[GRASS-user] r.horizon and negative tilt

[Mark Lake]

Frank,

Some years ago I wrote a module (also called r.horizon) which I 
think does what you want.  I never got around to formally 
contributing it (must compare with the existing r.horizon and do 
so some time).  Anyhow, have updated for GRASS 7 and will send you 
the code direct - it compiles as r.horizon2 to avoid collision 
with the existing module.

Regards,

Mark

Frank David <frank.david at geophom.fr> writes:

> Ho yes, why not. I could use r.viewshed to find the farest part 
> of the
> topography able to see my point and get it's angle mode. The 
> trick to
> find is how to get that cell ?
> Best regards,
> frank
>
> Le 30/07/2018 à 11:18, balotti.and at gmail.com a écrit:
>> Il 30/07/2018 09:24, Frank David ha scritto:
>>> Hi Andrea,
>>> Thanks for your message. But what is the ground plane ? 
>>> r.horizon use
>>> the topography, so nothing is plane (and the earth curvature 
>>> tends to
>>> lower the ground).
>> Yes, what you explain below is what I mean with "ground plane".
>>> I guess as the calculation is done at ground level, the 
>>> minimum
>>> viewable horizon cannot be lower than zero. The calculation 
>>> should be
>>> done higher than ground level to "see" negatives horizon.
>> Have you taken a look to r.viewshed? I never tried it but maybe 
>> is
>> useful for your purposes.
>>> Never mind I will try to create my own r.horizon with 
>>> r.transect or
>>> r.profile.
>>> Best regards,
>>> Frank
>> Best regards,
>> Andrea
>>
>>> Le 30/07/2018 à 08:47, balotti.and at gmail.com a écrit:
>>>> Hi Frank,
>>>> just my opinion but r.horizon I suppose is targeted to solar
>>>> radiation modules and because of that returns only the 
>>>> line-of-sight
>>>> "obstacles" above the ground plane, where direct sunlight may 
>>>> be
>>>> obstructed by obstacles.
>>>> best regards,
>>>>
>>>> Andrea Balotti
>>>>
>>>> Il 28/07/2018 15:59, Frank David ha scritto:
>>>>> Dear all,
>>>>>
>>>>> It seems that r.horizon in does not return negative 
>>>>> heights. How
>>>>> it's possible in case of the given point from the 
>>>>> calculation is
>>>>> done is located on mountain and the horizon around is below 
>>>>> zero
>>>>> ??. I miss something may be...
>>>>>
>>>>> Thank you for your explanations
>>>>>
>>>>> Regards
>>>>>
>>>>> Frank
>>
>>
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--
Dr Mark Lake
Senior Lecturer in Archaeology

UCL Institute of Archaeology
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