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I am looking for the best way to run a visibility analysis in PostGis 2, i.e. given 2 points and obstacle polygons, are these 2 points visible from each other ?

I did not find anything relevant for now. Are you aware of :

  • such a function
  • a library I could use to perform this
  • or do I have to implement it by myself ?

Thanks in advance

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Not one which im aware, but SAGA has one , GRASS has one, QGIs has one in SEXTANTE toolbox. Probably easiest way would be use grass or saga from commandline to calculate it. Also i think all mentioned programs have open source –  simplexio Mar 20 '13 at 11:33
    
Is this a 2D analysis? –  Scro Mar 20 '13 at 12:20
    
Yes this is a 2d analysis –  FredB Mar 20 '13 at 12:31
    
Why do you want to do it in PostGIS and not in a "real" GIS? If you were using (as mentioned) grass or QGIS, it would be very easy. –  til_b Mar 20 '13 at 13:37
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1 Answer

up vote 2 down vote accepted

You can do this with SQL. Without knowing how you're getting your data, I'd guess something like:

SELECT ST_Intersects([the polygon geom], ST_LineFromWKB([point A geom], [point B geom])) AS Is_Obscured

Obviously this is not a complete query. If it's not enough to point you in the right direction, then you'll need to share some more details.

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It seems there is ST_3DIntersects. using that requires 3d data... But after reading that 2D comment i assume that Z dosent affect visibility –  simplexio Mar 20 '13 at 12:59
    
I made the same assumption. Another assumption here is that the distances are short enough to ignore the whole geometry vs. geography great circle issue. –  Scro Mar 20 '13 at 13:08
    
But then you can cast (or transform) geometry to geography (i think) –  simplexio Mar 20 '13 at 13:15
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