[GRASS-dev] d.legend: labels on smooth legends

[Ivan Shmakov]

	One more problem with d.legend is that it labels both ends of
	the scale (and places intermediate labels at equal distances.)
	However, it may be more appropriate not to label one or both
	ends.

	Consider, e. g., raster having the range -13 .. 123.  With
	d.legend placing, say, 7 labels they would be: -13, 10, 32, 55,
	78, 100, 123.  While it may be preferred to have 0, 20, 40, 60,
	80, 100, 120 labelled instead (like Gnuplot would put the tics
	on the axes by default.)

	Apparently, the current labelling algorithm is implemented with
	the following:

$ nl -ba display/d.legend/main.c 
   605		    for(k = 0; k < steps; k++) {
   606			if(!fp) {
   607			    if(!flip)
   608				tcell = min_ind + k * (double)(max_ind - min_ind)/(steps-1);
   609			    else
   610				tcell = max_ind - k * (double)(max_ind - min_ind)/(steps-1);
...
   627			}
   628			else {   /* ie FP map */
   629			    if(hide_catnum)
   630				buff[0] = 0; /* no text */
   631			    else {
   632				if(!flip)
   633				    val = dmin + k * (dmax - dmin)/(steps-1);
   634				else
   635				    val = dmax - k * (dmax - dmin)/(steps-1); 
...
   639			}
...
   689		    } /*for*/
$ 

	Any chances of making the Gnuplot-like algorithm available as an
	option?

	FWIW, here is the script I've used as a workaround to generate
	Gnuplot-like legends.  (It depends on `gnuplot', `fig2dev' and
	`convert' being in "$PATH".)

#!/bin/bash
### r.colorbox.sh --- Color boxes for GRASS rasters  -*- sh -*-

### Configuration
: ${CONVERT:=convert}
: ${D_LEGEND:=d.legend}
: ${D_MON:=d.mon}
: ${FIG2DEV:=fig2dev}
: ${GNUPLOT:=gnuplot}
: ${R_INFO:=r.info}

## FIXME: allow command line options here?
out_sfx=.eps

### Globals
name="$(basename "$0")"
verbose=yes

### Auxiliary functions

make_color_scale () {
    ## FIXME: d.mon should allow /dev/stdout as a target file
    local png="$(mktemp -t "${name}-$$.png")"
    local map="$1" out="$2"
    local prev_mon=$(${D_MON} -p \
                         | sed -e '/.*:[[:blank:]]*/!d; s///')
    GRASS_WIDTH=$[256 + 3] GRASS_HEIGHT=$[5 + 3] GRASS_TRUECOLOR=TRUE \
        GRASS_PNGFILE="$png" ${D_MON} start=PNG \
        && ${D_LEGEND} -vcs map="$map" at=0,100,0,100 \
        && ${D_MON} stop=PNG \
        || return 1
    [ -n "$prev_mon" ] && ${D_MON} select="$prev_mon"
    ## FIXME: a hack
    sleep .1s
    ${CONVERT} -crop 256x1+2+4 "$png" "$out"
    rm -f -- "$png"
}

make_gp () {
    local min="$1" max="$2"
    cat <<EOF
set terminal postscript eps
set size 1, .15
set xtics nomirror
unset ytics
unset key
set xrange [${min} : ${max}]
set yrange [2 : 3]
plot 1
EOF
}

make_fig () {
    local frame="$1"
    local grayscale="$2"
    cat <<EOF
#FIG 3.2  Produced by xfig version 3.2.5-alpha5
Portrait
Flush left
Metric
A4      
100.00
Single
-2
1200 2
2 5 0 1 0 -1 50 -1 20 0.000 0 0 -1 0 0 5
	0 ${frame}
	 225 225 5940 225 5940 812 225 812 225 225
2 5 0 1 0 -1 60 -1 -1 0.000 0 0 -1 0 0 5
	0 ${grayscale}
	 405 338 5760 338 5760 585 405 585 405 338
EOF
}

raster_min_max () {
    local raster="$1"
    ## NB: a hack
    $R_INFO -r map="$raster" \
	| sed -e 's/.*=//' \
	| sort -g \
	| tr \\n ' '
    echo
}

### Code:

if [ "$#" -lt 2 ]; then
    echo "Usage: $name PREFIX [RASTER]..." >&2
    exit 1
fi

prefix="$1"
shift

## FIXME: improve error handling
set -e

for raster in "$@"; do
    out="${prefix}${raster}${out_sfx}"
    test "$verbose" = yes \
	&& echo "* Producing ${out}..." >&2
    read min max < <(raster_min_max "$raster")
    if [ "$min" = nan -o "$max" = nan ]; then
        echo "${name}: ${raster}: Invalid data range; ignored"
        continue
    fi
    frameeps="$(mktemp -t "$name".eps-XXXXXX)"
    fig="$(mktemp -t "$name".fig-XXXXXX)"
    color_scale="$(mktemp -t "$name".ppm-XXXXXX)"
    make_color_scale "$raster" \
        "ppm:${color_scale}"
    make_gp "$min" "$max" \
	| $GNUPLOT > "$frameeps"
    make_fig "$frameeps" "$color_scale" \
	| $FIG2DEV -L eps \
	> "$out"
    rm -f -- "$color_scale" "$frameeps" "$fig"
done

### r.colorbox.sh ends here

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