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A while ago I did a neighbourhood roof orientation survey for solar panel deployment, by visually checking each roof and marking individually whether they were south or almost south-facing.

As this is very time-consuming, I would like to find a way to automate this, but don't know how this would be possible by merely analysing roof shadows.

I can script a little but have never written any plug-ins. What other elements do I need to include? We are on a very low budget, so any suggestions how to do this using open source tools would be welcome. Thanks!

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Sounds like a good machine learning exercise. –  dassouki Dec 5 '11 at 13:56
    
@globalavocado, what's the size of your study area? Also, do you have an accompanying DEM of the area? –  elrobis Dec 5 '11 at 14:20
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What kind of data do you have? Do you need to identify roofs automatically or has that been done? Can you obtain photos at two different times of day (near midday)? –  whuber Dec 5 '11 at 15:25
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@elrobis the neighbourhood area is about 500m by 1.25km. I don't have a DEM yet, but I need to do one at some point. –  globalavocado Dec 5 '11 at 16:54
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for a similar need (getting main roof orientation) I used opencarto java lib. But I work from vector data (not satelitte imagery). –  simo Dec 5 '11 at 19:05
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Is is possible that LIDAR has been flown recently in the area? You can extract buildings this way... LIDAR would most likely be too expensive to fly yourself, probably at least 8-12k for an area that size.

http://knol.google.com/k/aerial-extraction-of-roof-surfaces-for-solar-analysis#

Found that article, may be of some help.

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+1 nice article. @globalavocado, are you sure the size of your study area merits writing a program to perform the analysis? Given the size of the study area, I suspect you can get your answer faster by combing over the aerial manually. For a small area, it may take longer to write the program. Of course, if you do this frequently and with larger areas, writing a program becomes much more justified. –  elrobis Dec 5 '11 at 18:58
    
@Thad thanks for the link, hope I'll be able to follow all that! –  globalavocado Dec 5 '11 at 22:55
    
@elrobis it is a small area but I'll have to do more in the future. I would also like to expand my knowledge of how to approach this challenge. –  globalavocado Dec 5 '11 at 22:58
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I'm not sure, but it looks like youll have a hard time extracting the angle of the roof from 2-d imagery and that you need some sort of 3-d data. Post back if you get anything to work, I would be interested to know what you work out. –  Thad Dec 6 '11 at 13:09
    
Just found this as well. cybercity3d.com –  Thad Dec 6 '11 at 14:15
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