[PROJ] Converting WGS 84 to Gauß-Krüger

[Dominik Vogt]

I have a shell script that converts Gauß-Krüger coordinates (which
are still used by some Germand botanists) to WGS 84.  It looks
roughly like this:

	# RW and HW contain the "Rechtswert" and "Hochwert" in GK (Potsdam
	# datum)
	# Figure out the source coordinate system, depending on the first digit
	# of the "Rechtswert", i. e. the "Meridianstreifen":
	case "$RW" in
		(2*) CS="epsg:31466"  ;;
		(3*) CS="epsg:31467"  ;;
		(4*) CS="epsg:31468"  ;;
		(5*) CS="epsg:31469"  ;;
		(**) CS="epsg:31467"  ;;
	esac
	# convert to WGS 84
	echo "$RW" "$HW" |
		cs2cs +init="$CS" +to +init=epsg:4326 |
		read LON LAT JUNK

Now I need to do the reverse transformation.  There is no obvious
way to guess the right destination coordinate system.  Is there a
simpler way than just trying all four and see which one yields the
correct result?

	for CS in epsg:31466 epsg:31467 epsg:31468 epsg:31469; do
		echo "$LAT" "$LON" |
			cs2cs +init=epsg:4326 +to +init="$CS" |
			read RW HW JUNK
		# if RW and HW are good, return them, otherwise try next CS
	done

Ciao

Dominik ^_^  ^_^

-- 

Dominik Vogt