Hi Will, On Wed, Jul 9, 2008 at 8:11 PM, Will <[EMAIL PROTECTED]> wrote: > On Wed, Jul 9, 2008 at 12:11 PM, Paul Kelly <[EMAIL PROTECTED]> wrote: >> On Wed, 9 Jul 2008, Will wrote: ... > I am having a great time doing this work; I am funded from an NSF grant > that Laura has. Hopefully I'll be able to get funding from Google next > summer and contine working with GRASS.
this is great and much appreciated! ... >> Observer elevation is a useful shortcut to have and especially relevant >> for radio masts etc. Do you have a default observer elevation in r.viewshed? > > Observer elevation will not be too hard to implement, so I can put it in. > As of right now, the default observer elevation for r.viewshed is ground > level. For r.los, the default value is 1.75- does anyone on the list have > an opinion on if I should make 1.75 the default for r.viewshed, or if it > should be a different value? Since it is rather arbitrary, please keep it for backward compatibility. >> Earth curvature calculation would seem to be important when covering a >> very large area, but I imagine it is not the simplest thing to add so it may >> not be necessary immediately. I must confess I have no idea how much of a >> difference it makes to the calculation, nor what is the threshold when it >> starts to become an important consideration. Perhaps someone else on the >> list can comment. > > Looking at the r.los code, it doesn't seem to be too hard to put in > curvature, though like you I have no idea what effect it has or at what > threshold it becomes important. It is important - please, if not too hard (I ported it from r.cva to r.los, wasn't so hard) add it. It makes a difference... I have an ongoing "batlle" with an ex colleague if we can see the sea from our mountain here or not, r.los and his algorithm do not agree. :) > It is done exactly the way you mentioned in the other email, finding the > radius of the elipsoid and reducing the elevatin of the cell that you are > looking at depending on the distance it is away from the viewpoint. The way > r.los does it is they have a flag that you set if you want the curvature to > be considered, though I can impliment it for all calculations without a flag > if we think that will be better- any input from the list on this? I would keep the flag if there aren't too many. Benjamin provided a useful link in his mail. Markus _______________________________________________ grass-dev mailing list grass-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-dev
