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scripts/perl/examples/find_elevations.pl

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+#!/usr/bin/perl
+#
+# Written by Curtis L. Olson, started January 2003
+#
+# This file is in the Public Domain and comes with no warranty.
+#
+# $Id$
+# ----------------------------------------------------------------------------
+
+
+# This script will calculate the flightgear ground elevation for a
+# serious of lon/lat pairs, given one per line via stdin.  Result it
+# written to stdout.  Lon/lat must be specified in decimal degrees,
+# i.e. "-110.2324 39.872"
+#
+# This requires a copy of flightgear running with "--fdm=null" on the
+# specified "$server" host name, at the specified "$port".
+#
+# I highly recommend that you if you plan to feed a large number of
+# coordinates through this script that you presort your list by tile id #
+# That will minimize the load on the FG tile pager since you will process
+# all coordinates for a particular tile before moving on to the next.
+# Also, there is a chance the next tile will already be loaded if it is near
+# the previous (which it will tend to be if you sort by tile id.)
+
+use strict;
+
+use Time::HiRes qw( usleep );
+
+require "telnet.pl";
+
+my( $server ) = "localhost";
+my( $port ) = 5401;
+my( $timeout ) = 10;
+
+
+# open the connection to the running copy of flightgear
+my( $fgfs );
+if ( !( $fgfs = &connect($server, $port, $timeout) ) ) {
+    die "Error: can't open socket\n";
+}
+&send( $fgfs, "data" );     # switch to raw data mode
+
+
+# elevate ourselves only to make the view more interesting, this
+# doesn't affect the results
+set_prop( $fgfs, "/position/altitude-ft", "5000" );
+
+my( $last_lon ) = -1000.0;
+my( $last_lat ) = -1000.0;
+my( $last_elev ) = -1000.0;
+
+# iterate through the requested coordinates
+while ( <> ) {
+    my( $lon, $lat ) = split;
+    set_prop( $fgfs, "/position/longitude-deg", $lon );
+    set_prop( $fgfs, "/position/latitude-deg", $lat );
+
+    # wait 1 second for scenery to load
+    usleep(500000);
+
+    # then fetch ground elevation
+    my( $elev ) = get_prop( $fgfs, "/position/ground-elev-m" );
+
+    if ( $lon != $last_lon || $lat != $last_lat ) {
+        my($waitcount) = 0;
+        while ( $elev == $last_elev && $waitcount < 5 ) {
+            print "(WARNING: waiting an addition 1 second and requerying.)\n";
+            # same answer as last time, scenery is probably still loading,
+            # let's wait 1 more seconds and hope we get it right the next
+            # time, we bail after 5 seconds.
+            usleep(1000000);
+            $elev = get_prop( $fgfs, "/position/ground-elev-m" );
+            $waitcount++;
+        }
+    }
+
+    print "$lon $lat $elev\n";
+
+    $last_elev = $elev;
+    $last_lon = $lon;
+    $last_lat = $lat;
+}
+
+
+# shutdown our connection (this leaves FG running)
+&send( $fgfs, "quit");
+close $fgfs;