Find features (e.g. man_made=chimney) exceeding a certain size limit

Question

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!

Accepted Answer

2

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 '18, 12:12

maxerickson
12.7k●10●83●176
accept rate: 32%

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 '18, 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 '18, 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 '18, 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 '18, 06:10) andy mackey

Find features (e.g. man_made=chimney) exceeding a certain size limit

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