[Qgis-user] point-to-point line of sight

[Bjarke Christensen]

Hi

I have point data with 1600 observations in set A and 22000 observations 
in set B, plus a DEM raster with a resolution of 1.6 meters. The data 
cover approximately 7000 square km. so the DEM is gigantic (but split up 
into 10x10 km tiles). 

I need to calculate which points in A are visible from which points in B 
(or vice versa). 

I tried running r.viewshed or r.los from the processing toolbox, to 
calculate the viewshed for just one point. With a max. distance of 2.5 km, 
that took six hours on my laptop. So running that as a batch for all 1600 
points in set A would take more than a year. 

But I am not really interested in the whole viewshed. For each point in A, 
I only want to know if it is visible from a set of perhaps 7 or 8 points 
in B that fall within a specific distance radius.

So my question is: is there any way I can calculate line of sight between 
two points or two sets of points, rather than a whole viewshed? 

Or any other way that I could speed up the calculation, so that it would 
take days or weeks rather than months or years. 

(Using QGIS 2.4 and GRASS 7 beta or QGIS 2.01 and GRASS 6.4.4)

Thanks in advance,
Bjarke Christensen.
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