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Satellite Tracking in OpenWebGIS
openwebgis
In OpenWebGIS was added a module for visualization of satellites tracks on a map. Knowing the position of artificial satellites at each time point relative to the Earth surface is necessary for many scientific, engineering, and manufacturing problems. Similarly it may be necessary for people who want to see the satellites in the starry night sky. Satellite watching or satellite spotting is a hobby which consists of the observation and tracking of Earth artificial satellites. People with this hobby are variously called satellite watchers, trackers, spotters, observers, etc.
OpenWebGIS_Satelite1
 Figure 1.
When calculating and visualizing the satellites tracks using OpenWebGIS you can:

  1. See the track in real time,

  2. Build a track from any arbitrary point in time in the past or the future,

  3. Receive a track as a set of points or lines. When getting it in the form of points you will have the longitude, latitude, velocity, height (altitude) and time calculated for each point. When getting it in the form of lines you will have average velocity and average height (altitude) calculated for all the track,

  4. Export the track to other GIS formats - gml, geojson, csv, kml,

  5. Building the tracks, you can not just look at them, but at the same time add any other of your layers, and perform geographical and mathematical analysis of data and a variety of calculations, ie, to work like with the standard GIS because OpenWebGIS is evolving towards a fully functional GIS, moreover which is available online for everyone.


You can see the example of work with the “Satellite Tracking” module of OpenWebGIS on the video here:


In order to start working with “Satellite Tracking” module you need in the menu of OpenWebGIS select "GeoDataBase-> Satellite Tracking". Then you will see a pop-up window which is shown in the Figure 2.
OpenWebGIS_Satelite2
Figure 2.

The window has a lot of options, you will probably understand them without any difficulties, as they are named and there are tooltips that appear when a cursor is positioned over the element of interest. One of the main elements of the window is a text area where the user can insert URL of TLE-file in such format: http://wsn.spaceflight.esa.int/iss/tledata.txt or insert TLE-file in such format:
"ISS (ZARYA)
1 25544U 98067A 08264.51782528 -.00002182 00000-0 -11606-4 0 2927
2 25544 51.6416 247.4627 0006703 130.5360 325.0288 15.72125391563537 "
A two-line element set (TLE) is a data format used to convey sets of orbital elements that describe the orbits of Earth-orbiting satellites. OpenWebGIS uses the TLE to compute the position of a satellite at a particular time. By default, URL of TLE-file was inserted in the textarea to describe the motion of the International Space Station http://wsn.spaceflight.esa.int/iss/tledata.txt. This file is provided by The European Space Agency (ESA).
International_Space_Station_OpenWebGIS
Figure 3. The International Space Station on 23 May 2010 as seen from the departing Space Shuttle Atlantis during STS-132. Photo from Wikipedia.

You can get the TLE files for the number of satellites (including NOAA, GPS, Navy Navigation Satellite System (NNSS), Russian LEO Navigation and many others) from here: http://www.celestrak.com/SpaceTrack/. As well there is an archive TLE-files for 1980-2004 years.

OpenWebGIS_Satelite3
Figure 4.

After entering the TLE data you can choose 2 methods for visualizing of the satellite track.

The first method:

The satellite track can be built in real-time with the interval specified in the field "set interval of refresh in miliseconds". If this checkbox is checked "Start from date / time:" the trajectory(track) is created starting from the date you specified, otherwise the satellite track is created starting from the current UTC / GMT date / time. In this case the track is constructed as a set of points. In this case longitude, latitude, velocity, height (altitude) and time are calculated for each point. These values ​​are added to layer as its attributes. The Figure 5 shows the data of each point on the track. Note the interface changes in the main window of OpenWebGIS. The interface was changed after selecting the menu item "Interface-> Switch to interface drag" and fixed after clicking on a menu item “Interface can be dragged”. In order to opened OpenWebGIS with your interface in each starting select the menu item "Interface-> Save Interface". This ability to change the interface exists for all who do not like the default interface of OpenWebGIS. More thoroughly about it can be seen in this video:


In the future we are planning to give users even more flexibility to change the interface.

