Date (DD.MM.YYYY):

      To provide GLONASS visibility zone calculation for the definite date (daily interval) user should enter into the corresponding fields the geographic coordinates of the Earth’s surface point (latitude, longitude), minimal elevation angle as well as the date in DD.MM.YYYY format as of that he needs to calculate visibility zones.
Latitude, longitude and elevation are given in degrees with decimal chare, e.g. 37.5.
     Longitude ranges from 0º to 90º, also North or South latitude should be specified in appropriate field;
     Latitude ranges from 0º to 180º, also East or West longitude should be specified in appropriate field;
     Elevation ranges from 0º to 90º (elevation 5 º is recommended for open territory and 25 º in urban area);
     The calculation date is set in DD.MM.YYYY format (e.g. 31.12.2008) recommended range is no more than one month from the current date(to provide calculation accuracy).
After filling the form, user must click on the "Calculate visibility zone" button.
     The graphic representation of the GLONASS visibility zones as of the specified date, will be given in the browser window in 20-30 sec. The time scale conforms to the discrete (winter) Moscow time, numbers of SC GLONASS corresponds to their orbital slots in the constellation.
In the case of entering incorrect information by the user, as well as failures during the calculation or server’s operation, an error message will be displayed in the browser window. The current GLONASS system almanac, received by the IAC equipment, is used as the source data (besides the information, entered by the user).
      During the calculation, the information from both usable and unusable, at the current moment SC, is taken from the almanac (on the diagram they are colored in red and black, respectively).
The integration is performed using the twelfth order Adams method, which uses the following model: gravity field 4×4, the Sun’s and the Moon’s gravity fields’ calculation is based on "Yearbook" information. Methodological error of calculation on the daily time period is less then 1 sec.