[GRASS-user] Unable to get an horizon from a DEM using r.horizon

[Mathieu Monney]

Hi all,

My goal is to extract the visible horizon given a point using a DEM I  
have successfully imported into GRASS. Using the r.horizon command it  
returns me some good result for some part of the horizon. However at  
some other angle in returns me the 0 value which means that no horizon  
has been found. I cannot understand why we cannot found a horizon.  
There always be an horizon, even if a point lies on lower altitude  
than you. I have tried to modify the r.horizon command to return  
horizon values which are also below you but it doesn't work well and  
returns me some weird results.

Anyone having some clues about that?

Thank you a lot in advance.

Best,

Mathieu Monney