Configuring from a satpass initialization file

Since the intent is to remove the satpass compatibility when satpass is retired, you may at some time wish to convert your satpass initialization file to a "Astro::App::Satpass2" initialization file. To do this from inside the satpass2 script, simply issue the command

 satpass2> save -changes

The name and location of the saved file depend on your operating system, but will be reported when you issue this command. Once the file is saved, you can display its location using

 satpass2> initfile

The configuration file's location is actually determined using "File::HomeDir->my_dist_config( 'Astro-App-Satpass2' )". See the File::HomeDir documentation for details.

Subsequent runs of the satpass2 script will initialize from the new file. This form of the "save" command just saves changes from the default configuration. If you wish to save all configuration, omit the "-changes" option.

Be aware that "save" only saves the configuration of the "Astro::App::Satpass2" object and its related helper objects. If your initialization file does other things, like download data and make predictions, these will not be written to the new file, and you must add them back by hand.

Configuring manually

Specifically, you need your latitude, longitude (from Greenwich England), and height above sea level. The height is least critical, and any reasonable guess will probably work.

Latitude and longitude can be specified in either decimal degrees (e.g. 40.5) or degrees, minutes and seconds (e.g. 40d30m0s). South latitude and West longitude are negative.

Height is assumed to be in meters, but you can be specify it in feet by appending 'ft'. For example, '10' specifies 10 meters, as does '10m', but '10ft' specifies 10 feet.

Because it would be painful to specify your position every time you use it, "Astro::App::Satpass2" allows a configuration file. The example that follows will end by creating a configuration file and storing the configuration in it.

And here, finally, is the example. We make the egregious assumption that the President of the United States uses this software, so we use the executive mansion as our location.

 $ satpass2
 ... front matter displayed ...
 satpass2>
 satpass2> # This is a comment, as is any line beginning
 satpass2> # with a hash mark ('#'). Comments and blank
 satpass2> # lines are ignored.
 satpass2>
 satpass2> # Enter the name of our location. This is for
 satpass2> # information only, and will be displayed by
 satpass2> # the location command. Command arguments that
 satpass2> # contain spaces need to be quoted.
 satpass2> set location '1600 Pennsylvania Ave, Washington DC'
 satpass2>
 satpass2> # Set our latitude and longitude.
 satpass2> set latitude 38d53m55.5s longitude -77d2m15.7s
 satpass2>
 satpass2> # Set our height above sea level.
 satpass2> set height 54.72ft
 satpass2>
 satpass2> # Some of our data sources will try to fetch
 satpass2> # their data from Space Track when we ask for
 satpass2> # it. We are assuming no Space Track username,
 satpass2> # so we tell them to just give us what they have.
 satpass2> spacetrack set direct 1
 satpass2>
 satpass2> # Some data sources come either with or without the
 satpass2> # actual name of the spacecraft. We want the name
 satpass2> # if it is available.
 satpass2> spacetrack set with_name 1
 satpass2>
 satpass2> # Save our configuration. All we really need to
 satpass2> # save are the changes from the default.
 satpass2> save -changes
 satpass2>
 satpass2> # We can now exit. When we restart, we will get
 satpass2> # the configuration we just set up.
 satpass2> exit

Geocoding the address

This requires two more optional modules: Geo::Coder::OSM and Geo::WebService::Elevation::USGS. With these installed, the address entry in the previous example becomes

 satpass2> geocode '1600 Pennsylvania Ave NW, Washington DC USA'

When you issue this command, the geocoded location is displayed, formatted as "set" commands:

 set location '1600 Pennsylvania Avenue Northwest,
   Washington, District of Columbia USA'
 set latitude 38.8976989
 set longitude -77.036553192281
 set height 18.81

If more than one result is returned, all are displayed but no location is set. If no result is returned, an exception is raised.

Visible Passes

* The satellite must be above the horizon (of course!),

* The Sun must be shining on the satellite (they do not have lights), and

* The Sun must not be shining where you are (otherwise the sky is too bright to see the satellite).