OpenWebGIS_Satelite4
Figure 5.
At the same time using standard opportunities of OpenWebGIS, you can change the layer legend with the information about the satellite track. To do this, click on the word "legend" under layer name (in this case, Satellite - but you can select any layer name), after that under the layer name will appear  the region on which you click to open the legend settings window.  Look at the Figure 6.

OpenWebGIS_Satelite5

Figure 6.

The figure 6 shows a visualization of the altitude change of the International Space Station from 411 to 432 km (green, yellow, red shows the different ranges of heights) in the interval of time 2014-11-01T02:20:35/ 2014-11-01T03:00:40.
All track parameters you can see in the table form, if you select the name of the target layer in the list of "Editable Layer" and then in the menu item "Edit-> Open attribute table". The attribute table will open in a separate window, as seen in the figure

OpenWebGIS_Satelite6
Figure 7.

The second method:

You can get the track for any period of time immediately and without per-second tracking. For this, there are buttons “Ok point layer” and “Ok line layer”. The purpose of which is clear from the title. In the first case the track is constructed as a set of points, but in the second case it is created as a set of lines. While constructing of the track in the form of lines average velocity and average height are calculated for all track. These values ​​are added to layer as its attributes. Look at the Figure 8.
The time interval for the track calculation is taken from the field "Start from date / time:" and "end date". In the figure below you can see the track built for the International Space Station after pressing  "Ok line layer" button in the time interval from 2014-11-01T02: 20: 30 to 2014-11-02T03: 00: 40. It is important: while constructing a track using the second method as a set of points ("Ok point layer") it is required more computing power and thus it is slower than when creating the track as a set of lines. The smaller the interval in the field "set interval of refresh in miliseconds:" (ie the more detailed track) the more time to calculate.

OpenWebGIS_Satelite7
Figure 8.

When drawing the track using the first method in real time you can simultaneously get tracks  for several satellites. To do this, simply insert the new TLE data in the textarea (delete the previous data), insert a new name for the layer and the satellite, press the button "Show track in real time" (in this case it is not necessary to stop the previous track), and you will get the message as shown in the Figure 9.
OpenWebGIS_Satelite8
Figure 9.

If you agree, then the new layer and the new satellite traffic information in real time are added. The Figure 10 shows the simultaneous tracking of NOAA 1 satellite and the International Space Station.

OpenWebGIS_Satelite9
Figure 10.

When you draw the track as a set of points in real-time in “Satellite Tracking” module, it is also possible to draw not all the points with accumulation but every time to leave any arbitrary number of points, such as one, two, ten, and the like, to do it, it is necessary to check the option "leave the last : ... .points”.  Look at the Figure 11.
OpenWebGIS_Satelite10
Figure 11.

It may be convenient for the users to monitor the satellite not simply as a point but as a photo or a drawing of the satellite. To do it, it is necessary to change the layer legend for the satellite track and select an image on your disk suitable as a marker by clicking button “Browse”. The Figure 12 shows this button and displays the International Space Station position in the form of a diagram taken from the site "OAO Rocket and Space Corporation Energia after SP Korolev "
OpenWebGIS_Satelite11
Figure 12.

The algorithm for calculating the satellite parameters at any particular point in time is taken from Shashwat Kandadai https://github.com/shashwatak/satellite-js.
Those who want to understand the math and physics of the process can read the calculation theory of the orbit parameters here http://www.celestrak.com/NORAD/documentation/spacetrk.pdf
Draw
Figure 13.

And
here: Orbital Coordinate Systems, Part I By Dr. T.S. Kelso
http://celestrak.com/columns/v02n01/

http://celestrak.com/columns/v02n01/
http://celestrak.com/columns/v02n03/


In the satellite track construction (in the form of a linestring) per day and more time there were problems with lines drawing. During this time, the satellite can repeatedly cross the date line. In this case, the construction of the line connecting the points that lie on both sides close to the date line appears the line that goes across the map connecting the two coordinates, as shown in the Figure 14. It is obvious that it is not correct.

OpenWebGIS_SatelError
Figure 14.

(The construction was carried out using the library of OpenLayers v. 2.12.)
The solution was found here http://gis.stackexchange.com/questions/83425/splitting-linestrings-on-the-dateline-with-openlayers/83772#83772 (by Julien-Samuel Lacroix) and implemented in the code of OpenWebGIS.