[GRASS-user] query values within different angles

[Tim Besser]

Thank you Hamish,

worked pretty good for my purposes. But as I am a beginner in GRASS I 
need to ask what the $ sign stands for. Because when I applied your 
solution with the $-sign and just copied it the resulting maps were 
rather coarse in resolution. So I tried and left the $ sign away. The 
result was a map in the same resolution as the original map.

Thanks for quick help!

Cheers Tim

Am 31.05.2011 12:33, schrieb Hamish:
> Tim wrote:
>> I need to query raster values around a city for different
>> angles. The result I am aiming at should be the amount of
>> landcover surrounding the city within 10 degrees angles and
>> different distances to the city.
>>
>> So far I tried r.buffer and v.buffer but that are not
>> providing what I am lookin for. Using r.mapcalc and
>> addressing each pixel separately would be an option but I
>> hope that GRASS combined with perhaps PGSQL and Postgis
>> functions provides an easier way to achieve that.
>>
>> I would highly appreciate any hints how to derive buffers
>> for specific angles only.
> Hi,
>
> in years past I had a version of r.los for GRASS 5.0 where instead
> of reporting the vertical angle to the source point I had it
> report horizontal compass heading. I'm sure it's on an old hard
> drive somewhere, but in hindsight using r.mapcalc and some simple
> trig would be a heck of a lot easier and more efficient than
> anything else. No other tools are needed beyond that one amazing
> module.
>
>
> #spearfish
> g.region -d
> g.region -c
>    center easting:  599490.000000
>    center northing: 4920855.000000
>
> Ce=599490
> Cn=4920855
>
> r.mapcalc "angle_to_pt.cartesian = atan(x() - $Ce, y() - $Cn)"
> r.mapcalc "angle_to_pt.compass.1 = 90 - angle_to_pt.cartesian"
> r.mapcalc "angle_to_pt.compass = if(angle_to_pt.compass.1<  0, \
>     angle_to_pt.compass.1 + 360, angle_to_pt.compass.1)"
> g.remove angle_to_pt.compass.1
>
>
> MIN_ANGLE=0
> MAX_ANGLE=10
>
> r.mapcalc "MASK = if(angle_to_pt.compass>= $MIN_ANGLE \
>     &&  angle_to_pt.compass<  $MAX_ANGLE, 1, null() )"
>
> d.redraw
>
>
>
>
> Hamish
>
>