The example is for the International Space Station, and we will use NASA's predictions of its orbit over the next week as a starting point.

 $ satpass
 ... front matter ...
 satpass2>
 satpass2> # Tell the Astro::SpaceTrack object to fetch us
 satpass2> # all the predicted orbital elements from NASA's
 satpass2> # Human Space Flight web site. We include the
 satpass2> # effective date, since the data may include
 satpass2> # planned changes in orbit.
 satpass2> spacetrack spaceflight -all -effective
 satpass2>
 satpass2> # Make the default pass prediction, which is for
 satpass2> # seven days starting today at noon.
 satpass2> pass

You may want to print this information and stick it on your refrigerator. "Astro::App::Satpass2" has something a bit like Unix output redirection to get your information into a file:

 satpass2> pass >pass.txt

After which you open pass.txt in some simple editor and print it. A word-processing editor will probably not work satisfactorily unless you set the entire document to a mono-space font.

You may want a prediction for some specific date. The following example does a prediction for the night of April 1 2011 (specifically, for one day starting at noon on that day) and saves the output in april_fool.txt.

 satpass2> pass '2011/4/1 12:00:00' +1 >april_fool.txt

Note that the date is quoted because of the space between the date and the time. If you had Date::Manip installed, you could specify the date more flexibly, as (say) '1-Apr-2011 noon'.

Different Viewing Conditions

The settings discussed below are part of your configuration, and can be saved using

 satpass2> save -changes

as discussed above. If you have already saved your configuration you will be asked whether you want to overwrite the old configuration. Any answer beginning with 'y' (case-insensitive) will be considered true. Any other answer will be considered false.

The horizon

"Astro::App::Satpass2" assumes that you do not have a very good horizon, and that you can not see a satellite until it is at least 20 degrees above the horizon, and therefore does not report passes that do not get at least 20 degrees above the horizon. If you are at the beach you may be able to see to within 5 degrees of the horizon. You can configure "Astro::App::Satpass2" to report passes more than 5 degrees above the horizon by

 satpass2> set horizon 5

If you are on the top of a mountain, you may even be able to see a bit over the normal horizon. If you can see 2 degrees over the horizon,

 satpass2> set horizon -2

Twilight

"Astro::App::Satpass2" does not predict visible passes that occur during the day, and it defines day as any time after the start of morning twilight and before the end of evening twilight. These in turn are defined as the point when the upper limb of the Sun passes above or below a given distance below the horizon.

By default, "Astro::App::Satpass2" uses civil twilight to decide whether it is day or night. This is defined as the point at which the upper limb of the Sun is 6 degrees below the horizon. For a dimmer satellite, you may want to use nautical twilight (9 degrees below the horizon) or astronomical twilight (12 degrees below the horizon). You can change to nautical twilight using

 satpass2> set twilight nautical

and similarly for astronomical. Or, you can define your own twilight by entering it in degrees, remembering that degrees below the horizon are negative. If you are looking for the International Space Station, you may be able to spot it with the Sun only 3 degrees below the horizon:

 satpass2> set twilight -3

All Passes

 satpass2> set visible 0

which turns off the latter two checks and reports any pass of the satellite over your location, visible or not. To go back to predicting just visible passes,

 satpass2> set visible 1

Predicting Flares

 $ satpass2
 ... front matter ...
 satpass2>
 satpass2> # Download the data on Iridium satellites.
 satpass2> spacetrack celestrak iridium
 satpass2>
 satpass2> # Predict flares for the next seven days,
 satpass2> # starting today at noon.
 satpass2> flare

This will take a while, because it has to cover all 66 in-service Iridium satellites, 24 hours per day. And this does not include spares, which are usually kept under control, just to prove that they work. If you want them as well,

 satpass2> flare -spare

If you want a copy of all this to stick on your refrigerator door, capture it to a file in the same way you captured the pass data:

 satpass2> flare >flare.txt

If you want to append it to the pass.txt file created for satellite passes,

 satpass2> flare >>pass.txt

just as you would under Unix.

