Aerospace applications of Perl

Aerospace Applications of Perl

Presented by Ian KluftSilicon Valley Perl

Santa Clara, CaliforniaMarch 3, 2016

Aerospace Applications of Perl

● Perl and its libraries on CPAN are versatile● Aerospace applications cover lots of topics

– Navigation/mapping

– Aviation

– Satellites

– Astronomy

● Also some examples from my own projects

Introducing the presenter

● Hi! I'm Ian Kluft● From San Jose and a native

of the Bay Area● Software engineer

– Primarily Perl & C/C++ on servers & embedded/IoT

– Perl is my favorite language

● Currently working on my MBA

● Aerospace enthusiast– Commerical pilot & flight

instructor– Co-founder of Stratofox

Aerospace Tracking Team

– Participated in world records for amateur aerospace

● 1st amateur rocket launch to space (CSXT 2004, Nevada)

● 1st transcontinental/transoceanic Ham Radio balloon (CNSP 2011)

Navigation & Mapping

● I presented a year ago at SVPerl on Geographic Computation● Quick overview here because positioning is integral to

aerospace– Next 7 slides are a review from last year's presentation

● Then we'll move on to look at aviation, satellites & astronomy

Coordinate systemLatitude and longitude

● Any position on Earth has a coordinate● 3-dimensional positioning uses 3 numbers

– Latitude (north/south)

– Longitude (east/west)

– Altitude (relative to mean sea level/MSL)

● Latitude & longitude are specified in degrees● Altitude is specified in distance

Latitude and longitudeWhat kind of degrees?

● Not from a university● Not related to temperature● They are angles!● More precisely, angles from the

center of the Earth● Latitude = 0-90° up or down● Longitude = 0-180° either way

around

7

Earth is not a perfect sphere

● Earth is an ellipsoid: bulges out at equator– Centrifugal force from rotation causes this

● Geoid: mathematical models for Earth ellipsoid– Good models come from satellite measurement

● Coordinates must use the same geographic reference system– Otherwise comparing apples and oranges

– WGS84 most widely used coordinate system today

● Sea level and altitude are relative to this model

8

Lots of angles in Geospatial Data

● Many computations involve angles– Latitude and longitude are angles

● Manipulations use trigonometric functions● Trig functions use radians

– So numbers in degrees must be converted to and from radians

– One circle = 360 degrees = 2 * pi radians

– Radians derive 2 * pi from distance around circle relative to radius

● Math::Trig module on CPAN can do this for you

9

Great Circle Routes

● Great Circle: direct route over Earth's surface– Along a line that goes around

the sphere

– i.e. from San Jose to London crosses Greenland

– Flat-projection maps distort great circle routes to look like curves

Map generated by the Great Circle Mapper copyright © Karl L. Swartz. http://www.gcmap.com/

http://www.gcmap.com/

http://www.kls2.com/%7Ekarl/

http://www.gcmap.com/

10

Great Circle Formulas

● See “Aviation Formulary” sitehttp://williams.best.vwh.net/avform.htm

● Distance between points● Course between points● Latitude of point on GC● Lat/lon given radial & dist● Intersection of 2 radials● Max latitude of a GC

● GC crossing a parallel● Intermediate points on a GC● Cross track error● Along track distance● Point known offset from GC

Many of these are in Math::Trig

http://williams.best.vwh.net/avform.htm

11

Example: Great CircleDistance between points

● From scratch:

d=acos(sin(lat1)*sin(lat2)+cos(lat1)*cos(lat2)*cos(lon1-lon2))

● In Perl:

use Math::Trig 'great_circle_distance';

$distance = great_circle_distance($lon1, $lat1, $lon2, $lat2, $radius);

● Convert angles to radians● For the radius of the Earth, use 6366.71 km

– Don't forget to convert result from km to miles if needed

12

Navigation related Perl modules

● Net::GPSD3 – connect to GPSD v3 server so multiple processes can use a single GPS on laptop, IoT, drone, etc

● Geo::Coder – use online search sites to look up address of current location

● Geo::Cache – Look up geocaching sites nearby● Ham::APRS::IS – receive Ham Radio APRS positioning data,

open-sourced by the APRS.FI Ham Radio tracking web site● Many more

13

Aviation applications

● Adding to the navigation/planning capabilities…● Geo::METAR – decode text from airport weather observations● Geo::TAF – decode text from airport weather forecasts● Geo::ICAO – encode/decode international airport codes● And other variants of these

