[GRASS5] Re: d.polar using d.graph

[Markus Neteler]

Hamish,

On Fri, Mar 17, 2006 at 02:21:29AM +1300, Hamish wrote:
> Markus wrote:
> > The d.polar is waiting for a volunteer to change the xgraph
> > dependency to GRASS' d.graph. Maybe done in a few minutes for someone
> > who knows the syntax of d.graph input... The xgraph input
> > is just a title and coordinate pairs to draw the polar
> > diagram.
> 
> 
> well, here's a proof of concept; messy, but it does plot something--
> 
> `cat` and $FOO in d.graph's stdin is the required magic..
> 
> I've done it after-the-fact, but factoring x,y to 0-100% could be done 
> right in the "sin()*r, cos()*r" step to save time & space.

I wouldn't mind if someone improves the script.
 
> notes:
> my 1000x1000 aspect grid made 50mb temp files!
> 
> I got weird output when trying from r.slope.aspect (elev from 
> r.surf.contour). Spikes every 45degree. I thought I had my awk
> wrong.. [d.histogram of it attached]. Probably an artifact of blocky
> r.surf.contour output? That histogram is interesting.. smaller peaks
> 22.5deg out of phase with the 45deg spikes..? odd.

Check if you produced an integer DEM. If so, then it is no
surprise (see comments in r.slope.aspect manual).
 
> Is 0deg north-up or does it have to be rotated?  angle_n_up = 90-theta

0deg is East as common notion in GRASS (except for r.param.scale).
But north is up in the diagram (I think).

> The script could use lots of optimization.. move $2*$3/$4 stuff into one 
> coefficient before running awk, etc., e.g.
>   echo "\"All Data incl. NULL"           > ${TMP}_outercircle
>   RADIUS_COEFF=`echo "$TOTALNUMBER $TOTALVALIDNUMBER $MAXRADIUS" | \
>      awk '{printf "%.8f", $1/$2 * $3}'`
>   for i in `seq 0 360` ; do
>     echo "$i $RADIUS_COEFF" | awk ...

You are kindly invited to take a look.


> The following doesn't honour the undef= option, is it on purpose?
>  # unit vector on raw data converted to radians without no data:
>  cat ${TMP}_raw | grep -v '^*'| awk 'BEGIN {sum = 0.0}

No, fixed. 


> d.polar code follows (insert at end of script before cleanup)
> ---------------------

...

This looks promising. 
Maybe some power user picks it up and also adds the ring and
the directional indicator.

thanks for the proof of concept,

Markus