But maybe you are not interested in daylight flares. If not,

 satpass2> flare -noday

If you are also not interested in flares at 4:00 AM,

 satpass2> flare -noam -noday

or equivalently,

 satpass2> flare -pm

The "-am", "-day", and "-pm" options select which flares are reported, by time. The "-am" option selects flares from midnight until the start of morning twilight; "-day" selects flares from the start of morning twilight to the end of evening twilight, and "-pm" selects flares from the end of evening twilight until midnight.

The options can be negated by prefixing "no" to the option name (e.g. "-noday"). If you specify no options, they are all considered to be asserted. If you specify no asserted options, all unspecified options are considered to be asserted. Otherwise, only explicitly-asserted options are considered to be asserted.

If you do not want flares for a particular part of the day, calculations for that part of the day are not done. This can speed the prediction process.

Different Flare Visibility

Obviously a flare that would be fairly bright at night might be completely invisible during the day, so day and night have separate settings to control the minimum reportable brightness. "Astro::App::Satpass2" uses the "flare_mag_day" setting to determine the dimmest reportable flare during the day; this defaults to "-6". The dimmest reportable flare at night is determined by the "flare_mag_night" setting, which defaults to 0.

In order to duplicate (fairly closely) the Iridium flares reported by <https://www.heavens-above.com/>, you will want to tweak "Astro::App::Satpass2"'s settings a bit:

 satpass2> set twilight -1.8 flare_mag_night -1

seems to come fairly close.

Location

 satpass2> location

command. The output of this can be directed to a file, just as the output of any other command. For a nice list of passes and flares for your refrigerator door, you can do something like this:

 satpass2> location >this_week.txt
 satpass2> spacetrack spaceflight -all -effective
 satpass2> pass >>this_week.txt
 satpass2> spacetrack celestrak iridium
 satpass2> flare -pm >>this_week.txt
 satpass2> exit

Date and Time Format

The date and time format settings belong to the formatter object, which is a separate subsystem all to itself. So:

 satpass2>
 satpass2> # Display the date as weekday day-month-year
 satpass2> formatter date_format '%a %d-%b-%Y'
 satpass2>
 satpass2> # Display the time as 1-12 AM or PM
 satpass2> formatter time_format '%I:%M:%S %p'
 satpass2>
 satpass2> # Save the configuration, overwriting any previous one
 satpass2> save -changes -overwrite

The Julian Calendar

If you install DateTime::Calendar::Christian and properly configure "satpass2", you will be able to both parse and display dates in both the Gregorian and Julian calendars.

Parsing Julian Calendar Dates

The primary date parser is Date::Manip, which does not support Julian dates. But if you use the "ISO8601" parser, you can configure it to parse a date as either Julian or Gregorian, depending on the date itself.

What you have to do, in general, is use date parser Astro::App::Satpass2::ParseTime::ISO8601, and set its back_end attribute to 'DateTime::Calendar::Christian'. You must, of course have this module installed, and you can shorten the setting to just 'Christian'. You should see the documentation for full details, but with the "satpass2" script the configuration would look something like this:

 satpass2> # Configure the ISO8601 parser, with back end
 satpass2> set time_parser ISO8601,back_end=Christian

The DateTime::Calendar::Christian module takes, as one of the arguments to "new()", a reform date, which defaults to the date it was first adopted in Italy, on October 15 1582 (Gregorian). If you want something different you can append it to the value of "back_end" and quote the whole value. The quotes must be either escaped or surrounded with outer quotes to protect them from the command parser. For example, to set the UK reform date, use

 satpass2> set time_parser "ISO8601,back_end='Christian,reform_date=uk'"

Formatting Julian Calendar Dates

Here, you need to use the "DateTime" date formatter, which will be the default if the DateTime module is installed. Since DateTime is a prerequisite for DateTime::Calendar::Christian, installing this will make the proper date formatter the default. But before you can actually get Julian output dates, you need to configure the time formatter to use this class. Because the date formatter is managed by the formatter object, the "satpass2" commands to configure it are

 satpass2> # Configure the time formatter and reform date
 satpass2> formatter time_formatter \
 > DateTime::Strftime,back_end=Christian

A non-default reform date is specified the same way as for the parser, and the two reform dates need not be the same.

