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

[Victor Olaya]

The Advanced Viewshed Analysis plugin has an option for calculating
intervisibility of points, and you can set a restriction of distance. Maybe
you can give it a try

To speed things up, you migh want to resample your DEM to a coarser
resolution. You might lose some detail, but i guess that in terms of
visibility you will not get a significant number of true positives or false
negatives, an it will help reducing the processing time if needed

Hope this helps




2014-07-09 15:08 GMT+02:00 Bjarke Christensen <Bjarke.Christensen at sydbank.dk
>:

> 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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