[HOT] Request for information about common set of tags for HOT (Was: OSM Nepal Reponse - Links to various infos)

Carl von Einem carl at einem.net
Wed May 20 09:05:21 UTC 2015


cascafico wrote on 20.05.15 09:27:
>
> I don't know if there's a general wiki for fresh mappers; if so, it should
> point out the use of shadows casted by artifacts (stright dark lines) and
> comparison with reference elements (ie: trees).
>
> As far as I've seen, in northern Nepal most of buildings are out of tree
> canopies and we should be able to detect their shadows. Besides, a collapsed
> building often shows the rectangular shape of roof, but no shadow.

In pre desaster Bing imagery of Nepal I have seen several of those 
"shape of roof, but no shadow" but usually interpret them in a different 
way: let's assume the house has been built against a hillside, then the 
midday sun would be shining at the front of the house and the back of 
the house is "leaning" against the hill. No shadow if the roof is rather 
flat.
The same type of building built in a rather flat surrounding would 
logically produce a large shadow. Just remember the typical time of day 
when satellite imagery is shot (before noon) and if the imagery wasn't 
processed in a way so it produces "dull" light you can get a good idea 
of the topography.

Besides, I often wonder how many buildings in darker areas (such as 
close to trees or shadowed by topography) are overlooked by mappers who 
traced the same area earlier. When I look at the history of correctly 
identified objects nearby I mostly see edits done in iD. I suspect that 
iD's default setting for the brightness of background imagery is just 
too dark for most monitors.
OTOH I do a lot of panoramic photography and when stitching images I 
sometimes need to manually spot control points in overlapping image 
pairs shot with differing yaw/pitch/roll values. So I'm sort of trained 
to spot tiny details.

Cheers,
Carl



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