The "DateTime" "strftime" formatter also supports, as a special case, format pattern '%{calendar_name}', which renders as either 'Julian' or 'Gregorian' as appropriate. Given

 satpass2> formatter time_format \
 > '%{year_with_era}-%m-%d %{calendar_name}'

The date of the assassination of Julius Caesar would be displayed as

 '44BC-03-15 Julian'

In point of fact, the way the "%{calendar_name}" machinery works is that if the back end provides the "is_julian()" method, you get 'Julian' if that method returns a true value, and 'Gregorian' if it does not. If the back end does not provide the "is_julian()" method, whatever follows 'DateTime::Calendar::' in the back end's class name is used. If the back end does not begin with 'DateTime::Calendar::', 'Gregorian' is used.

Formatting Julian calendar dates in Astro::App::Satpass2::FormatTime::DateTime::Cldr is unsupported, because DateTime::Calendar::Christian lacks the "format_cldr()" method. You may find that it works, because this module patches in "format_cldr()" when it loads DateTime::Calendar::Christian if it finds that that method does not already exist. But you may find that it does not work, because the patch messes with the internals of DateTime::Calendar::Christian, and those might change without warning. Caveat coder.

Time Zones

Without any optional modules, the only supported zone other than your default local zone is GMT. You can get GMT output by

 satpass2> formatter gmt 1

The default ISO-8601-ish time parser does not have a corresponding setting, but does allow you to append a 'Z' to the time to specify GMT.

The default formatter object also has a "tz" setting, but this is unsupported because it relies on the "TZ" environment variable, and the author has no control over whether your OS' POSIX code supports this. You can try it with something like

 satpass2> formatter tz MST7MDT

(for Mountain time). If it works, fine. If not, you can make it work by installing DateTime and DateTime::TimeZone. Doing this also gives you the Olson database zone names (e.g. "America/New_York") if you prefer these.

Similarly, if you install the optional Date::Manip module, you can set a default input zone other than your own by something like

 satpass2> time_parser tz MST7MDT

The "time_parser" and "formatter" time zones are set separately not only so that you can make them different, but because the author can not guarantee that the underlying modules will accept the same settings.

Command Macros

The definition of a macro is simply the list of commands it issues. Each command is a single argument, and therefore probably needs to be quoted. When the command to be issued itself contains quotes, you either use a different style (single versus double quotes) or you escape the quote mark with a back slash ('\'). A simple macro definition would be something like

 satpass2> macro defined hi 'echo "Hello world!"'

When a command macro is executed it can be passed arguments. The details of how these work will be deferred for the sake of getting on with the tutorial, but a case of interest is the fact that "$@" (the quotes being part of the syntax) expands to all the arguments passed to the macro.

Multiple Locations

The first thing our hypothetical user needs is a command macro to set the location to his or her home location. The definition comes from our first example:

 satpass2> macro define home \
 > "set location '1600 Pennsylvania Ave, Washington DC'" \
 > "set latitude 38d53m55.5s longitude -77d2m15.7s" \
 > "set height 54.72ft"
 satpass2>

Normally, this would all have to go on the same line, but "Astro::App::Satpass2" recognizes an end-of-line back slash as a continuation mark, so all four lines above are parsed as though they are the same line. "Astro::App::Satpass2" changes the prompt for a continuation line, just to keep you on your toes.

