[Talk-GB] Environment Agency LIDAR datasets OGL licensed now available

[Chris Hill]

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