imagery.

In this case (OSM) both are visible. Should I only draw the base instead of as of now, the top? The drawn top moved to the "real" location, that is of the base, would also cover the footpath beside it, as I guess is done in many situations. Right now, the top is drawn at where the top is located on the imagery, which is of course in the wrong location...

asked 09 May '13, 22:59

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Grillo
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edited 09 May '13, 23:05


Imagine that you are viewing the building exactly from above and draw the outline based on that. In practice, this is usually achieved by tracing the "roof" (the top of the tower in your case) and dragging it over the base.

You should not move the footway from its actual location - if it is below the tower's top in reality, then it will and should be overlapped by the tower's building outline.

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answered 10 May '13, 00:35

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Tordanik
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Ok, that's what I thought... I only wanted to check if the base or the top was the mapping "target", since they usually differ the most with water towers. The only problem now is that the way that's "below" the water tower will give validator/keepright errors, but I guess those should be ignored.

(10 May '13, 04:22) Grillo

Hmm, I'd do the opposite and map what was at ground level, not the crow's view.

(10 May '13, 08:43) SK53 ♦

@SK53: I can see reasons for both, and as is often the case with OSM, it's unlikely that one mapping style is strictly followed everywhere. What I described was the convention that the 3D community preferred when we discussed this problem in the context of Simple 3D Buildings. The advantages of mapping the crow's view are pretty clear e.g. for buildings on stilts imo.

It should be noted that, by using building:part areas, you could describe the situation more precisely. They aren't used by Mapnik or the validator, though.

(10 May '13, 13:22) Tordanik

I would draw around the top and drag it over the base. As I am sure you know we have to estimate the position when drawing building viewed off vertical. I would also put the path as close as possible to the tower not through it. see http://wiki.openstreetmap.org/wiki/Roof_modelling

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answered 09 May '13, 23:37

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andy mackey
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edited 09 May '13, 23:44

Uhm, but moving the footway makes no sense? Or is this the preferred way of doing this anyway?

(09 May '13, 23:39) Grillo

Your other comment " will give validator/keepright errors " was my sense, If it were a road would it become a bridge?

(10 May '13, 07:39) andy mackey
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question asked: 09 May '13, 22:59

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last updated: 10 May '13, 13:22

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