Now we need another place to visit -- say, the residence of the Prime Minister of Canada:

 satpass2> macro define sussex_drive \
 > "set location '24 Sussex Drive, Ottawa, ON'" \
 > "set latitude 45.444348 longitude -75.693934" \
 > "set height 50m"
 satpass2>

Now, to switch locations to the Prime Minister's residence, just say

 satpass2> sussex_drive
 satpass2>
 satpass2> # and to confirm it,
 satpass2> location
 Location: 24 Sussex Drive, Ottawa, ON
           Latitude 45.4443, longitude -75.6939, height 50 m
 satpass2>

And to return home, just say

 satpass2> home

Of course, these are really only useful if they are in your initialization file. And they can be, with the usual incantation:

 satpass2> save -changes -overwrite

Temporary Settings

 satpass2> macro define iridium_flare \
 > 'localize twilight flare_mag_night' \
 > 'set twilight -1.8 flare_mag_night -1' \
 > 'flare "$@"'
 satpass2>

Note the use of single quotes rather than double quotes to enclose the "flare" command. In double quotes, or outside quotes altogether, the "$" is magical, and introduces something to be interpolated into the command. Exactly what is interpolated depends on what follows the "$". The $@ is replaced by the arguments of the command macro (or whatever), but we do not want this to happen until the command macro is expanded. Enclosing the $@ in double quotes ensures that macro arguments containing spaces remain single arguments; without the double quotes they would become multiple arguments.

So if you say

 satpass2> iridium_flare -noam 'today 12:00' +3

The "twilight" and "flare_mag_night" settings will be changed, the flare prediction will be run, and the old "twilight" and "flare_mag_night" settings will be restored. Because the macro arguments get passed to the "flare" command, the prediction will be for the three days starting at noon today, and will exclude flares occurring between midnight and the beginning of morning twilight.

Note that only attributes of the "Astro::App::Satpass2" object (those set with a "set" command) can be localized; attributes of helper objects can not be. But you can localize the entire helper object. For example, for a temporary change to the Astro::SpaceTrack object,

 satpass2> localize spacetrack

inside the appropriate scope. Yes, you can localize outside a command macro (or any other localization scope, such as inside a "source" file or a "begin"-"end" block), but it does no good to do so, because the old value is not restored until you exit, and what good is that?

Reporting Position

Deciding what to display is the job of the "formatter" helper object. Normally this is an Astro::App::Satpass2::Format::Template, and for the full story you should see the documentation to that class.

But there are a number of prepackaged coordinate sets:

 az_rng --------- azimuth (with bearing) and range
 azel ----------- elevation and azimuth (with bearing)
 azel_rng ------- elevation, azimuth (with bearing) and range
 equatorial ----- right ascension and declination
 equatorial_rng - right ascension, declination and range

By default, you get "azel_rng", but you can get any of the others via the local_coord() method of the formatter object. For example, if you want right ascension, declination and range, just

 satpass2> formatter local_coord equatorial_rng

User-defined Position Coordinates

 satpass2> formatter template azel <<'EOD'
 > [% data.azimuth( bearing = 2 ) %]
 >     [%= data.elevation %]
 > EOD

See the Astro::App::Satpass2::FormatValue documentation for what format effectors are available. Inside the template, the "data" object will contain the data you want to format.

Code Macros

Code macros are currently unsupported, though it might be better to call them experimental. The real situation is that I have been looking for ways to plug bits of code into the system, and handling them like macros seemed to be the best way. So I knocked something together along those lines, and played with it. Further experience may show that the interface or the implementation was ill-chosen, or even that there is something deeply flawed about the whole idea. The bottom line is that if you want this to become supported, you should tell me what you like or do not like about it.

In order to implement code macros, a number of previously-private methods of Astro::App::Satpass2 have been exposed. The names of these begin with a double underscore ("__"), and these are documented as unsupported. These will not go away even if code macros do, but their calling sequences may change. On the other hand, if code macros become fully supported, these will too.

