There are four major methods of calculation in Astronomy
They are
Longitudes calculated along the Zodiac or Ecliptic – The Ecliptic System
Longitudes calculated along the Celestial Equator – The Equatorial System
Longitudes calculated along the Celestial Horizon – The Horizontal System
Longitudes calculated along the Celestial Meridian – The Meridian System
Longitude measured along the Kranti Vritta, the Ecliptic or Bha Chakra , the Zodiac is known as Kranti Vritteeya Sphuta, the true longitude of the planet.
Longitudes measured along the Vishuvat Vritta, the Celestial Equator is known as Vishuvat Vritteeya Sphuta, Right Ascension.
Udaya Lagna, the Ascendent and Astha Lagna, the Descendent are measured along the Celestial Horizon,The Kshitija
And the Madhya Lagna, the MC and the Patala Lagna, the IC are measured along the Celestial Meridian, the Nadi Vritta.