CelNav is a simple utility to support celestial navigation on a small boat. It provides the data listed on the daily pages of the Nautical Almanac as well as functionality for sight reduction and calculation of a fix from two LOPs taken in relatively short succession (the program will correct for motion of observer between the sights for the LOPs). It uses the PyEphem package to calculate ephemeris data for Sun, Moon, navigational planets and stars (http://rhodesmill.org/pyephem/index.html). PyEphem must be installed in order for CelNav to run (it is available for free at the URL listed above). In addition Python 2.6 or newer must be installed with Tkinter and its ttk ("Themed Tkinter") descendant.
This package is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
The archive file contains the source distribution for CelNav. It contains the following file in addition to this README:
setup.py - Python Distutils installation script. See below under "Installation".
cnscript.py - Python script with a simple main driver that will run the application. Will be installed in /opt/celnav. While you can launch the application from the command line with 'python cnscript.py' it is recommended to use the shell script 'nxcn' which performs some additional housekeeping (see below under 'data files').
PKG-INFO ⁻ Package info: some meta data about this package.
This folder contains the Python package consisting of the following modules:
celnav.py - Implements classes to calculate, store and manipulate almanac and sight reduction data. celnav.py does not contain any UI logic.
cnapp.py - Implements the application and GUI by mixing classes from celnav.py with Tkinter/ttk widget classes.
starcat.py - Contains the base data required by PyEphem for ephemeris calculations for the 57 navigational stars plus Polaris. Used instead of PyEphem's star.py which misses about 20 of the navigational stars.
cncfg.py - Uses a ConfigParser instance to read celnav.ini configuration file and to provide access to its parameter values. Imported by other modules to get access to config parameters.
classprint.py - Contains an inheritable print overload method that displays instances with their class names and a name=value pair for each attribute stored on the instance itself. Mixed into celnav and cnapp classes to aid testing.
The package will be installed into the directory that contains 3rd party distributions in your Python installation.
celnav.ini - Configuration file for setting application parameters such as path names and initial latitude and longitude values. Will be installed into $HOME/.celnav/
celnav.cfg - Xdefaults-type configuration file, defining options for the Tkinter widgtes used in the GUI. Will be installed into $HOME/.celnav. Path and filename can be changed in celnav.ini if required.
doc/ - Folder with html help files. Contents will be placed into /usr/local/share/doc/celnav. Can be accessed via the application's Help menu.
nxcn - Minimalistic shell script that executes 'python /opt/celnav/cnscript.py'. It redirects/appends stderr to $HOME/.celnav/celnav.err and puts a timestamp in that file before launching the application. It will create the directory if it doesn't exist. If the files '/etc/nx.lat' and '/etc/nx.lon' exist it is assumed that these contain most recent values for latitude and longitude in degrees (incl. decimal fractions). This is the case under Navigatrix, a common Linux distribution among cruisers (see http://navigatrix.net). If these files are found, the nxcn shell script will use lat/lon values from these files to update the INITIAL_LAT and INITIAL_LON parameters in celnav.ini prior to launching the application.
celnav.desktop - LXDE desktop file. Will be installed in /usr/local/share/applications and points to the nxcn shell script which is assumed to reside in /usr/local/bin and defines application category ("Navigation") and icon for the LXDE environment. Can be ignored if not running under LXDE.
navtriangle.png - 48x48 icon image. celnav.desktop assumes this file resides in /usr/local/share/icons/.
As mentioned above, Python 2.6 or later, Tkinter plus ttk and PyEphem must be installed for CelNav to run (the program has been tested under Python 2.6.5.). To install the celnav pacakge and its auxilliary files:
(1) Extract the contents of the archive file into any directory, preserving the folder structure.
(2) Open a terminal in the folder CelNav-0.2.0 and run
python setup.py install
at the command line. This will install the celnav package and place the
auxilliary files (e.g. icon, shell script) in their respective target
directories. Note that - depending on your system setup - you may need to
run the above command as root. In this case type
sudo python setup.py install
at the command prompt.(3) If the auxilliary files
/usr/local/bin/nxcn (shell script)
/usr/local/share/applications/celnav.desktop (LXDE desktop file)
/usr/local/share/icons/navtriangle.png (icon image file)
already exist on the target platform, these files will not be installed.
