Surya Siddhanta
दक्षिणोत्तररेखायाम् सा तत्र विषुवत्प्रभा । शङ्कुच्छायाहते त्रिज्ये विषुवत्कर्णभाजिते ॥
The Radius multiplied by the Gnomon (or 12) and the equinoctial shadow (separately) and divided by the equinoctial hypothenuse[1] gives the cosine and sine of the latitude (respectively). The arcs of these sines are the co-latitude and the latitude which are always south[2] (at the given place from whose zenith the equinoctial circle is inclined to the south).
english translation
dakSiNottararekhAyAm sA tatra viSuvatprabhA । zaGkucchAyAhate trijye viSuvatkarNabhAjite ॥
hk transliteration by Sanscript