A detailed description of how EQMOD gets the equatorial coordinates
A detailed description of how EQMOD gets the equatorial coordinates

Author: Mon

1. Read the RA and DEC Stepper ring counter values from the stepper board

  • Values are 32BIT Hexadecimal Ring counter values
  • Ring counter center value is 0x800000
  • A single increment (decrement) of the counter corresponds to 0.144 arcsecond of mount movement on each axis

2. Get the PC Local Time and the site's Latitude, Longitude, Elevation

  • data provided by the user or the GPS module and is fed to the EQMOD driver
  • data stored in the windows registry

3. Compute for the Local Sidereal Time/date based on the PC Local Time, Site Coordinate data, and the RA ring counter value

4. Get the Hour Angle based on the LST and date and other factors such as obliquity and nutation.

5. Get the DECLINATION equatorial coordinate based on DEC motor ring counter value

6. Compute for RIGHT ASCENSION equatorial coordinate based on the Local Sidereal Time and Hour angle, RA coordinate and PIER status

  • Notice that the Right Ascension is also dependent on the DEC motor. The Right Ascension values change when the DEC motor moves to the other side of the pier.

7. Publish the values on the display and on the upper application layers such as the Planetarium application

8. Repeat from Step 1

As you can see, the values are still based on the RA and Dec motor ring counter values (Step 1). Even if the EQMOD driver is shutdown and restarted and as long as the power is not removed from the mount, you will be able to continue the operation without starting from the home position.

/home/welshdra/public_html/eqmod/data/pages/a_detailed_description_of_how_eqmod_gets_the_equatorial_coordinates.txt · Last modified: 2008/11/06 15:03 (external edit)
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