This is to avoid accidental overwriting of other files with these same
names. In this case the setup.py installation script will print a message
which of these files have been skipped during installation and ask you to
manually check whether you want to overvrite the exisiting files. In this
case you can simply copy the file(s) from the package into their respective
target directories.
Any existing files in /opt/celnav will be moved into a subdirectory
"moved_by_CelNav_0.2.0".That's it. A few notes:
Whenever a fix is calculated, CelNav will log all data for that fix to a file. The name for that file is set via the parameter LOG_FILE in celnav.ini (default: celnav.log). The file will be placed in the directory set via the variable APP_DIR in cnapp.py (default $HOME/.celnav). There is no housekeeping; the application will keep appending to the file. You can simply delete the file should it grow too big (will take a few thousand sights though...) and CelNav will start a fresh one.
CelNav can write the data contained in the "daily pages" of the Nautical Alamanc to a comma-separated text file (hourly GHA Aries, GHA and Dec for Sun, Moon and planets, plus HP for the Moon). After writing the file it will call the program defined by the parameter SPREADSHEET_PATH in celnav.ini to display the file. Default for this parameter is /usr/bin/gnumeric which shows the data in the Gnumeric spreadsheet application that is part of Navigatrix. Configure a different application executable (incl. path) in celnav.ini if you use a different spreadsheet application. You can open celnav.ini from CelNav's File menu. The program defined by SPREADSHEET_PATH will also be called to display star data and the CelNav log file (see above).
The parameter EDITOR_PATH in celnav.ini defines a text editor to be used for displaying the ini file and the error log.
The parameter BROWSER_PATH in celnav.ini defined the browser to be used for displaying the CelNav help file.
Should be straight forward. The application offers three tabs:
Allows you to enter a date and a lat/lon position and will display Sun and Moon rise/set/transit times and twighlight hours for that day. In addition it will show the Equation of Time for that day (with negative values indicating the apparent sun being ahead of the mean sun), the dates of previous and next full and new moons, and how many days the moon is into its current cycle.
All dates and times on this tab are UT. If you enter a lat/lon and press "Update Display" the times shown for the various events will be for that position but still be expressed in UT.
Pressing the "Almanac Page" button will generate a comma-separated text file with hourly GHA and Declination data for Aries, Sun, Moon and planets. CelNav will open this file in the Gnumeric spreadsheet application (or any application specified via the SPREADSHEET_PATH parameter in celnav.ini). All angles are displayed in degrees with decimal fractions (with the usual "S/W = -" sign convention) as well as in the traditional Almanac format (e.g. "N 35 17.2").
Pressing the "Star Data" button will generate a comma-separated text file with SHA and Declination data for the 57 navigational stars plus Polaris. The file will also contain altitude and azimuth data for each star for the UT and Lat/Lon entered by the user. As with the Almanac Page the file will be opened in a spreadsheet application and can be used as a simple tool to select suitable stars for a sight at a given UT.
A visual aide for quickly checking which planets are available at given UT and Lat/Lon entered by the user. The times during which planets will be above the horizon will displayed in a simple Gantt chart on a 24hr grid on which twilight periods are shaded.
This tab allows entry of the usual data for a celestial sight and will calculate intercept and azimuth for that sight. It will also calculate an intercept corrected for the motion of the observer (MOO). The latter will be used to calculate a fix from 2 LOPs as a "short run fix".
The structure of this tab has a "Fix" at its top level. Associated with the fix are vessel SOG and COG (used for the MOO correction of the intercept) and the time for which the fix is to be calculated (this allows to use a time "close to" but different from the time of sights, for example to accommodate some plotting routine or comparison with a GPS reading.
Under the Fix you can have one or more LOPs and each LOP can have one or more Sights. If there is only one LOP no Fix can be calculated but you can still reduce the Sights for that LOP. The idea of multiple Sights per LOP allows you to take a number of sights of a body in quick succession, have the application reduce all of them, and pick for example the one with the median intercept, thus eliminating any outliers (via the radio button selector to the right of the Sights).
The Fix calculation performed by CelNav is a simple 2-LOP plane geometry fix (same as you would do on a plotting sheet). The application will show an error message if you have less or more than two LOPs and press "Calculate Fix".