A code macro is simply a Perl subroutine which is called by "Astro::App::Satpass2" more or less as though it were an interactive method. In the following discussion, some words are used with particular meanings:

must

means that the code macro will not work unless this is done;

should

means that the code macro will work without doing this, but you might not like the results;

may

means that the code macro will work without doing this, but you might want the functionality described.

Now, Perl subroutines do not live in a vacuum. They in fact live in Perl modules; that is, .pm files defining a "package" whose name reflects the path name of the file. A module that defines a code macro can be installed like a normal Perl module, but can also live in the lib/ directory in the user's "Astro::App::Satpass2" configuration directory (which is the default for "$satpass2->macro( load => ... )"), or anywhere if you specify the location via the "lib" option (e.g. "$satpass2->macro( load => { lib => something }, ...").

In addition to the things that go into making a Perl module, a module that provides code macros:

must be a subclass of "Astro::App::Satpass2";

must import "__arguments()" from "Astro::App::Satpass2::Utils".

In order to work as a code macro, a subroutine:

must have the "Verb()" attribute

Subroutine attributes are declared after the name (and signature if any) and a colon.

The contents of the parentheses that follow the attribute name will be split on white space and used as Getopt::Long option specifications should these be needed to process the subroutine's arguments.

may have the "Configure()" attribute

If this attribute is present, the contents of the parentheses will be used to configure the Getopt::Long object prior to processing the subroutine's arguments.

must call "__arguments()" to unpack @_

This subroutine is imported from Astro::App::Satpass2::Utils. See this documentation for details of its use.

should report warnings and exceptions properly

In order to have warnings and exceptions be handled consistently with the rest of "Astro::App::Satpass2", "$self->whinge()" should be called instead of "warn" or "Carp::carp()", "$self->wail()" should be called instead of "die" or "Carp::croak() ">, and "$self->weep()" instead of "Carp::confess() ">.

must return human-readable results

This almost goes without saying, since it is the string returned by the subroutine which will be displayed.

The arguments passed to your code macro will be, in order, the invoking "Astro::App::Satpass2" object, a reference to the hash generated by parsing the arguments, and the non-option arguments, in order.

Your package may define a code macro named "after_load()". If this is defined, it will be called as soon as the package has been successfully loaded. The arguments will be those of the "macro load" itself.

You should be aware that the first argument to your code macro subroutine is the "Astro::App::Satpass2" object that called it. This is not reblessed into the package that contains the code macro, so it is not an invocant in the usual sense. This has several implications, including:

• You can not call other code in your module as methods;

  This is a direct result of the "invocant" not being blessed into the name space of your module.

• Your code macro can not be called as a method;

  This is because nothing has been done to make it appear in the invocant's name space.

• Your code can not recurse, even indirectly via a command macro.

  This is because all macros become undefined within the scope of their own execution, so that a macro of any sort that redefines an interactive method has access to the original method.

If you want to call your code macro from inside Perl code, you must call it as

 $satpass2->dispatch( your_code_macro => ... );

and capture any output that is returned. Note that you can still specify options either command-line style or as a hash reference in the second argument to "dispatch()".

You should be cautious about calling "dispatch()" inside your code macro, except perhaps as "return $self->dispatch( ... )". If you call it internally, you probably need to be sure you concatenate the output of your calls, and return that.

A number of methods of Astro::App::Satpass2 may be useful in your code macro, and in fact were exposed for the use of code macros. These include:

__choose()

This can be used to obtain bodies from the observing list or the sky, optionally filtered. See especially the "bodies" and "sky" options.

__format_data()

This can be used to pass the raw data generated by your code macro to a "Template-Toolkit" template. It returns the resultant text.

__parse_angle()

This can be used to parse angle arguments. The return is (usually) the angle in degrees.

__parse_distance()

This can be used to parse distance arguments. The return is the distance in kilometers.

__parse_time()

This can be used to parse time arguments. The return is a Perl time.