14

Aviation example:METAR weather observation (1/5)

#!/usr/bin/perl

use strict;

use warnings;

use Getopt::Long;

use LWP::UserAgent;

use HTTP::Response;

use XML::Simple;

my $url = "http://www.aviationweather.noaa.gov/adds/dataserver_current/httpparam?dataSource=metars&requestType=retrieve&format=xml&stationString=%s&hoursBeforeNow=4";

my @metar_fields = qw(observation_time temp_c dewpoint_c wind_dir_degrees

wind_speed_kt wind_gust_kt visibility_statute_mi altim_in_hg

sea_level_pressure_mb three_hr_pressure_tendency_mb wx_string

sky_condition vert_vis_ft maxT_c minT_c maxT24hr_c minT24hr_c precip_in

pcp3hr_in pcp6hr_in pcp24hr_in snow_in quality_control_flags

flight_category

);

my $ua = LWP::UserAgent->new();

15

Aviation example: METAR weather observation (2/5)

# convert temperature C to C & F

sub tempC2CF

{

my ( $tempc ) = @_;

my $tempf = int($tempc * 9 / 5 + 32 + .5); # .5 = round off

return sprintf "%dC/%dF", $tempc, $tempf;

}

# turn a sky condition structure into a string

sub sky2str

{

my ( $sky ) = @_;

if ( ref $sky eq "ARRAY" ) {

# handle arrays of cloud layers by recursive calls

my @result;

foreach my $layer ( @$sky ) {

push @result, sky2str( $layer );

}

return join " ", @result;

}

# report cloud layer

return $sky->{sky_cover}."@".$sky->{cloud_base_ft_agl};

}

16


# get_metar function - download METAR by airport code

sub get_metar

{

my ( $code ) = @_;

my $url_with_code = sprintf( $url, $code );

print $url_with_code."\n";

my $response = $ua->get( $url_with_code );

if ( $response->is_error()) {

printf "%s failed: %s\n", $code, $response->status_line;

} else {

my $content = $response->content();

my $metar_tree = XMLin( $content );

print "$code:\n";

if ((!exists $metar_tree→{data})or (!exists $metar_tree→})

or (!exists $metar_tree->{data}{METAR})) {

print "unrecognized data: $content\n";

} else {

my $metar_ref = $metar_tree->{data}{METAR};

foreach my $metar ( @$metar_ref ) {

foreach my $field ( @metar_fields ) {

if ( exists $metar->{$field}) {

if ( $field eq "observation_time" ) {

print $metar->{$field}." ";

} elsif ( $field eq "sky_condition" ) {

print "sky: ".sky2str($metar->{$field})." ";

} elsif ( $field =~ /^(.*)_c$/ ) {

my $name = $1;

print "$name:".tempC2CF($metar->{$field})." ";

} elsif ( $field =~ /^(.*)_(kt|statute_mi|in_hg|degrees)$/ ) {

my $name = $1; my $unit = $2;

print "$name:".$metar->{$field}."$unit ";

} else {

print "$field:".$metar->{$field}." ";

}

}

}

print "\n";

}

}

}

}

17


# main - get airport codes from command line, loop through them and get METARs

my $arg;

foreach $arg ( @ARGV ) {

get_metar( $arg );

}

18


● Example usage: get_metar KRHV

krhv:

2016-03-04T01:51:00Z temp:19C/66F dewpoint:14C/57F wind_dir:320degrees wind_speed:4kt visibility:10.0statute_mi altim:30.050198in_hg sky: OVC@5000 flight_category:VFR

2016-03-04T00:51:00Z temp:19C/66F dewpoint:14C/57F wind_dir:0degrees wind_speed:4kt visibility:10.0statute_mi altim:30.050198in_hg sky: OVC@3500 flight_category:VFR

2016-03-03T23:53:00Z temp:21C/70F dewpoint:13C/55F wind_dir:320degrees wind_speed:11kt visibility:10.0statute_mi altim:30.041338in_hg sky: BKN@4000 OVC@6000 flight_category:VFR

2016-03-03T22:53:00Z temp:22C/72F dewpoint:13C/55F wind_dir:0degrees wind_speed:4kt visibility:10.0statute_mi altim:30.059055in_hg sky: BKN@4000 OVC@6000 flight_category:VFR

