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

Andy Robinson ajrlists at gmail.com
Thu Sep 24 18:22:14 UTC 2015


That looks really good. Very useful for tracing buildings because there is no angle distortion. You can even pick out the differences between the main block of a building outline and the lower parts such as single storey extensions and garages. One drawback is that vehicles show up but they tend to be smaller than most structures.

Be interesting to see a semi-transparent version over an aerial image to see if the two combined make tracing very easy or just confusing.

Cheers
Andy

-----Original Message-----
From: Phil Endecott [mailto:spam_from_osmgb at chezphil.org] 
Sent: 24 September 2015 18:41
To: talk-gb at openstreetmap.org
Subject: Re: [Talk-GB] Environment Agency LIDAR datasets OGL licensed now available

Chris Hill wrote:
> Suitably processed this could provide a source of building outlines.

Yes, I think it could be very useful for that.  I've had a play and rather than doing shaded relief I've just converted the height directly into a grey shade.  I've then applied ImageMagick's edge detection filter.  Here are a couple of fragments near Manchester taken from the 25cm resolution data; in each case the first image is the direct height-to-grey and the second is edge-detected:

http://chezphil.org/tmp/lidar1.png
http://chezphil.org/tmp/lidar1_ed.png
This is at SJ 8099, or maybe search for Chaseley Road to find it on a map.  You could easily trace building outlines from this and determine roof shapes and could measure building heights by subtracting roof from ground, with some suitable tool.  You could also trace trees and some walls.

http://chezphil.org/tmp/lidar2.png
http://chezphil.org/tmp/lidar2_ed.png
This is SE of the last one at SJ 8198.  The gasometers (presumably!) are at the junction of West Egerton Street and Liverpool Street.
I find it interesting that you can count the number of ridges in the large warehouse roofs.  You can also easily identify carparks!

How would people find this for tracing compared to photo imagery?


Cheers,  Phil.





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