I would like to find things wrongly tagged as man_made=chimney like cooling towers or even just generic industrial buildings.

This would be very easy – because chimneys are always very slim – if I could query for man_made=chimney + give a minimum size, maybe 60 m^2.

If it's not directly possible with Overpass: I have no objections to use postgis (ogr2ogr).

Thanks in advance!

asked 15 May, 08:35

Druzhba's gravatar image

Druzhba
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accept rate: 0%


Overpass doesn't have area size filtering but you can cheat a bit and use length:

[out:json][timeout:25][bbox:{{bbox}}];
way[man_made=chimney](if:length() > 25);
out geom;

Chimneys should mostly be geometries where the relationship between area and perimeter is pretty direct, so I don't think it will catch a lot of false positives.

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answered 15 May, 12:12

maxerickson's gravatar image

maxerickson
9.4k866134
accept rate: 31%

I've mapped many chimneys in Thailand, mostly those attached to crematoria, but have never added a height because I don't have the time or equipment in the field to make such measurements. I think most chimneys are, like the ones I added, simple nodes tagged man_mde=chimney so Max's query probably won't return many objects.

Cheers,

Dave

(15 May, 16:47) AlaskaDave
1

@alaskadave - I think that this is about the ground area occupied by the feature rather than the height. There are 32k nodes, but still 7k ways, which is still a significant number.

(I'm mentioning this because I referred to this answer in reply to an entirely separate question over at the forum).

(15 May, 17:02) SomeoneElse ♦

Aha. Thanks for the clarification.

I didn't think about ground area at all so I didn't do any checking for ways vs nodes before I answered. Even knowing that, the query will produce data for only 7K out of a total of 40K objects.

(15 May, 17:21) AlaskaDave

Dave: You can "guesstimate" the height if the Bing or DG as shadows. If you have the shadow of say known height close by. eg a two story block say 6 meters by a chimney with double or triple shadow chimney will be 12 to 18 meters. I realise that Thailand might be fairley shadow free but in the UK 50 degrees north we always have shadows.

(16 May, 06:10) andy mackey
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question asked: 15 May, 08:35

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