19

Satellite tracking

● Why would you want to track a satellite?– See visible passes of International Space Station (or Iridium Flares),

nighttime only– Ham Radio communication via OSCARs (Orbiting Satellite Carrying

Amateur Radio), day or night– If you make a commercial or research satellite, you'll build your own

ground station, day or night

● Astro::SpaceTrack – downloads satellite orbital elements● Astro::satpass – makes satellite pass predictions● Astro::App::SatPass2 – makes satellite pass predictions

20

Astronomy

● Astro::Sunrise – compute sunrise/sunset for your location/date● Astro::MoonPhase – compute phase of the moon for a date● Astro::Telescope – for astronomers accessing remote

telescopes● Various celestial database searches

21

Example: Missing rocket payloadat Black Rock Desert

Location: Black Rock Desert, Nevada

Problem: Rocket launched, payload missing● Soka University (Japan) students needed data● Payload was a “CanSat”, size of a soda can● AeroPac club knew rocket landing coordinates● Turned to Stratofox Aerospace Tracking Team● Transmitter batteries died before they contacted us● I wrote a Perl script to generate a grid search

22

Perl Script to Plot Search Grid

● Search area was 3x3 mile parallelogram– Top/bottom side east-west for typical non-storm wind direction

– Right/left sides NNE/SSW for typical storm wind direction

● Each side divided into 10 sections, 1584' long● 10x10 loop projects each computed waypoint● Command-line controls output to text or GPX● “gpsbabel” open source utility turns GPX into many formats

– Raw Garmin waypoint data for upload to GPS

– KML for display on Google Earth

23

Projecting Search Grid Waypoints

● Nested loop: i = 0-10 over, j = 0-10 up● Over = 270° heading, up = 330° heading● Convert lat/lon from degrees to radians● Use Great Circle projection formula

– Compute intermediate point from i “over”

– Compute final point from j “up”

● Convert new lat/lon from radians to degrees● Code available at slideshare.com with slides

24

Sample codeconvert feet to radians

● Convert distance in feet to radians over Earth's surface● Radians are angles – this is a tiny angle from center of Earth# conversion: distance in feet to radians

sub dist_ft2rad

{

my $ft = shift;

my $km = $ft / 3280.8399; # ft/km

return $km/6371.0; # divide by FAI standard Earth radius in km

}

25

Sample codecompute waypoint from course & distance

sub gc_waypoint

{

my $lat1 = shift; # latitude (radians)

my $lon1 = shift; # longitude (radians)

my $tc = shift; # true course (radians)

my $d = shift; # distance (radians)

my $lat = asin(sin($lat1)*cos($d)+cos($lat1)*sin($d)*cos($tc));

my $dlon = atan2(sin($tc)*sin($d)*cos($lat1),cos($d)-sin($lat1)*sin($lat));

my $lon=fmod($lon1-$dlon+pi,2*pi) - pi;

return ( $lat, $lon ); # lat/lon in radians

}

26

Example codecompute coordinates of search grid point

# project a waypoint in the search area

# shape of a parallelogram with sides at headings 030 (NNE) and 090 (east)

# sides are on heading 1 (030 degrees) and heading 2 (090 degrees)

# increments are 0-10

# each increment is 1584 ft so that 10 of them is 3 miles

sub project_waypoint

{

my $h1_inc = shift;

my $h2_inc = shift;

# compute intermediate point on the first side of parallelogram

my ( $lat_r1, $lon_r1 ) = gc_waypoint (

deg2rad( $point_start[0]), deg2rad( $point_start[1]),

$h1_heading, $rad_per_increment * $h1_inc );

27

Example code (continued)compute coordinates of search grid point

# compute final projected waypoint in search area

my ( $lat_r2, $lon_r2 ) = gc_waypoint (

$lat_r1, $lon_r1,

$h2_heading, $rad_per_increment * $h2_inc );

# convert radians to degrees

my $lat = rad2deg( $lat_r2 );

my $lon = rad2deg( $lon_r2 );

return ( $lat, $lon );

}

28

Search Area Grid Map

Result of the script shown on Google Earth

29

Result: Success!!!

Expected to be worse than needle in a haystack

Payload found 2500' west of rocket landing site

30

Conclusions

● The sky is not the limit● You can have fun and learn a lot solving problems like these

Q & A

Engineering

Aerospace applications of Perl