On 28/09/15 16:14, Phil Endecott wrote:
Chris Hill wrote:
I've had a go at extracting the height of buildings from the
Environment Agency LIDAR, and it seems possible.
I loaded the EA data into a database and found all the height points
within the polygon of an existing building outline. The highest value
is the height of the building.
Well it's the altitude above sea level of the roof of the building.
Presumably what OSM wants to record is the height above natural ground
level or adjacent road level or similar. I can think of various ways
of doing that, e.g. looking for the lowest point near but outside the
building outline.
No, the whole point of subtracting the DTM from the DSM data is to leave
the height above the surrounding land level. The height=* tag wants the
height of the highest point of the roof, so simply finding max() of all
of the points within the polygon of the building does that. That's the
good thing about this method.
I can also imagine looking at the distribution of heights within the
building outline and working out if it is a flat or a pitched roof.
And maybe working out which direction the ridge runs in i.e. which
wall it is parallel to.
Processing more roof detail is much harder.
I've written another blog about getting these height values:
http://chris-osm.blogspot.co.uk/2015/09/extracting-building-heights-from-lidar.html
--
Cheers, Chris
user: chillly
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