[GRASS-user] How to find out an angle between to points on the map (for r.plane, r.lake) - shellscript

[Dylan Beaudette]

On Saturday 01 March 2008, Philipp Steigenberger wrote:
> Dylan Beaudette schrieb:
> > On Thursday 28 February 2008, Philipp Steigenberger wrote:
> >> Hi
> >> I want to work with r.plane and r.lake to get simulate floodings in
> >> DTMs.
> >>
> >> In the section of interest there is a river which runs from about SSW to
> >> NNE. For r.plane I need the
> >> azimuth. Is there a tool in GRASS which tells me the angle between two
> >> points I mark on the map like I can measure in between two points with
> >> d.measure?
> >
> > Simple trigonometry is a start. Or on a computer the atan2() function is
> > useful:
> >
> > atan2( (end_y - start_y) , (end_x - start_x) ) * 180/pi
>
> Dylan Beaudette schrieb:
> > attached is a patch (against todays SVN) to optionally print the bearing
> > between clicks.
> >
> > Dylan
>
> Dylan,
> sorry, I have no idea how to incllude this patch to my system.
> I'm neither good in R or C or Fortran or Python.
>
>  > attached is a patch (against todays SVN
>
> (Also I have problems to install the actual SVN)
>
> But I'm used to write shell scrpits, so I wrote this one for bc.
>
> #!/bin/sh
> LIST_1=`d.what.rast -t1`
> E1=`echo $LIST_1 | awk -F : '{print $1}'`
> N1=`echo $LIST_1 | awk -F : '{print $2}'`
>
> LIST_2=`d.what.rast -t1 --q`
> E2=`echo $LIST_2 | awk -F : '{print $1}'`
> N2=`echo $LIST_2 | awk -F : '{print $2}'`
>
> SCALE="scale=8"
> pi=$(echo "scale=10; 4 * a ( 1 )" | bc -l)
>
> echo "epsilon = `echo "$SCALE;  360-( a ( ( $E1 - $E2 ) / ( $N1 - $N2 )
> ) ) * 180 / $pi" | bc -l`°"
> echo "if epsilon > 360"
> echo "epsilon' = `echo "$SCALE;  ( a ( ( $E1 - $E2 ) / ( $N1 - $N2 ) ) )
> * 180 / $pi * -1" | bc -l`°"
>
> In GRASS I work in Transversal Mercator (Gauß-Krüger)
> I know the script isn't perfect, cause it doesn't work if N1 = N2, but
> for me this doesn't matter.
>
> Philipp

Philipp,

Glad to hear that you were able to make something which worked for you. I have 
submitted the patch to d.measure to the tracker, and may be integrated into 
GRASS proper if it is deemed useful by the dev crowd.

Cheers,

Dylan


-- 
Dylan Beaudette
Soil Resource Laboratory
http://casoilresource.lawr.ucdavis.edu/
University of California at Davis
530.754.7341