[GRASSLIST:4926] Re: 100KM raduis viewshed
jidanni at dman.ddts.net
Mon Nov 11 03:39:25 EST 2002
>>>>> "G" == Glynn Clements <glynn.clements at virgin.net> writes:
>> I want to concentrate on just 30 degrees of my horizon. That means
>> I must use mapcalc to make a patt_map mask that any cell with the
>> azimuths I want to be =1. A pie slice shaped mask. Hmmm. How to
G> Probably the simplest method would be to create a vector map
G> consisting of a single polygon, then convert it to a raster map with
I wouldn't know where to begin there. Alternatively?
G> Alternatively, you could compute the heading relative to the centre
G> of the map (or any other point) using the (undocumented)
G> two-argument form of r.mapcalc's atan() function, e.g.
G> r.mapcalc "eval(heading = atan(x() - $xc, y() - $yc), ...
G> Note: the argument order is the reverse of ANSI C's atan2() function.
$ xc=235577 yc=2675353 ;\
r.mapcalc "eval(heading = atan(x() - $xc, y() - $yc), \
nantou.triang = heading>140 && heading<170)"
you have confused me
I even tried if(heading...)
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