#!/bin/bash

RES="$1"
IN="$2"
SCALED="${IN%.tif}_${RES}px.tif"
OUT="${SCALED%.tif}.txt"

# resize tiff image to desired resolution
convert "$IN" -resize $RES "$SCALED"

# convert to txt file
convert "$SCALED" "$OUT"

# replace ": (" with ","
sed -i 's/: (/\,/' "$OUT"

# remove all unneeded entries at end of line
sed -i 's/).*$//' "$OUT"

# convert longitude and latitude to the right values
# 0..RES => -180..180
# 0..RES/2  => -90..89
mv "$OUT" "$OUT.tmp"
awk -F, '{$1=$1*360/'$RES'-180;$2=-1*($2*360/'$RES'-90);}1' OFS=, "$OUT.tmp" > "$OUT"
rm "$OUT.tmp"

# remove unneeded header
sed -i '1d' "$OUT"

# add blank lines for pm3d
sed -i "${RES}~${RES}G" "$OUT"

# add new header
sed -i '1s/^/# long, lat, r, g, b\n/' "$OUT"